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Lightweight Access Point Protocol
draft-ohara-capwap-lwapp-04

Versions:
This document is an Internet-Draft (I-D) that has been submitted to the Independent Submission stream. This I-D is not endorsed by the IETF and has no formal standing in the IETF standards process.
The information below is for an old version of the document that is already published as an RFC.
Document	Type	This is an older version of an Internet-Draft that was ultimately published as RFC 5412.
Authors	Michael Williams , Nancy Cam-Winget , Scott G. Kelly , Rohit Suri , Susan Hares , Bob O'Hara , Pat R. Calhoun
Last updated	2018年12月20日 (Latest revision 2007年03月02日)
RFC stream	Independent Submission
Intended RFC status	Informational
Formats	txt htmlized bibtex bibxml
Stream	ISE state	(None)
Consensus boilerplate	Unknown
Document shepherd	(None)
IESG	IESG state	Became RFC 5412 (Historic)
Action Holders	(None)
Telechat date	(None)
Responsible AD	Dan Romascanu
Send notices to	capwap-chairs@ietf.org, rfc-editor@rfc-editor.org
Email authors IPR 2 References Referenced by Nits Search email archive
draft-ohara-capwap-lwapp-04
Control and Provisioning of P. Calhoun
Wireless Access Points Working B. O'Hara
Group R. Suri
Internet-Draft N. Cam Winget
Intended status: Informational Cisco Systems, Inc.
Expires: September 3, 2007 S. Kelly
 Facetime Communications
 M. Williams
 Nokia, Inc.
 S. Hares
 Nexthop Technologies, Inc.
 March 2, 2007
 Light Weight Access Point Protocol
 draft-ohara-capwap-lwapp-04.txt
Status of this Memo
 By submitting this Internet-Draft, each author represents that any
 applicable patent or other IPR claims of which he or she is aware
 have been or will be disclosed, and any of which he or she becomes
 aware will be disclosed, in accordance with Section 6 of BCP 79.
 Internet-Drafts are working documents of the Internet Engineering
 Task Force (IETF), its areas, and its working groups. Note that
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 http://www.ietf.org/shadow.html.
 This Internet-Draft will expire on September 3, 2007.
Copyright Notice
 Copyright (C) The IETF Trust (2007).
Calhoun, et al. Expires September 3, 2007 [Page 1]
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Abstract
 In the recent years, there has been a shift in wireless LAN product
 architectures from autonomous access points to centralized control of
 light weight access points. The general goal has been to move most
 of the traditional wireless functionality such as access control
 (user authentication and authorization), mobility and radio
 management out of the access point into a centralized controller.
 The IETF's CAPWAP WG has identified that a standards based protocol
 is necessary between a wireless Access Controller and Wireless
 Termination Points (the latter are also commonly referred to as Light
 Weight Access Points). This specification defines the Light Weight
 Access Point Protocol (LWAPP), which addresses the CAPWAP's protocol
 requirements. Although the LWAPP protocol is designed to be flexible
 enough to be used for a variety of wireless technologies, this
 specific document describes the base protocol, and an extension that
 allows it to be used with the IEEE's 802.11 wireless LAN protocol.
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Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 8
 1.1. Conventions used in this document . . . . . . . . . . . 9
 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10
 2.1. Wireless Binding Definition . . . . . . . . . . . . . . 11
 2.2. LWAPP State Machine Definition . . . . . . . . . . . . . 12
 3. LWAPP Transport Layers . . . . . . . . . . . . . . . . . . . 21
 3.1. LWAPP Transport Header . . . . . . . . . . . . . . . . . 21
 3.1.1. VER Field . . . . . . . . . . . . . . . . . . . . . 21
 3.1.2. RID Field . . . . . . . . . . . . . . . . . . . . . 21
 3.1.3. C Bit . . . . . . . . . . . . . . . . . . . . . . . 21
 3.1.4. F Bit . . . . . . . . . . . . . . . . . . . . . . . 21
 3.1.5. L Bit . . . . . . . . . . . . . . . . . . . . . . . 22
 3.1.6. Fragment ID . . . . . . . . . . . . . . . . . . . . 22
 3.1.7. Length . . . . . . . . . . . . . . . . . . . . . . . 22
 3.1.8. Status and WLANS . . . . . . . . . . . . . . . . . . 22
 3.1.9. Payload . . . . . . . . . . . . . . . . . . . . . . 22
 3.2. Using IEEE 802.3 MAC as LWAPP transport . . . . . . . . 22
 3.2.1. Framing . . . . . . . . . . . . . . . . . . . . . . 23
 3.2.2. AC Discovery . . . . . . . . . . . . . . . . . . . . 23
 3.2.3. LWAPP Message Header format over IEEE 802.3 MAC
 transport . . . . . . . . . . . . . . . . . . . . . 23
 3.2.4. Fragmentation/Reassembly . . . . . . . . . . . . . . 23
 3.2.5. Multiplexing . . . . . . . . . . . . . . . . . . . . 24
 3.3. Using IP/UDP as LWAPP transport . . . . . . . . . . . . 24
 3.3.1. Framing . . . . . . . . . . . . . . . . . . . . . . 24
 3.3.2. AC Discovery . . . . . . . . . . . . . . . . . . . . 24
 3.3.3. LWAPP Message Header format over IP/UDP transport . 25
 3.3.4. Fragmentation/Reassembly for IPv4 . . . . . . . . . 26
 3.3.5. Fragmentation/Reassembly for IPv6 . . . . . . . . . 26
 3.3.6. Multiplexing . . . . . . . . . . . . . . . . . . . . 26
 4. LWAPP Packet Definitions . . . . . . . . . . . . . . . . . . 27
 4.1. LWAPP Data Messages . . . . . . . . . . . . . . . . . . 27
 4.2. LWAPP Control Messages Overview . . . . . . . . . . . . 27
 4.2.1. Control Message Format . . . . . . . . . . . . . . . 28
 4.2.2. Message Element Format . . . . . . . . . . . . . . . 30
 4.2.3. Quality of Service . . . . . . . . . . . . . . . . . 31
 5. LWAPP Discovery Operations . . . . . . . . . . . . . . . . . 32
 5.1. Discovery Request . . . . . . . . . . . . . . . . . . . 32
 5.1.1. Discovery Type . . . . . . . . . . . . . . . . . . . 33
 5.1.2. WTP Descriptor . . . . . . . . . . . . . . . . . . . 33
 5.1.3. WTP Radio Information . . . . . . . . . . . . . . . 34
 5.2. Discovery Response . . . . . . . . . . . . . . . . . . . 35
 5.2.1. AC Address . . . . . . . . . . . . . . . . . . . . . 35
 5.2.2. AC Descriptor . . . . . . . . . . . . . . . . . . . 36
 5.2.3. AC Name . . . . . . . . . . . . . . . . . . . . . . 37
 5.2.4. WTP Manager Control IPv4 Address . . . . . . . . . . 37
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 5.2.5. WTP Manager Control IPv6 Address . . . . . . . . . . 38
 5.3. Primary Discovery Request . . . . . . . . . . . . . . . 38
 5.3.1. Discovery Type . . . . . . . . . . . . . . . . . . . 39
 5.3.2. WTP Descriptor . . . . . . . . . . . . . . . . . . . 39
 5.3.3. WTP Radio Information . . . . . . . . . . . . . . . 39
 5.4. Primary Discovery Response . . . . . . . . . . . . . . . 39
 5.4.1. AC Descriptor . . . . . . . . . . . . . . . . . . . 39
 5.4.2. AC Name . . . . . . . . . . . . . . . . . . . . . . 39
 5.4.3. WTP Manager Control IPv4 Address . . . . . . . . . . 40
 5.4.4. WTP Manager Control IPv6 Address . . . . . . . . . . 40
 6. Control Channel Management . . . . . . . . . . . . . . . . . 41
 6.1. Join Request . . . . . . . . . . . . . . . . . . . . . . 41
 6.1.1. WTP Descriptor . . . . . . . . . . . . . . . . . . . 42
 6.1.2. AC Address . . . . . . . . . . . . . . . . . . . . . 42
 6.1.3. WTP Name . . . . . . . . . . . . . . . . . . . . . . 42
 6.1.4. Location Data . . . . . . . . . . . . . . . . . . . 42
 6.1.5. WTP Radio Information . . . . . . . . . . . . . . . 43
 6.1.6. Certificate . . . . . . . . . . . . . . . . . . . . 43
 6.1.7. Session ID . . . . . . . . . . . . . . . . . . . . . 43
 6.1.8. Test . . . . . . . . . . . . . . . . . . . . . . . . 44
 6.1.9. XNonce . . . . . . . . . . . . . . . . . . . . . . . 44
 6.2. Join Response . . . . . . . . . . . . . . . . . . . . . 44
 6.2.1. Result Code . . . . . . . . . . . . . . . . . . . . 45
 6.2.2. Status . . . . . . . . . . . . . . . . . . . . . . . 45
 6.2.3. Certificate . . . . . . . . . . . . . . . . . . . . 46
 6.2.4. WTP Manager Data IPv4 Address . . . . . . . . . . . 46
 6.2.5. WTP Manager Data IPv6 Address . . . . . . . . . . . 47
 6.2.6. AC IPv4 List . . . . . . . . . . . . . . . . . . . . 47
 6.2.7. AC IPv6 List . . . . . . . . . . . . . . . . . . . . 48
 6.2.8. ANonce . . . . . . . . . . . . . . . . . . . . . . . 48
 6.2.9. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 49
 6.3. Join ACK . . . . . . . . . . . . . . . . . . . . . . . . 50
 6.3.1. Session ID . . . . . . . . . . . . . . . . . . . . . 50
 6.3.2. WNonce . . . . . . . . . . . . . . . . . . . . . . . 50
 6.3.3. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 51
 6.4. Join Confirm . . . . . . . . . . . . . . . . . . . . . . 51
 6.4.1. Session ID . . . . . . . . . . . . . . . . . . . . . 51
 6.4.2. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 51
 6.5. Echo Request . . . . . . . . . . . . . . . . . . . . . . 51
 6.6. Echo Response . . . . . . . . . . . . . . . . . . . . . 52
 6.7. Key Update Request . . . . . . . . . . . . . . . . . . . 52
 6.7.1. Session ID . . . . . . . . . . . . . . . . . . . . . 52
 6.7.2. XNonce . . . . . . . . . . . . . . . . . . . . . . . 52
 6.8. Key Update Response . . . . . . . . . . . . . . . . . . 52
 6.8.1. Session ID . . . . . . . . . . . . . . . . . . . . . 53
 6.8.2. ANonce . . . . . . . . . . . . . . . . . . . . . . . 53
 6.8.3. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 53
 6.9. Key Update ACK . . . . . . . . . . . . . . . . . . . . . 53
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 6.9.1. WNonce . . . . . . . . . . . . . . . . . . . . . . . 53
 6.9.2. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 53
 6.10. Key Update Confirm . . . . . . . . . . . . . . . . . . . 53
 6.10.1. PSK-MIC . . . . . . . . . . . . . . . . . . . . . . 54
 6.11. Key Update Trigger . . . . . . . . . . . . . . . . . . . 54
 6.11.1. Session ID . . . . . . . . . . . . . . . . . . . . . 54
 7. WTP Configuration Management . . . . . . . . . . . . . . . . 55
 7.1. Configuration Consistency . . . . . . . . . . . . . . . 55
 7.2. Configure Request . . . . . . . . . . . . . . . . . . . 56
 7.2.1. Administrative State . . . . . . . . . . . . . . . . 56
 7.2.2. AC Name . . . . . . . . . . . . . . . . . . . . . . 57
 7.2.3. AC Name with Index . . . . . . . . . . . . . . . . . 57
 7.2.4. WTP Board Data . . . . . . . . . . . . . . . . . . . 57
 7.2.5. Statistics Timer . . . . . . . . . . . . . . . . . . 58
 7.2.6. WTP Static IP Address Information . . . . . . . . . 59
 7.2.7. WTP Reboot Statistics . . . . . . . . . . . . . . . 59
 7.3. Configure Response . . . . . . . . . . . . . . . . . . . 60
 7.3.1. Decryption Error Report Period . . . . . . . . . . . 61
 7.3.2. Change State Event . . . . . . . . . . . . . . . . . 61
 7.3.3. LWAPP Timers . . . . . . . . . . . . . . . . . . . . 62
 7.3.4. AC IPv4 List . . . . . . . . . . . . . . . . . . . . 62
 7.3.5. AC IPv6 List . . . . . . . . . . . . . . . . . . . . 62
 7.3.6. WTP Fallback . . . . . . . . . . . . . . . . . . . . 63
 7.3.7. Idle Timeout . . . . . . . . . . . . . . . . . . . . 63
 7.4. Configuration Update Request . . . . . . . . . . . . . . 63
 7.4.1. WTP Name . . . . . . . . . . . . . . . . . . . . . . 64
 7.4.2. Change State Event . . . . . . . . . . . . . . . . . 64
 7.4.3. Administrative State . . . . . . . . . . . . . . . . 64
 7.4.4. Statistics Timer . . . . . . . . . . . . . . . . . . 64
 7.4.5. Location Data . . . . . . . . . . . . . . . . . . . 64
 7.4.6. Decryption Error Report Period . . . . . . . . . . . 64
 7.4.7. AC IPv4 List . . . . . . . . . . . . . . . . . . . . 64
 7.4.8. AC IPv6 List . . . . . . . . . . . . . . . . . . . . 64
 7.4.9. Add Blacklist Entry . . . . . . . . . . . . . . . . 64
 7.4.10. Delete Blacklist Entry . . . . . . . . . . . . . . . 65
 7.4.11. Add Static Blacklist Entry . . . . . . . . . . . . . 66
 7.4.12. Delete Static Blacklist Entry . . . . . . . . . . . 66
 7.4.13. LWAPP Timers . . . . . . . . . . . . . . . . . . . . 67
 7.4.14. AC Name with Index . . . . . . . . . . . . . . . . . 67
 7.4.15. WTP Fallback . . . . . . . . . . . . . . . . . . . . 67
 7.4.16. Idle Timeout . . . . . . . . . . . . . . . . . . . . 67
 7.5. Configuration Update Response . . . . . . . . . . . . . 67
 7.5.1. Result Code . . . . . . . . . . . . . . . . . . . . 67
 7.6. Change State Event Request . . . . . . . . . . . . . . . 67
 7.6.1. Change State Event . . . . . . . . . . . . . . . . . 68
 7.7. Change State Event Response . . . . . . . . . . . . . . 68
 7.8. Clear Config Indication . . . . . . . . . . . . . . . . 68
 8. Device Management Operations . . . . . . . . . . . . . . . . 69
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 8.1. Image Data Request . . . . . . . . . . . . . . . . . . . 69
 8.1.1. Image Download . . . . . . . . . . . . . . . . . . . 69
 8.1.2. Image Data . . . . . . . . . . . . . . . . . . . . . 69
 8.2. Image Data Response . . . . . . . . . . . . . . . . . . 70
 8.3. Reset Request . . . . . . . . . . . . . . . . . . . . . 70
 8.4. Reset Response . . . . . . . . . . . . . . . . . . . . . 70
 8.5. WTP Event Request . . . . . . . . . . . . . . . . . . . 71
 8.5.1. Decryption Error Report . . . . . . . . . . . . . . 71
 8.5.2. Duplicate IPv4 Address . . . . . . . . . . . . . . . 71
 8.5.3. Duplicate IPv6 Address . . . . . . . . . . . . . . . 72
 8.6. WTP Event Response . . . . . . . . . . . . . . . . . . . 73
 8.7. Data Transfer Request . . . . . . . . . . . . . . . . . 73
 8.7.1. Data Transfer Mode . . . . . . . . . . . . . . . . . 73
 8.7.2. Data Transfer Data . . . . . . . . . . . . . . . . . 74
 8.8. Data Transfer Response . . . . . . . . . . . . . . . . . 74
 9. Mobile Session Management . . . . . . . . . . . . . . . . . . 75
 9.1. Mobile Config Request . . . . . . . . . . . . . . . . . 75
 9.1.1. Delete Mobile . . . . . . . . . . . . . . . . . . . 75
 9.2. Mobile Config Response . . . . . . . . . . . . . . . . . 76
 9.2.1. Result Code . . . . . . . . . . . . . . . . . . . . 76
 10. LWAPP Security . . . . . . . . . . . . . . . . . . . . . . . 77
 10.1. Securing WTP-AC communications . . . . . . . . . . . . . 77
 10.2. LWAPP Frame Encryption . . . . . . . . . . . . . . . . . 78
 10.3. Authenticated Key Exchange . . . . . . . . . . . . . . . 78
 10.3.1. Terminology . . . . . . . . . . . . . . . . . . . . 79
 10.3.2. Initial Key Generation . . . . . . . . . . . . . . . 80
 10.3.3. Refreshing Cryptographic Keys . . . . . . . . . . . 84
 10.4. Certificate Usage . . . . . . . . . . . . . . . . . . . 85
 11. IEEE 802.11 Binding . . . . . . . . . . . . . . . . . . . . . 86
 11.1. Division of labor . . . . . . . . . . . . . . . . . . . 86
 11.1.1. Split MAC . . . . . . . . . . . . . . . . . . . . . 86
 11.1.2. Local MAC . . . . . . . . . . . . . . . . . . . . . 88
 11.2. Roaming Behavior and 802.11 security . . . . . . . . . . 91
 11.3. Transport specific bindings . . . . . . . . . . . . . . 92
 11.3.1. Status and WLANS field . . . . . . . . . . . . . . . 92
 11.4. BSSID to WLAN ID Mapping . . . . . . . . . . . . . . . . 93
 11.5. Quality of Service . . . . . . . . . . . . . . . . . . . 93
 11.6. Data Message bindings . . . . . . . . . . . . . . . . . 93
 11.7. Control Message bindings . . . . . . . . . . . . . . . . 93
 11.7.1. Mobile Config Request . . . . . . . . . . . . . . . 94
 11.7.2. WTP Event Request . . . . . . . . . . . . . . . . . 100
 11.8. 802.11 Control Messages . . . . . . . . . . . . . . . . 102
 11.8.1. IEEE 802.11 WLAN Config Request . . . . . . . . . . 102
 11.8.2. IEEE 802.11 WLAN Config Response . . . . . . . . . . 107
 11.8.3. IEEE 802.11 WTP Event . . . . . . . . . . . . . . . 107
 11.9. Message Element Bindings . . . . . . . . . . . . . . . . 109
 11.9.1. IEEE 802.11 WTP WLAN Radio Configuration . . . . . . 109
 11.9.2. IEEE 802.11 Rate Set . . . . . . . . . . . . . . . . 111
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 11.9.3. IEEE 802.11 Multi-domain Capability . . . . . . . . 111
 11.9.4. IEEE 802.11 MAC Operation . . . . . . . . . . . . . 112
 11.9.5. IEEE 802.11 Tx Power . . . . . . . . . . . . . . . . 114
 11.9.6. IEEE 802.11 Tx Power Level . . . . . . . . . . . . . 114
 11.9.7. IEEE 802.11 Direct Sequence Control . . . . . . . . 115
 11.9.8. IEEE 802.11 OFDM Control . . . . . . . . . . . . . . 116
 11.9.9. IEEE 802.11 Antenna . . . . . . . . . . . . . . . . 117
 11.9.10. IEEE 802.11 Supported Rates . . . . . . . . . . . . 118
 11.9.11. IEEE 802.11 CFP Status . . . . . . . . . . . . . . . 118
 11.9.12. IEEE 802.11 WTP Mode and Type . . . . . . . . . . . 119
 11.9.13. IEEE 802.11 Broadcast Probe Mode . . . . . . . . . . 119
 11.9.14. IEEE 802.11 WTP Quality of Service . . . . . . . . . 120
 11.9.15. IEEE 802.11 MIC Error Report From Mobile . . . . . . 121
 11.10. IEEE 802.11 Message Element Values . . . . . . . . . . . 122
 12. LWAPP Protocol Timers . . . . . . . . . . . . . . . . . . . . 123
 12.1. MaxDiscoveryInterval . . . . . . . . . . . . . . . . . . 123
 12.2. SilentInterval . . . . . . . . . . . . . . . . . . . . . 123
 12.3. NeighborDeadInterval . . . . . . . . . . . . . . . . . . 123
 12.4. EchoInterval . . . . . . . . . . . . . . . . . . . . . . 123
 12.5. DiscoveryInterval . . . . . . . . . . . . . . . . . . . 123
 12.6. RetransmitInterval . . . . . . . . . . . . . . . . . . . 123
 12.7. ResponseTimeout . . . . . . . . . . . . . . . . . . . . 124
 12.8. KeyLifetime . . . . . . . . . . . . . . . . . . . . . . 124
 13. LWAPP Protocol Variables . . . . . . . . . . . . . . . . . . 125
 13.1. MaxDiscoveries . . . . . . . . . . . . . . . . . . . . . 125
 13.2. DiscoveryCount . . . . . . . . . . . . . . . . . . . . . 125
 13.3. RetransmitCount . . . . . . . . . . . . . . . . . . . . 125
 13.4. MaxRetransmit . . . . . . . . . . . . . . . . . . . . . 125
 14. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 126
 15. Security Considerations . . . . . . . . . . . . . . . . . . . 128
 15.1. Certificate based Session Key establishment . . . . . . 129
 15.2. PSK based Session Key establishment . . . . . . . . . . 129
 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 130
 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 131
 18. IPR Statement . . . . . . . . . . . . . . . . . . . . . . . . 132
 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 133
 19.1. Normative References . . . . . . . . . . . . . . . . . . 133
 19.2. Informational References . . . . . . . . . . . . . . . . 134
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 135
 Intellectual Property and Copyright Statements . . . . . . . . . 137
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1. Introduction
 Unlike wired network elements, Wireless Termination Points (WTPs)
 require a set of dynamic management and control functions related to
 their primary task of connecting the wireless and wired mediums.
 Today, protocols for managing WTPs are either manual static
 configuration via HTTP, proprietary Layer 2 specific or non-existent
 (if the WTPs are self-contained). The emergence of simple 802.11
 WTPs that are managed by a WLAN appliance or switch (also known as an
 Access Controller, or AC) suggests that having a standardized,
 interoperable protocol could radically simplify the deployment and
 management of wireless networks. In many cases the overall control
 and management functions themselves are generic and could apply to an
 AP for any wireless Layer 2 protocol. Being independent of specific
 wireless Layer 2 technologies, such a protocol could better support
 interoperability between Layer 2 devices and enable smoother
 intertechnology handovers.
 The details of how these functions would be implemented are dependent
 on the particular Layer 2 wireless technology. Such a protocol would
 need provisions for binding to specific technologies.
 LWAPP assumes a network configuration that consists of multiple WTPs
 communicating either via layer 2 (MAC) or layer 3 (IP) to an AC. The
 WTPs can be considered as remote RF interfaces, being controlled by
 the AC. The AC forwards all L2 frames it wants to transmit to an WTP
 via the LWAPP protocol. Packets from mobile nodes are forwarded by
 the WTP to the AC, also via this protocol. Figure 1 illustrates this
 arrangement as applied to an IEEE 802.11 binding.
 +-+ 802.11frames +-+
 | |--------------------------------| |
 | | +-+ | |
 | |--------------| |---------------| |
 | | 802.11 PHY/ | | LWAPP | |
 | | MAC sublayer | | | |
 +-+ +-+ +-+
 STA WTP AC
 Figure 1: LWAPP Architecture
 Security is another aspect of Wireless Termination Point management
 that is not well served by existing solutions. Provisioning WTPs
 with security credentials, and managing which WTPs are authorized to
 provide service are today handled by proprietary solutions. Allowing
 these functions to be performed from a centralized AC in an
 interoperable fashion increases managability and allows network
 operators to more tightly control their wireless network
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 infrastructure.
 This document describes the Light Weight Access Point Protocol
 (LWAPP), allowing an AC to manage a collection of WTPs. The protocol
 is defined to be independent of Layer 2 technology, but an 802.11
 binding is provided for use in growing 802.11 wireless LAN networks.
 Goals
 The following are goals for this protocol:
 1. Centralization of the bridging, forwarding, authentication and
 policy enforcement functions for a wireless network. Optionally,
 the AC may also provide centralized encryption of user traffic.
 This will permit reduced cost and higher efficiency when applying
 the capabilities of network processing silicon to the wireless
 network, as it has already been applied to wired LANs.
 2. Permit shifting of the higher level protocol processing burden
 away from the WTP. This leaves the computing resource of the WTP
 to the timing critical applications of wireless control and
 access. This makes the most efficient use of the computing power
 available in WTPs that are the subject of severe cost pressure.
 3. Providing a generic encapsulation and transport mechanism, the
 protocol may be applied to other access point type in the future
 by adding the binding.
 The LWAPP protocol concerns itself solely with the interface between
 the WTP and the AC. Inter-AC, or mobile to AC communication is
 strictly outside the scope of this document.
1.1. Conventions used in this document
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [1].
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2. Protocol Overview
 LWAPP is a generic protocol defining how Wireless Termination Points
 communicate with Access Controllers. Wireless Termination Points and
 Access Controllers may communicate either by means of Layer 2
 protocols or by means of a routed IP network.
 LWAPP messages and procedures defined in this document apply to both
 types of transports unless specified otherwise. Transport
 independence is achieved by defining formats for both MAC level and
 IP level transport (see Section 3). Also defined are framing,
 fragmentation/reassembly, and multiplexing services to LWAPP for each
 transport type.
 The LWAPP Transport layer carries two types of payload. LWAPP Data
 Messages are forwarded wireless frames. LWAPP Control Messages are
 management messages exchanged between an WTP and an AC. The LWAPP
 transport header defines the "C-bit", which is used to distinguish
 data and control traffic. When used over IP, the LWAPP data and
 control traffic are also sent over separate UDP ports. Since both
 data and control frames can exceed PMTU, the payload of an LWAPP data
 or control message can be fragmented. The fragmentation behavior is
 highly dependent upon the lower layer transport and is defined in
 Section 3.
 The Light Weight Access Protocol (LWAPP) begins with a discovery
 phase. The WTPs send a Discovery Request frame, causing any Access
 Controller (AC) , receiving that frame to respond with a Discovery
 Response. From the Discovery Responses received, an WTP will select
 an AC with which to associate, using the Join Request and Join
 Response. The Join Request also provides an MTU discovery mechanism,
 to determine whether there is support for the transport of large
 frames between the WTP and it's AC. If support for large frames is
 not present, the LWAPP frames will be fragmented to the maximum
 length discovered to be supported by the network.
 Once the WTP and the AC have joined, a configuration exchange is
 accomplished that will cause both devices to agree on version
 information. During this exchange the WTP may receive provisioning
 settings. For the 802.11 binding, this information would typically
 include a name (802.11 Service Set Identifier, SSID), and security
 parameters, the data rates to be advertised as well as the radio
 channel (channels, if the WTP is capable of operating more than one
 802.11 MAC and PHY simultaneously) to be used. Finally, the WTPs are
 enabled for operation.
 When the WTP and AC have completed the version and provision exchange
 and the WTP is enabled, the LWAPP encapsulates the wireless frames
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 sent between them. LWAPP will fragment its packets, if the size of
 the encapsulated wireless user data (Data) or protocol control
 (Management) frames causes the resultant LWAPP packet to exceed the
 MTU supported between the WTP and AC. Fragmented LWAPP packets are
 reassembled to reconstitute the original encapsulated payload.
 In addition to the functions thus far described, LWAPP also provides
 for the delivery of commands from the AC to the WTP for the
 management of devices that are communicating with the WTP. This may
 include the creation of local data structures in the WTP for the
 managed devices and the collection of statistical information about
 the communication between the WTP and the 802.11 devices. LWAPP
 provides the ability for the AC to obtain any statistical information
 collected by the WTP.
 LWAPP also provides for a keep alive feature that preserves the
 communication channel between the WTP and AC. If the AC fails to
 appear alive, the WTP will try to discover a new AC to communicate
 through.
 This Document uses terminology defined in [5]
2.1. Wireless Binding Definition
 This draft standard specifies a protocol independent of a specific
 wireless access point radio technology. Elements of the protocol are
 designed to accommodate specific needs of each wireless technology in
 a standard way. Implementation of this standard for a particular
 wireless technology must follow the binding requirements defined for
 that technology. This specification includes a binding for the IEEE
 802.11 (see Section 11).
 When defining a binding for other technologies, the authors MUST
 include any necessary definitions for technology-specific messages
 and all technology-specific message elements for those messages. At
 a minimum, a binding MUST provide the definition for a binding-
 specific Statistics message element, which is carried in the WTP
 Event Request message, and Add Mobile message element, which is
 carried in the Mobile Configure Request. If any technology specific
 message elements are required for any of the existing LWAPP messages
 defined in this specification, they MUST also be defined in the
 technology binding document.
 The naming of binding-specific message elements MUST begin with the
 name of the technology type, e.g., the binding for IEEE 802.11,
 provided in this standard, begins with "IEEE 802.11"."
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2.2. LWAPP State Machine Definition
 The following state diagram represents the lifecycle of an WTP-AC
 session:
 /-------------\
 | v
 | +------------+
 | C| Idle |<-----------------------------------\
 | +------------+<-----------------------\ |
 | ^ |a ^ | |
 | | | \----\ | |
 | | | | +------------+ |
 | | | | -------| Key Confirm| |
 | | | | w/ +------------+ |
 | | | | | ^ |
 | | | |t V |5 |
 | | | +-----------+ +------------+ |
 | / | C| Run | | Key Update | |
 | / | r+-----------+------>+------------+ |
 | / | ^ |s u x| |
 | | v | | | |
 | | +--------------+ | | v |y
 | | C| Discovery | q| \--------------->+-------+
 | | b+--------------+ +-------------+ | Reset |
 | | |d f| ^ | Configure |------->+-------+
 | | | | | +-------------+p ^
 | |e v | | ^ |
 | +---------+ v |i 2| |
 | C| Sulking | +------------+ +--------------+ |
 | +---------+ C| Join |--->| Join-Confirm | |
 | g+------------+z +--------------+ |
 | |h m| 3| |4 |
 | | | | v |o
 |\ | | | +------------+
 \\-----------------/ \--------+---->| Image Data |C
 \------------------------------------/ +------------+n
 Figure 2: LWAPP State Machine
 The LWAPP state machine, depicted above, is used by both the AC and
 the WTP. For every state defined, only certain messages are
 permitted to be sent and received. In all of the LWAPP control
 messages defined in this document, the state for which each command
 is valid is specified.
 Note that in the state diagram figure above, the 'C' character is
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 used to represent a condition that causes the state to remain the
 same.
 The following text discusses the various state transitions, and the
 events that cause them.
 Idle to Discovery (a): This is the initialization state.
 WTP: The WTP enters the Discovery state prior to transmitting the
 first Discovery Request (see Section 5.1). Upon entering this
 state, the WTP sets the DiscoveryInterval timer (see
 Section 12). The WTP resets the DiscoveryCount counter to zero
 (0) (see Section 13). The WTP also clears all information from
 ACs (e.g., AC Addresses) it may have received during a previous
 Discovery phase.
 AC: The AC does not need to maintain state information for the
 WTP upon reception of the Discovery Request, but it MUST
 respond with a Discovery Response (see Section 5.2).
 Discovery to Discovery (b): This is the state the WTP uses to
 determine which AC it wishes to connect to.
 WTP: This event occurs when the DiscoveryInterval timer expires.
 The WTP transmits a Discovery Request to every AC which the WTP
 hasn't received a response to. For every transition to this
 event, the WTP increments DisoveryCount counter. See
 Section 5.1) for more information on how the WTP knows which
 ACs it should transmit the Discovery Requests to. The WTP
 restarts the DiscoveryInterval timer.
 AC: This is a noop.
 Discovery to Sulking (d): This state occurs on a WTP when Discovery
 or connectivity to the AC fails.
 WTP: The WTP enters this state when the DiscoveryInterval timer
 expires and the DiscoveryCount variable is equal to the
 MaxDiscoveries variable (see Section 13). Upon entering this
 state, the WTP will start the SilentInterval timer. While in
 the Sulking state, all LWAPP messages received are ignored.
 AC: This is a noop.
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 Sulking to Idle (e): This state occurs on a WTP when it must restart
 the discovery phase.
 WTP: The WTP enters this state when the SilentInterval timer (see
 Section 12) expires.
 AC: This is a noop.
 Discovery to Join (f): This state is used by the WTP to confirm its
 commitment to an AC that it wishes to be provided service.
 WTP: The WTP selects the best AC based on the information it
 gathered during the Discovery Phase. It then transmits a Join
 Request (see Section 6.1 to its preferred AC. The WTP starts
 the WaitJoin Timer (see Section 12).
 AC: The AC enters this state for the given WTP upon reception of
 a Join Request. The AC processes the request and responds with
 a Join Response.
 Join to Join (g): This state transition occurs during the join
 phase.
 WTP: The WTP enters this state when the WaitJoin timer expires,
 and the underlying transport requires LWAPP MTU detection
 Section 3).
 AC: This state occurs when the AC receives a retransmission of a
 Join Request. The WTP processes the request and responds with
 the Join Response..
 Join to Idle (h): This state is used when the join process failed.
 WTP: This state transition occurs if the WTP is configured to use
 PSK security and receives a Join Response that includes an
 invalid PSK-MIC message element.
 AC: The AC enters this state when it transmits an unsuccessful
 Join Response.
 Join to Discovery (i): This state is used when the join process
 failed.
 WTP: The WTP enters this state when it receives an unsuccessful
 Join Response. Upon entering this state, the WTP sets the
 DiscoveryInterval timer (see Section 12). The WTP resets the
 DiscoveryCount counter to zero (0) (see Section 13). This
 state transition may also occur if the PSK-MIC (see
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 Section 6.2.9) message element is invalid.
 AC: This state transition is invalid.
 Join to Join-Confirm (z): This state is used to provide key
 confirmation during the join process.
 WTP: This state is entered when the WTP receives a Join Response.
 In the event that certificate based security is utilized, this
 transition will occur if the Certificate message element is
 present and valid in the Join Response. For pre-shared key
 security, the Join Response must include a valud and
 authenticated PSK-MIC message element. The WTP MUST respond
 with a Join ACK, which is used to provide key confirmation.
 AC: The AC enters this state when it receives a valid Join ACK.
 For certificate based security, the Join ACK MUST include a
 valid and authenticated xxxx message element. For pre-shared
 key security, the message must include a valid PSK-MIC message
 element. The AC MUST respond with a Join Confirm message,
 which includes the Session Key message element.
 Join-Confirm to Idle (3): This state is used when the join process
 failed.
 WTP: This state transition occurs when the WTP receives an
 invalid Join Confirm.
 AC: The AC enters this state when it receives an invalid Join
 ACK.
 Join-Confirm to Configure (2): This state is used by the WTP and the
 AC to exchange configuration information.
 WTP: The WTP enters this state when it receives a successful Join
 Confirm, and determines that its version number and the version
 number advertised by the AC are the same. The WTP transmits
 the Configure Request (see Section 7.2) message to the AC with
 a snapshot of its current configuration. The WTP also starts
 the ResponseTimeout timer (see Section 12).
 AC: This state transition occurs when the AC receives the
 Configure Request from the WTP. The AC must transmit a
 Configure Response (see Section 7.3) to the WTP, and may
 include specific message elements to override the WTP's
 configuration.
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 Join-Confirm to Image Data (4): This state is used by the WTP and
 the AC to download executable firmware.
 WTP: The WTP enters this state when it receives a successful Join
 Confirm, and determines that its version number and the version
 number advertised by the AC are different. The WTP transmits
 the Image Data Request (see Section 8.1) message requesting
 that the AC's latest firmware be initiated.
 AC: This state transition occurs when the AC receives the Image
 Data Request from the WTP. The AC must transmit a Image Data
 Response (see Section 8.2) to the WTP, which includes a portion
 of the firmware.
 Image Data to Image Data (n): This state is used by WTP and the AC
 during the firmware download phase.
 WTP: The WTP enters this state when it receives a Image Data
 Response that indicates that the AC has more data to send.
 AC: This state transition occurs when the AC receives the Image
 Data Request from the WTP while already in this state, and it
 detects that the firmware download has not completed.
 Image Data to Reset (o): This state is used when the firmware
 download is completed.
 WTP: The WTP enters this state when it receives a Image Data
 Response that indicates that the AC has no more data to send,
 or if the underlying LWAPP transport indicates a link failure.
 At this point, the WTP reboots itself.
 AC: This state transition occurs when the AC receives the Image
 Data Request from the WTP while already in this state, and it
 detects that the firmware download has completed, or if the
 underlying LWAPP transport indicates a link failure. Note that
 the AC itself does not reset, but it places the specific WTPs
 context it is communicating with in the reset state, meaning
 that it clears all state associated with the WTP.
 Configure to Reset (p): This state transition occurs if the
 Configure phase fails.
 WTP: The WTP enters this state when the reliable transport fails
 to deliver the Configure Request, or if the ResponseTimeout
 Timer (see Section 12)expires.
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 AC: This state transition occurs if the AC is unable to transmit
 the Configure Response to a specific WTP. Note that the AC
 itself does not reset, but it places the specific WTPs context
 it is communicating with in the reset state, meaning that it
 clears all state associated with the WTP.
 Configure to Run (q): This state transition occurs when the WTP and
 AC enters their normal state of operation.
 WTP: The WTP enters this state when it receives a successful
 Configure Response from the AC. The WTP initializes the
 HeartBeat Timer (see Section 12), and transmits the Change
 State Event Request message (see Section 7.6).
 AC: This state transition occurs when the AC receives the Change
 State Event Request (see Section 7.6) from the WTP. The AC
 responds with a Change State Event Response (see Section 7.7)
 message. The AC must start the Session ID and Neighbor Dead
 timers (see Section 12).
 Run to Run (r): This is the normal state of operation.
 WTP: This is the WTP's normal state of operation, and there are
 many events that cause this to occur:
 Configuration Update: The WTP receives a Configuration Update
 Request (see Section 7.4). The WTP MUST respond with a
 Configuration Update Response (see Section 7.5).
 Change State Event: The WTP receives a Change State Event
 Response, or determines that it must initiate a Change State
 Event Request, as a result of a failure or change in the
 state of a radio.
 Echo Request: The WTP receives an Echo Request message
 Section 6.5), which it MUST respond with an Echo Response
 (see Section 6.6).
 Clear Config Indication: The WTP receives a Clear Config
 Indication message Section 7.8). The WTP MUST reset its
 configuration back to manufacturer defaults.
 WTP Event: The WTP generates a WTP Event Request to send
 information to the AC Section 8.5). The WTP receives a WTP
 Event Response from the AC Section 8.6).
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 Data Transfer: The WTP generates a Data Transfer Request to
 the AC Section 8.7). The WTP receives a Data Transfer
 Response from the AC Section 8.8).
 WLAN Config Request: The WTP receives an WLAN Config Request
 message Section 11.8.1), which it MUST respond with an WLAN
 Config Response (see Section 11.8.2).
 Mobile Config Request: The WTP receives an Mobile Config
 Request message Section 9.1), which it MUST respond with an
 Mobile Config Response (see Section 9.2).
 AC: This is the AC's normal state of operation, and there are
 many events that cause this to occur:
 Configuration Update: The AC sends a Configuration Update
 Request (see Section 7.4) to the WTP to update its
 configuration. The AC receives a Configuration Update
 Response (see Section 7.5) from the WTP.
 Change State Event: The AC receives a Change State Event
 Request (see Section 7.6), which it MUST respond to with the
 Change State Event Response (see Section 7.7).
 Echo: The AC sends an Echo Request message Section 6.5) or
 receives the associated Echo Response (see Section 6.6) from
 the WTP.
 Clear Config Indication: The AC sends a Clear Config
 Indication message Section 7.8).
 WLAN Config: The AC sends an WLAN Config Request message
 Section 11.8.1) or receives the associated WLAN Config
 Response (see Section 11.8.2) from the WTP.
 Mobile Config: The AC sends an Mobile Config Request message
 Section 9.1) or receives the associated Mobile Config
 Response (see Section 9.2) from the WTP.
 Data Transfer: The AC receives a Data Transfer Request from
 the AC (see Section 8.7) and MUST generate the associated
 Data Transfer Response message (see Section 8.8).
 WTP Event: The AC receives a WTP Event Request from the AC
 (see Section 8.5) and MUST generate the associated WTP Event
 Response message (see Section 8.6).
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 Run to Reset (s): This event occurs when the AC wishes for the WTP
 to reboot.
 WTP: The WTP enters this state when it receives a Reset Request
 (see Section 8.3). It must respond with a Reset Response (see
 Section 8.4), and once the reliable transport acknowledgement
 has been received, it must reboot itself.
 AC: This state transition occurs either through some
 administrative action, or via some internal event on the AC
 that causes it to request that the WTP disconnect. Note that
 the AC itself does not reset, but it places the specific WTPs
 context it is communicating with in the reset state.
 Run to Idle (t): This event occurs when an error occurs in the
 communication between the WTP and the AC.
 WTP: The WTP enters this state when the underlying reliable
 transport in unable to transmit a message within the
 RetransmitInterval timer (see Section 12), and the maximum
 number of RetransmitCount counter has reached the MaxRetransmit
 variable (see Section 13).
 AC: The AC enters this state when the underlying reliable
 transport in unable to transmit a message within the
 RetransmitInterval timer (see Section 12), and the maximum
 number of RetransmitCount counter has reached the MaxRetransmit
 variable (see Section 13).
 Run to Key Update (u): This event occurs when the WTP and the AC are
 to exchange new keying material, with which it must use to protect
 all future messages.
 WTP: This state transition occurs when the KeyLifetime timer
 expires (see Section 12).
 AC: The WTP enters this state when it receives a Key Update
 Request (see Section 6.7).
 Key Update to Key Confirm (w): This event occurs during the rekey
 phase and is used to complete the loop.
 WTP: This state transition occurs when the WTP receives the Key
 Update Response. The WTP MUST only accept the message if it is
 authentic. The WTP responds to this response with a Key Update
 ACK.
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 AC: The AC enters this state when it receives an authenticated
 Key Update ACK message.
 Key Confirm to Run (5): This event occurs when the rekey exchange
 phase is completed.
 WTP: This state transition occurs when the WTP receives the Key
 Update Confirm. The newly derived encryption key and IV must
 be plumbed into the crypto module after validating the
 message's authentication.
 AC: The AC enters this state when it transmits the Key Update
 Confirm message. The newly derived encryption key and IV must
 be plumbed into the crypto module after transmitting a Key
 Update Confirm message.
 Key Update to Reset (x): This event occurs when the key exchange
 phase times out.
 WTP: This state transition occurs when the WTP does not receive a
 Key Update Response from the AC.
 AC: The AC enters this state when it is unable to process a Key
 Update Request.
 Reset to Idle (y): This event occurs when the state machine is
 restarted.
 WTP: The WTP reboots itself. After reboot the WTP will start its
 LWAPP state machine in the Idle state.
 AC: The AC clears out any state associated with the WTP. The AC
 generally does this as a result of the reliable link layer
 timing out.
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3. LWAPP Transport Layers
 The LWAPP protocol can operate at layer 2 or 3. For layer 2 support,
 the LWAPP messages are carried in a native Ethernet frame. As such,
 the protocol is not routable and depends upon layer 2 connectivity
 between the WTP and the AC. Layer 3 support is provided by
 encapsulating the LWAPP messages within UDP.
3.1. LWAPP Transport Header
 All LWAPP protocol packets are encapsulated using a common header
 format, regardless of the transport used to carry the frames.
 However, certain flags are not applicable for a given transport, and
 it is therefore necessary to refer to the specific transport section
 in order to determine which flags are valid.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |VER| RID |C|F|L| Frag ID | Length |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Status/WLANs | Payload... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.1.1. VER Field
 A 2 bit field which contains the version of LWAPP used in this
 packet. The value for this draft is 0.
3.1.2. RID Field
 A 3 bit field which contains the Radio ID number for this packet.
 WTPs with multiple radios but a single MAC Address use this field to
 indicate which radio is associated with the packet.
3.1.3. C Bit
 The Control Message 'C' bit indicates whether this packet carries a
 data or control message. When this bit is zero (0), the packet
 carries an LWAPP data message in the payload (see Section 4.1). When
 this bit is one (1), the packet carries an LWAPP control message as
 defined in section Section 4.2 for consumption by the addressed
 destination.
3.1.4. F Bit
 The Fragment 'F' bit indicates whether this packet is a fragment.
 When this bit is one (1), the packet is a fragment and MUST be
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 combined with the other corresponding fragments to reassemble the
 complete information exchanged between the WTP and AC.
3.1.5. L Bit
 The Not Last 'L' bit is valid only if the 'F' bit is set and
 indicates whether the packet contains the last fragment of a
 fragmented exchange between WTP and AC. When this bit is 1, the
 packet is not the last fragment. When this bit is 0, the packet is
 the last fragment.
3.1.6. Fragment ID
 An 8 bit field whose value is assigned to each group of fragments
 making up a complete set. The fragment ID space is managed
 individually for every WTP/AC pair. The value of Fragment ID is
 incremented with each new set of fragments. The Fragment ID wraps to
 zero after the maximum value has been used to identify a set of
 fragments. LWAPP only supports up to 2 fragments per frame.
3.1.7. Length
 The 16 bit length field contains the number of bytes in the Payload.
 The field is encoded as an unsigned number. If the LWAPP packet is
 encrypted, the length field includes the AES-CCM MIC (see
 Section 10.2 for more information).
3.1.8. Status and WLANS
 The interpretation of this 16 bit field is binding specific. Refer
 to the transport portion of the binding for a wireless technology for
 the specification.
3.1.9. Payload
 This field contains the header for an LWAPP Data Message or LWAPP
 Control Message, followed by the data associated with that message.
3.2. Using IEEE 802.3 MAC as LWAPP transport
 This section describes how the LWAPP protocol is provided over native
 ethernet frames. An LWAPP packet is formed from the MAC frame header
 followed by the LWAPP message header. The following figure provides
 an example of the frame formats used when LWAPP is used over the IEEE
 802.3 transport.
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 Layer 2 LWAPP Data Frame
 +-----------------------------------------------------------+
 | MAC Header | LWAPP Header [C=0] | Forwarded Data ... |
 +-----------------------------------------------------------+
 Layer 2 LWAPP Control Frame
 +---------------------------------------------------+
 | MAC Header | LWAPP Header [C=1] | Control Message |
 +---------------------------------------------------+
 | Message Elements ... |
 +----------------------+
3.2.1. Framing
 Source Address
 A MAC address belonging to the interface from which this message is
 sent. If multiple source addresses are configured on an interface,
 then the one chosen is implementation dependent.
 Destination Address
 A MAC address belonging to the interface to which this message is to
 be sent. This destination address MAY be either an individual
 address or a multicast address, if more than one destination
 interface is intended.
 Ethertype
 The Ethertype field is set to 0x88bb.
3.2.2. AC Discovery
 When run over IEEE 802.3, LWAPP messages are distributed to a
 specific MAC level broadcast domain. The AC discovery mechanism used
 with this transport is for an WTP to transmit a Discovery Request
 message to a broadcast destination MAC address. The ACs will receive
 this message and reply based on their policy.
3.2.3. LWAPP Message Header format over IEEE 802.3 MAC transport
 All of the fields described in Section 3.1 are used when LWAPP uses
 the IEEE 802.3 MAC transport.
3.2.4. Fragmentation/Reassembly
 Fragmentation at the MAC layer is managed using the F,L and Frag ID
 fields of the LWAPP message header. The LWAPP protocol only allows a
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 single packet to be fragmented into 2, which is sufficient for a
 frame that exceeds MTU due to LWAPP encapsulation. When used with
 layer 2 (Ethernet) transport, both fragments MUST include the LWAPP
 header.
3.2.5. Multiplexing
 LWAPP control messages and data messages are distinguished by the C
 Bit in the LWAPP message header.
3.3. Using IP/UDP as LWAPP transport
 This section defines how LWAPP makes use of IP/UDP transport between
 the WTP and the AC. When this transport is used, the MAC layer is
 controlled by the IP stack, and there are therefore no special MAC
 layer requirements. The following figure provides an example of the
 frame formats used when LWAPP is used over the IP/UDP transport. IP
 stacks can be either IPv4 or IPv6.
 Layer 3 LWAPP Data Frame
 +--------------------------------------------+
 | MAC Header | IP | UDP | LWAPP Header [C=0] |
 +--------------------------------------------+
 |Forwarded Data ... |
 +-------------------+
 Layer 3 LWAPP Control Frame
 +--------------------------------------------+
 | MAC Header | IP | UDP | LWAPP Header [C=1] |
 +--------------------------------------------+
 | Control Message | Message Elements ... |
 +-----------------+----------------------+
3.3.1. Framing
 Communication between WTP and AC is established according to the
 standard UDP client/server model. The connection is initiated by the
 WTP (client) to the well-known UDP port of the AC (server) used for
 control messages. This UDP port number of the AC is 12222 for LWAPP
 data and 12223 for LWAPP control frames.
3.3.2. AC Discovery
 When LWAPP is run over routed IP networks, the WTP and the AC do not
 need to reside in the same IP subnet (broadcast domain). However, in
 the event the peers reside on separate subnets, there must exist a
 mechanism for the WTP to discover the AC.
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 As the WTP attempts to establish communication with the AC, it sends
 the Discovery Request message and receives the corresponding response
 message from the AC. The WTP must send the Discovery Request message
 to either the limited broadcast IP address (255.255.255.255), a well
 known multicast address or to the unicast IP address of the AC. Upon
 receipt of the message, the AC issues a Discovery Response message to
 the unicast IP address of the WTP, regardless of whether Discovery
 Request was sent as a broadcast, multicast or unicast message.
 Whether the WTP uses a limited IP broadcast, multicast or unicast IP
 address is implementation dependent.
 In order for a WTP to transmit a Discovery Request to a unicast
 address, the WTP must first obtain the IP address of the AC. Any
 static configuration of an AC's IP address on the WTP non-volatile
 storage is implementation dependent. However, additional dynamic
 schemes are possible, for example:
 DHCP: A comma delimited ASCII encoded list of AC IP addresses is
 embedded inside a DHCP vendor specific option 43 extension. An
 example of the actual format of the vendor specific payload for
 IPv4 is of the form "10.1.1.1, 10.1.1.2".
 DNS: The DNS name "LWAPP-AC-Address" MAY be resolvable to or more AC
 addresses
3.3.3. LWAPP Message Header format over IP/UDP transport
 All of the fields described in Section 3.1 are used when LWAPP uses
 the IPv4/UDP or IPv6/UDP transport, with the following exceptions:
3.3.3.1. F Bit
 This flag field is not used with this transport, and MUST be set to
 zero.
3.3.3.2. L Bit
 This flag field is not used with this transport, and MUST be set to
 zero.
3.3.3.3. Frag ID
 This field is not used with this transport, and MUST be set to zero.
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3.3.4. Fragmentation/Reassembly for IPv4
 When LWAPP is implemented at L3, the transport layer uses IP
 fragmentation to fragment and reassemble LWAPP messages that are
 longer than MTU size used by either WTP or AC. The details of IP
 fragmentation are covered in [8]. When used with the IP transport,
 only the first fragment would include the LWAPP header
 [ed: IP fragmentation may raise security concerns and bring
 additional configuration requirements for certain firewalls and NATs.
 One alternative is to re-use the layer 2 (application layer)
 fragmentation reassembly. Comments are welcomed.]
3.3.5. Fragmentation/Reassembly for IPv6
 IPv6 does MTU discovery so fragmentation and re-assembly is not
 necessary for UDP packets.
3.3.6. Multiplexing
 LWAPP messages convey control information between WTP and AC, as well
 as binding specific data frames or binding specific management
 frames. As such, LWAPP messages need to be multiplexed in the
 transport sub-layer and be delivered to the proper software entities
 in the endpoints of the protocol. However, the 'C' bit is still used
 to differentiate between data and control frames.
 In case of Layer 3 connection, multiplexing is achieved by use of
 different UDP ports for control and data packets (see Section 3.3.1.
 As part of Join procedure, the WTP and AC may negotiate different IP
 Addresses for data or control messages. The IP Address returned in
 the AP Manager Control IP Address message element is used to inform
 the WTP with the IP address to which it must sent all control frames.
 The AP Manager Data IP Address message element MAY be present only if
 the AC has a different IP Address which the WTP is to use to send its
 data LWAPP frames.
 In the event the WTP and AC are separated by a NAT, with the WTP
 using private IP address space, it is the responsibility of the NAT
 to manage appropriate UDP port mapping.
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4. LWAPP Packet Definitions
 This section contains the packet types and format. The LWAPP
 protocol is designed to be transport agnostic by specifying packet
 formats for both MAC frames and IP packets. An LWAPP packet consists
 of an LWAPP Transport Layer packet header followed by an LWAPP
 message.
 Transport details can be found in Section 3.
4.1. LWAPP Data Messages
 An LWAPP data message is a forwarded wireless frame. When forwarding
 wireless frames, the sender simply encapsulates the wireless frame in
 an LWAPP data packet, using the appropriate transport rules defined
 in section Section 3.
 In the event that the encapsulated frame would exceed the transport
 layer's MTU, the sender is responsible for the fragmentation of the
 frame, as specified in the transport specific section of Section 3.
 The actual format of the encapsulated LWAPP data frame is subject to
 the rules defined under the specific wireless technology binding.
4.2. LWAPP Control Messages Overview
 The LWAPP Control protocol provides a control channel between the WTP
 and the AC. The control channel is the series of control messages
 between the WTP and AC, associated with a session ID and key.
 Control messages are divided into the following distinct message
 types:
 Discovery: LWAPP Discovery messages are used to identify potential
 ACs, their load and capabilities.
 Control Channel Management: Messages that fall within this
 classification are used for the discovery of ACs by the WTPs as
 well as the establishment and maintenance of an LWAPP control
 channel.
 WTP Configuration: The WTP Configuration messages are used by the AC
 to push a specific configuration to the WTPs it has a control
 channel with. Messages that deal with the retrieval of statistics
 from the WTP also fall in this category.
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 Mobile Session Management: Mobile session management messages are
 used by the AC to push specific mobile policies to the WTP.
 Firmware Management: Messages in this category are used by the AC to
 push a new firmware image down to the WTP.
 Control Channel, WTP Configuration and Mobile Session Management MUST
 be implemented. Firmware Management MAY be implemented.
 In addition, technology specific bindings may introduce new control
 channel commands that depart from the above list.
4.2.1. Control Message Format
 All LWAPP control messages are sent encapsulated within the LWAPP
 header (see Section 3.1). Immediately following the header, is the
 LWAPP control header, which has the following format:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Message Type | Seq Num | Msg Element Length |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Session ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Msg Element [0..N] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2.1.1. Message Type
 The Message Type field identifies the function of the LWAPP control
 message. The valid values for Message Type are the following:
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 Description Value
 Discovery Request 1
 Discovery Response 2
 Join Request 3
 Join Response 4
 Join ACK 5
 Join Confirm 6
 Unused 7-9
 Configure Request 10
 Configure Response 11
 Configuration Update Request 12
 Configuration Update Response 13
 WTP Event Request 14
 WTP Event Response 15
 Change State Event Request 16
 Change State Event Response 17
 Unused 18-21
 Echo Request 22
 Echo Response 23
 Image Data Request 24
 Image Data Response 25
 Reset Request 26
 Reset Response 27
 Unused 28-29
 Key Update Request 30
 Key Update Response 31
 Primary Discovery Request 32
 Primary Discovery Response 33
 Data Transfer Request 34
 Data Transfer Response 35
 Clear Config Indication 36
 WLAN Config Request 37
 WLAN Config Response 38
 Mobile Config Request 39
 Mobile Config Response 40
4.2.1.2. Sequence Number
 The Sequence Number Field is an identifier value to match request/
 response packet exchanges. When an LWAPP packet with a request
 message type is received, the value of the sequence number field is
 copied into the corresponding response packet.
 When an LWAPP control frame is sent, its internal sequence number
 counter is monotonically incremented, ensuring that no two requests
 pending have the same sequence number. This field will wrap back to
 zero.
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4.2.1.3. Message Element Length
 The Length field indicates the number of bytes following the Session
 ID field. If the LWAPP packet is encrypted, the length field
 includes the AES-CCM MIC (see Section 10.2 for more information).
4.2.1.4. Session ID
 The Session ID is a 32-bit unsigned integer that is used to identify
 the security context for encrypted exchanges between the WTP and the
 AC. Note that a Session ID is a random value that MUST be unique
 between a given AC and any of the WTP it may be communicating with.
4.2.1.5. Message Element[0..N]
 The message element(s) carry the information pertinent to each of the
 control message types. Every control message in this specification
 specifies which message elements are permitted.
4.2.2. Message Element Format
 The message element is used to carry information pertinent to a
 control message. Every message element is identified by the Type
 field, whose numbering space is managed via IANA (see Section 16).
 The total length of the message elements is indicated in the Message
 Element Length field.
 All of the message element definitions in this document use a diagram
 similar to the one below in order to depict its format. Note that in
 order to simplify this specification, these diagrams do not include
 the header fields (Type and Length). However, in every message
 element description, the header's fields values will be defined.
 Note that additional message elements may be defined in separate IETF
 documents.
 The format of a message element uses the TLV format shown here:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Type | Length | Value ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Where Type (8 bit) identifies the character of the information
 carried in the Value field and Length (16 bits) indicates the number
 of bytes in the Value field.
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4.2.2.1. Generic Message Elements
 This section includes message elements that are not bound to a
 specific control message.
4.2.2.1.1. Vendor Specific
 The Vendor Specific Payload is used to communicate vendor specific
 information between the WTP and the AC. The value contains the
 following format:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Vendor Identifier |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Element ID | Value... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 104 for Vendor Specific
 Length: >= 7
 Vendor Identifier: A 32-bit value containing the IANA assigned "SMI
 Network Management Private Enterprise Codes" [13]
 Element ID: A 16-bit Element Identifier which is managed by the
 vendor.
 Value: The value associated with the vendor specific element.
4.2.3. Quality of Service
 It is recommended that LWAPP control messages be sent by both the AC
 and the WTP with an appropriate Quality of Service precedence value,
 ensuring that congestion in the network minimizes occurences of LWAPP
 control channel disconnects. Therefore, a Quality of Service enabled
 LWAPP device should use:
 802.1P: The precedence value of 7 SHOULD be used.
 DSCP: The dscp tag value of 46 SHOULD be used.
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5. LWAPP Discovery Operations
 The Discovery messages are used by an WTP to determine which ACs are
 available to provide service, as well as the capabilities and load of
 the ACs.
5.1. Discovery Request
 The Discovery Request is used by the WTP to automatically discover
 potential ACs available in the network. An WTP must transmit this
 command even if it has a statically configured AC, as it is a
 required step in the LWAPP state machine.
 Discovery Requests MUST be sent by an WTP in the Discover state after
 waiting for a random delay less than MaxDiscoveryInterval, after an
 WTP first comes up or is (re)initialized. An WTP MUST send no more
 than a maximum of MaxDiscoveries discoveries, waiting for a random
 delay less than MaxDiscoveryInterval between each successive
 discovery.
 This is to prevent an explosion of WTP Discoveries. An example of
 this occurring would be when many WTPs are powered on at the same
 time.
 Discovery requests MUST be sent by an WTP when no echo responses are
 received for NeighborDeadInterval and the WTP returns to the Idle
 state. Discovery requests are sent after NeighborDeadInterval, they
 MUST be sent after waiting for a random delay less than
 MaxDiscoveryInterval. An WTP MAY send up to a maximum of
 MaxDiscoveries discoveries, waiting for a random delay less than
 MaxDiscoveryInterval between each successive discovery.
 If a discovery response is not received after sending the maximum
 number of discovery requests, the WTP enters the Sulking state and
 MUST wait for an interval equal to SilentInterval before sending
 further discovery requests.
 The Discovery Request message may be sent as a unicast, broadcast or
 multicast message.
 Upon receiving a discovery request, the AC will respond with a
 Discovery Response sent to the address in the source address of the
 received discovery request.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
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5.1.1. Discovery Type
 The Discovery message element is used to configure an WTP to operate
 in a specific mode.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Discovery Type|
 +-+-+-+-+-+-+-+-+
 Type: 58 for Discovery Type
 Length: 1
 Discovery Type: An 8-bit value indicating how the AC was
 discovered. The following values are supported:
 0 - Broadcast
 1 - Configured
5.1.2. WTP Descriptor
 The WTP descriptor message element is used by the WTP to communicate
 it's current hardware/firmware configuration. The value contains the
 following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Hardware Version |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Software Version |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Boot Version |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Max Radios | Radios in use | Encryption Capabilities |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 3 for WTP Descriptor
 Length: 16
 Hardware Version: A 32-bit integer representing the WTP's hardware
 version number
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 Software Version: A 32-bit integer representing the WTP's Firmware
 version number
 Boot Version: A 32-bit integer representing the WTP's boot loader's
 version number
 Max Radios: An 8-bit value representing the number of radios (where
 each radio is identified via the RID field) supported by the WTP
 Radios in use: An 8-bit value representing the number of radios
 present in the WTP
 Encryption Capabilities: This 16-bit field is used by the WTP to
 communicate it's capabilities to the AC. Since most WTPs support
 link layer encryption, the AC may make use of these services.
 There are binding dependent encryption capabilites. An WTP that
 does not have any encryption capabilities would set this field to
 zero (0). Refer to the specific binding for the specification.
5.1.3. WTP Radio Information
 The WTP radios information message element is used to communicate the
 radio information in a specific slot. The Discovery Request MUST
 include one such message element per radio in the WTP. The Radio-
 Type field is used by the AC in order to determine which technology
 specific binding is to be used with the WTP.
 The value contains two fields, as shown.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Radio Type |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 4 for WTP Radio Information
 Length: 2
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Radio Type: The type of radio present. The following values are
 supported
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 1 - 802.11bg: An 802.11bg radio.
 2 - 802.11a: An 802.11a radio.
 3 - 802.16: An 802.16 radio.
 4 - Ultra Wideband: An UWB radio.
 7 - all: Used to specify all radios in the WTP.
5.2. Discovery Response
 The Discovery Response is a mechanism by which an AC advertises its
 services to requesting WTPs.
 Discovery Responses are sent by an AC after receiving a Discovery
 Request.
 When an WTP receives a Discovery Response, it MUST wait for an
 interval not less than DiscoveryInterval for receipt of additional
 Discovery Responses. After the DiscoveryInterval elapses, the WTP
 enters the Joining state and will select one of the ACs that sent a
 Discovery Response and send a Join Request to that AC.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
5.2.1. AC Address
 The AC address message element is used to communicate the identity of
 the AC. The value contains two fields, as shown.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Reserved | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 2 for AC Address
 Length: 7
 Reserved: MUST be set to zero
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 Mac Address: The MAC Address of the AC
5.2.2. AC Descriptor
 The AC payload message element is used by the AC to communicate it's
 current state. The value contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Reserved | Hardware Version ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | HW Ver | Software Version ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | SW Ver | Stations | Limit |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Limit | Radios | Max Radio |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Max Radio | Security |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 6 for AC Descriptor
 Length: 17
 Reserved: MUST be set to zero
 Hardware Version: A 32-bit integer representing the AC's hardware
 version number
 Software Version: A 32-bit integer representing the AC's Firmware
 version number
 Stations: A 16-bit integer representing number of mobile stations
 currently associated with the AC
 Limit: A 16-bit integer representing the maximum number of stations
 supported by the AC
 Radios: A 16-bit integer representing the number of WTPs currently
 attached to the AC
 Max Radio: A 16-bit integer representing the maximum number of WTPs
 supported by the AC
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 Security: A 8 bit bit mask specifying the security schemes
 supported by the AC. The following values are supported (see
 Section 10):
 1 - X.509 Certificate Based
 2 - Pre-Shared Secret
5.2.3. AC Name
 The AC name message element contains an ASCII representation of the
 AC's identity. The value is a variable length byte string. The
 string is NOT zero terminated.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Name ...
 +-+-+-+-+-+-+-+-+
 Type: 31 for AC Name
 Length: > 0
 Name: A variable length ASCII string containing the AC's name
5.2.4. WTP Manager Control IPv4 Address
 The WTP Manager Control IPv4 Address message element is sent by the
 AC to the WTP during the discovery process and is used by the AC to
 provide the interfaces available on the AC, and their current load.
 This message element is useful for the WTP to perform load balancing
 across multiple interfaces.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WTP Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 99 for WTP Manager Control IPv4 Address
 Length: 6
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 IP Address: The IP Address of an interface.
 WTP Count: The number of WTPs currently connected to the interface.
5.2.5. WTP Manager Control IPv6 Address
 The WTP Manager Control IPv6 Address message element is sent by the
 AC to the WTP during the discovery process and is used by the AC to
 provide the interfaces available on the AC, and their current load.
 This message element is useful for the WTP to perform load balancing
 across multiple interfaces.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WTP Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 137 for WTP Manager Control IPv6 Address
 Length: 6
 IP Address: The IP Address of an interface.
 WTP Count: The number of WTPs currently connected to the interface.
5.3. Primary Discovery Request
 The Primary Discovery Request is sent by the WTP in order to
 determine whether its preferred (or primary) AC is available.
 Primary Discovery Request are sent by an WTP when it has a primary AC
 configured, and is connected to another AC. This generally occurs as
 a result of a failover, and is used by the WTP as a means to discover
 when its primary AC becomes available. As a consequence, this
 message is only sent by a WTP when it is in the Run state.
 The frequency of the Primary Discovery Requests should be no more
 often than the sending of the Echo Request message.
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 Upon receiving a discovery request, the AC will respond with a
 Primary Discovery Response sent to the address in the source address
 of the received Primary Discovery Request.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
5.3.1. Discovery Type
 The Discovery Type message element is defined in section
 Section 5.1.1.
5.3.2. WTP Descriptor
 The WTP Descriptor message element is defined in section
 Section 5.1.2.
5.3.3. WTP Radio Information
 An WTP Radio Information message element must be present for every
 radio in the WTP. This message element is defined in section
 Section 5.1.3.
5.4. Primary Discovery Response
 The Primary Discovery Response is a mechanism by which an AC
 advertises its availability and services to requesting WTPs that are
 configured to have the AC as its primary AC.
 Primary Discovery Responses are sent by an AC after receiving a
 Primary Discovery Request.
 When an WTP receives a Primary Discovery Response, it may opt to
 establish an LWAPP connection to its primary AC, based on the
 configuration of the WTP Fallback Status message element on the WTP.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
5.4.1. AC Descriptor
 The Discovery Type message element is defined in section
 Section 5.2.2.
5.4.2. AC Name
 The AC Name message element is defined in section Section 5.2.3.
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5.4.3. WTP Manager Control IPv4 Address
 An WTP Radio Information message element MAY be present for every
 radio in the WTP which are reachable via IPv4. This message element
 is defined in section Section 5.2.4.
5.4.4. WTP Manager Control IPv6 Address
 An WTP Radio Information message element must be present for every
 radio in the WTP which are reachable via IPv6. This message element
 is defined in section Section 5.2.5.
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6. Control Channel Management
 The Control Channel Management messages are used by the WTP and AC to
 create and maintain a channel of communication on which various other
 commands may be transmitted, such as configuration, firmware update,
 etc.
6.1. Join Request
 The Join Request is used by an WTP to inform an AC that it wishes to
 provide services through it.
 Join Requests are sent by an WTP in the Joining state after receiving
 one or more Discovery Responses. The Join Request is also used as an
 MTU discovery mechanism by the WTP. The WTP issues a Join Request
 with a Test message element, bringing the total size of the message
 to exceed MTU.
 If the transport used does not provide MTU path discovery, the
 initial Join Request is padded with the Test message element to 1596
 bytes. If a Join Response is received, the WTP can forward frames
 without requiring any fragmentation. If no Join Response is
 received, it issues a second Join Request padded with the Test
 payload to a total of 1500 bytes. The WTP continues to cycle from
 large (1596) to small (1500) packets until a Join Response has been
 received , or until both packets sizes have been retransmitted 3
 times . If the Join Response is not received after the maximum
 number of retransmissions, the WTP MUST abandon the AC and restart
 the discovery phase.
 When an AC receives a Join Request it will respond with a Join
 Response. If the certificate based security mechanism is used, the
 AC validates the certificate found in the request. If valid, the AC
 generates a session key which will be used to secure the control
 frames it exchanges with the WTP. When the AC issues the Join
 Response, the AC creates a context for the session with the WTP.
 If the pre-shared session key security mechanism is used, the AC
 saves the WTP's nonce, found in the WNonce message element, creates
 its own nonce which it includes in the ANonce message element.
 Finally, the AC creates the PSK-MIC, which is computed using a key
 that is derived from the PSK.
 A Join Request that includes both a WNonce and a Certificate message
 element MUST be considered invalid.
 Details on the key generation is found in Section 10.
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 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.1.1. WTP Descriptor
 The WTP Descriptor message element is defined in section
 Section 5.1.2.
6.1.2. AC Address
 The AC Address message element is defined in section Section 5.2.1.
6.1.3. WTP Name
 The WTP name message element value is a variable length byte string.
 The string is NOT zero terminated.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Name ...
 +-+-+-+-+-+-+-+-+
 Type: 5 for WTP Name
 Length: > 0
 Name: A non zero terminated string containing the WTP's name.
6.1.4. Location Data
 The location data message element is a variable length byte string
 containing user defined location information (e.g. "Next to
 Fridge"). The string is NOT zero terminated.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Location ...
 +-+-+-+-+-+-+-+-+
 Type: 35 for Location Data
 Length: > 0
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 Location: A non zero terminated string containing the WTP's
 location.
6.1.5. WTP Radio Information
 An WTP Radio Information message element must be present for every
 radio in the WTP. This message element is defined in section
 Section 5.1.3.
6.1.6. Certificate
 The certificate message element value is a byte string containing a
 DER-encoded x.509v3 certificate. This message element is only
 included if the LWAPP security type used between the WTP and the AC
 makes use of certificates (see Section 10 for more information).
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Certificate...
 +-+-+-+-+-+-+-+-+
 Type: 44 for Certificate
 Length: > 0
 Certificate: A non zero terminated string containing the device's
 certificate.
6.1.7. Session ID
 The session ID message element value contains a randomly generated
 [4] unsigned 32-bit integer.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Session ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 45 for Session ID
 Length: 4
 Session ID: 32 bit random session identifier.
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6.1.8. Test
 The test message element is used as padding to perform MTU discovery,
 and MAY contain any value, of any length.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Padding ...
 +-+-+-+-+-+-+-+-+
 Type: 18 for Test
 Length: > 0
 Padding: A variable length pad.
6.1.9. XNonce
 The XNonce is used by the WTP to communicate its random nonce during
 the join or rekey phase. See Section 10 for more information.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 111 for XNonce
 Length: 16
 Nonce: 1 16 octet random nonce.
6.2. Join Response
 The Join Response is sent by the AC to indicate to an WTP whether it
 is capable and willing to provide service to it.
 Join Responses are sent by the AC after receiving a Join Request.
 Once the Join Response has been sent, the heartbeat timer is
 initiated for the session to EchoInterval. Expiration of the timer
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 will result in deletion of the AC-WTP session. The timer is
 refreshed upon receipt of the Echo Request.
 If the security method used is certificate based, when a WTP receives
 a Join Response it enters the Joined state and initiates either a
 Configure Request or Image Data to the AC to which it is now joined.
 Upon entering the Joined state, the WTP begins timing an interval
 equal to NeighborDeadInterval. Expiration of the timer will result
 in the transmission of the Echo Request.
 If the security method used is pre-shared secret based, when a WTP
 receives a Join Response that includes a valid PSK-MIC message
 element, it responds with a Join ACK that also MUST include a locally
 computed PSK-MIC message element.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.2.1. Result Code
 The Result Code message element value is a 32-bit integer value,
 indicating the result of the request operation corresponding to the
 sequence number in the message. The Result Code is included in a
 successful Join Response.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Result Code |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 2 for Result Code
 Length: 4
 Result Code: The following values are defined:
 0 Success
 1 Failure (AC List message element MUST be present)
6.2.2. Status
 The Status message element is sent by the AC to the WTP in a non-
 successful Join Response message. This message element is used to
 indicate the reason for the failure and should only be accompanied
 with a Result Code message element that indicates a failure.
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 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Status |
 +-+-+-+-+-+-+-+-+
 Type: 60 for Status
 Length: 1
 Status: The status field indicates the reason for an LWAPP failure.
 The following values are supported:
 1 - Reserved - do not use
 2 - Resource Depletion
 3 - Unknown Source
 4 - Incorrect Data
6.2.3. Certificate
 The Certificate message element is defined in section Section 6.1.6.
 Note this message element is only included if the WTP and the AC make
 use of certificate based security as defined in section Section 10.
6.2.4. WTP Manager Data IPv4 Address
 The WTP Manager Data IPv4 Address message element is optionally sent
 by the AC to the WTP during the join phase. If present, the IP
 Address contained in this message element is the address the WTP is
 to use when sending any of its LWAPP data frames.
 Note this message element is only valid when LWAPP uses the IP/UDP
 layer 3 transport
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 138 for WTP Manager Data IPv4 Address
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 Length: 4
 IP Address: The IP Address of an interface.
6.2.5. WTP Manager Data IPv6 Address
 The WTP Manager Data IPv6 Address message element is optionally sent
 by the AC to the WTP during the join phase. If present, the IP
 Address contained in this message element is the address the WTP is
 to use when sending any of its LWAPP data frames.
 Note this message element is only valid when LWAPP uses the IP/UDP
 layer 3 transport
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 139 for WTP Manager Data IPv6 Address
 Length: 4
 IP Address: The IP Address of an interface.
6.2.6. AC IPv4 List
 The AC List message element is used to configure an WTP with the
 latest list of ACs in a cluster. This message element MUST be
 included if the Join Response returns a failure indicating that the
 AC cannot handle the WTP at this time, allowing the WTP to find an
 alternate AC to connect to.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | AC IP Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 59 for AC List
 Length: >= 4
 AC IP Address: An array of 32-bit integers containing an AC's IPv4
 Address.
6.2.7. AC IPv6 List
 The AC List message element is used to configure an WTP with the
 latest list of ACs in a cluster. This message element MUST be
 included if the Join Response returns a failure indicating that the
 AC cannot handle the WTP at this time, allowing the WTP to find an
 alternate AC to connect to.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | AC IP Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | AC IP Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | AC IP Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | AC IP Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 141 for AC List
 Length: >= 4
 AC IP Address: An array of 32-bit integers containing an AC's IPv6
 Address.
6.2.8. ANonce
 The ANonce message element is sent by a AC during the join or rekey
 phase. The contents of the ANonce are encrypted as described in
 section Section 10 for more information.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 108 for ANonce
 Length: 16
 Nonce: An encrypted 16 octet random nonce.
6.2.9. PSK-MIC
 The PSK-MIC message element includes a message integrity check, whose
 purpose is to provide confirmation to the peer that the sender has
 the proper session key. This message element is only included if the
 security method used between the WTP and the AC is the pre-shared
 secret mechanism. See Section 10 for more information.
 When present, the PSK-MIC message element MUST be the last message
 element in the message. The MIC is computed over the complete LWAPP
 packet, from the LWAPP control header as defined in Section 4.2.1 to
 the end of the packet (which MUST be this PSK-MIC message element).
 The MIC field in this message element and the sequence number field
 in the LWAPP control header MUST be set to zeroes prior to computing
 the MIC. The length field in the LWAPP control header must already
 include this message element prior to computing the MIC.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | SPI | MIC ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 109 for PSK-MIC
 Length: > 1
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 SPI: The SPI field specifies the cryptographic algorithm used to
 create the message integrity check. The following values are
 supported:
 0 - Unused
 1 - HMAC-SHA-1 (RFC 2104 [16])
 MIC: A 20 octet Message Integrity Check.
6.3. Join ACK
 The Join ACK message is sent by the WTP upon receiving a Join
 Response, which has a valid PSK-MIC message element, as a means of
 providing key confirmation to the AC. The Join ACK is only used in
 the case where the WTP makes use of the pre-shared key LWAPP mode
 (See Section 10 for more information).
 Note that the AC should never receive this message unless the
 security method used between the WTP and the AC is pre-shared secret
 based.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.3.1. Session ID
 The Session ID message element is defined in section Section 6.1.7.
6.3.2. WNonce
 The WNonce message element is sent by a WTP during the join or rekey
 phase. The contents of the ANonce are encrypted as described in
 section Section 10 for more information.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Nonce |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 107 for WNonce
 Length: 16
 Nonce: An encrypted 16 octet random nonce.
6.3.3. PSK-MIC
 The PSK-MIC message element is defined in section Section 6.2.9.
6.4. Join Confirm
 The Join Confirm message is sent by the AC upon receiving a Join ACK,
 which has a valid PSK-MIC message element, as a means of providing
 key confirmation to the WTP. The Join Confirm is only used in the
 case where the WTP makes use of the pre-shared key LWAPP mode (See
 Section 10 for more information).
 If the security method used is pre-shared key based, when an WTP
 receives a Join Confirm it enters the Joined state and initiates
 either a Configure Request or Image Data to the AC to which it is now
 joined. Upon entering the Joined state, the WTP begins timing an
 interval equal to NeighborDeadInterval. Expiration of the timer will
 result in the transmission of the Echo Request.
 This message is never received, or sent, when the security type used
 between the WTP and the AC is certificated based.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.4.1. Session ID
 The Session ID message element is defined in section Section 6.1.7.
6.4.2. PSK-MIC
 The PSK-MIC message element is defined in section Section 6.2.9.
6.5. Echo Request
 The Echo Request message is a keepalive mechanism for the LWAPP
 control message.
 Echo Requests are sent periodically by an WTP in the Run state (see
 Figure 2) to determine the state of the connection between the WTP
 and the AC. The Echo Request is sent by the WTP when the Heartbeat
 timer expires, and it MUST start its NeighborDeadInterval timer.
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 The Echo Request carries no message elements.
 When an AC receives an Echo Request it responds with an Echo
 Response.
6.6. Echo Response
 The Echo Response acknowledges the Echo Request, and are only
 accepted while in the Run state (see Figure 2).
 Echo Responses are sent by an AC after receiving an Echo Request.
 After transmitting the Echo Response, the AC should reset its
 Heartbeat timer to expire in the value configured for EchoInterval.
 If another Echo request is not received by the AC when the timer
 expires, the AC SHOULD consider the WTP to no longer be reachable.
 The Echo Response carries no message elements.
 When an WTP receives an Echo Response it stops the
 NeighborDeadInterval timer, and starts the Heartbeat timer to
 EchoInterval.
 If the NeighborDeadInterval timer expires prior to receiving an Echo
 Response, the WTP enters the Idle state.
6.7. Key Update Request
 The Key Update Request is used by the WTP to initiate the rekeying
 phase. This message is sent by a WTP when in the Run state and MUST
 include a new unique Session Identifier. This message MUST also
 include a unique Nonce in the XNonce message element, which is used
 to protect against replay attacks (see Section 10).
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.7.1. Session ID
 The Session ID message element is defined in section Section 6.1.7.
6.7.2. XNonce
 The XNonce message element is defined in section Section 6.1.9.
6.8. Key Update Response
 The Key Update Response is sent by the AC in response to the request
 message, and includes an encrypted ANonce, which is used to derive
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 new session keys. This message MUST include a Session Identifier
 message element, whose value MUST be identical to the one found in
 the Key Update Request.
 The AC MUST include a PSK-MIC message element, which provides message
 integrity over the whole message.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.8.1. Session ID
 The Session ID message element is defined in section Section 6.1.7.
6.8.2. ANonce
 The ANonce message element is defined in section Section 6.2.8.
6.8.3. PSK-MIC
 The PSK-MIC message element is defined in section Section 6.2.9.
6.9. Key Update ACK
 The Key Update ACK is sent by the WTP and includes an encryption
 version of the WTP's Nonce, which is used in the key derivation
 process. The session keys derived are then used as new LWAPP control
 message encryption keys (see Section 10).
 The WTP MUST include a PSK-MIC message element, which provides
 message integrity over the whole message.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.9.1. WNonce
 The WNonce message element is defined in section Section 6.3.2.
6.9.2. PSK-MIC
 The PSK-MIC message element is defined in section Section 6.2.9.
6.10. Key Update Confirm
 The Key Update Confirm closes the rekeying loop, and allows the WTP
 to recognize that the AC has received and processed the key update
 messages. At this point, the WTP updates its session key in its
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 crypto engine, and the associated Initialization Vector, ensuring
 that all future LWAPP control frames are encrypted with the newly
 derived encryption key.
 The WTP MUST include a PSK-MIC message element, which provides
 message integrity over the whole message.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.10.1. PSK-MIC
 The PSK-MIC message element is defined in section Section 6.2.9.
6.11. Key Update Trigger
 The Key Update Trigger is used by the AC to request that a Key Update
 Request be initiated by the WTP.
 Key Update Trigger are sent by an AC in the Run state to inform the
 WTP to initiate a Key Update Request message.
 When a WTP receives a Key Update Trigger it generates a key Update
 Request.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
6.11.1. Session ID
 The Session ID message element is defined in section Section 6.1.7.
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7. WTP Configuration Management
 The Wireless Termination Point Configuration messages are used to
 exchange configuration between the AC and the WTP.
7.1. Configuration Consistency
 The LWAPP protocol provides flexibility in how WTP configuration is
 managed. To put it simply, a WTP has one of two options:
 1. WTP retain no configuration and simply abides by the configuration
 provided by the AC.
 2. WTP retain the configuration of parameters provided by the AC that
 are non-default values.
 If the WTP opts to save configuration locally, the LWAPP protocol
 state machine defines the "configure" state, which is used during the
 initial binding WTP-AC phase, which allows for configuration
 exchange. During this period, the WTP sends its current
 configuration overrides to the AC via the COnfigure Request message.
 A configuration override is a parameter that is non-default. One
 example is that in the LWAPP protocol the default antenna
 configuration is internal omni antenna. However, a WTP that either
 has no internal antennas, or has been explicitely configured by the
 AC to use external antennas, would send its antenna configuration
 during the configure phase, allowing the AC to become aware of the
 WTP's current configuration.
 Once the WTP has provided its configuration to the AC, the AC sends
 down its own configuration. This allows the WTP to inherit the
 configuration and policies on the AC.
 An LWAPP AC maintains a copy of each active WTP's configuration.
 There is no need for versioning or other means to identify
 configuration changes. If a WTP becomes inactive, the AC MAY delete
 the configuration associated with it. If a WTP were to fail, and
 connect to a new AC, it would provide its overriden configuration
 parameters, allowing the new AC to be aware of the WTP's
 configuration.
 As a consequence, this model allows for relisiency, whereby in light
 of an AC failure, another AC could provide service to the WTP. In
 this scenario, the new AC would be automatically updated on any
 possible WTP configuration changes - eliminating the need for
 inter-AC communication or the need for all ACs to be aware of the
 configuration of all WTPs in the network.
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 Once the LWAPP protocol enters the Run state, the WTPs begin to
 provide service. However, it is quite common for administrators to
 require that configuration changes be made while the network is
 operational. Therefore, the Configuration Update Request is sent by
 the AC to the WTP in order to make these changes at run-time.
7.2. Configure Request
 The Configure Request message is sent by an WTP to send its current
 configuration to its AC.
 Configure Requests are sent by an WTP after receiving a Join
 Response, while in the Configure state.
 The Configure Request carries binding specific message elements.
 Refer to the appropriate binding for the definition of this
 structure.
 When an AC receives a Configure Request it will act upon the content
 of the packet and respond to the WTP with a Configure Response.
 The Configure Request includes multiple Administrative State message
 Elements. There is one such message element for the WTP, and then
 one per radio in the WTP.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
7.2.1. Administrative State
 The administrative event message element is used to communicate the
 state of a particular radio. The value contains the following
 fields.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Admin State |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 27 for Administrative State
 Length: 2
 Radio ID: An 8-bit value representing the radio to configure. The
 Radio ID field may also include the value of 0xff, which is used
 to identify the WTP itself. Therefore, if an AC wishes to change
 the administrative state of an WTP, it would include 0xff in the
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 Radio ID field.
 Admin State: An 8-bit value representing the administrative state
 of the radio. The following values are supported:
 1 - Enabled
 2 - Disabled
7.2.2. AC Name
 The AC Name message element is defined in section Section 5.2.3.
7.2.3. AC Name with Index
 The AC Name with Index message element is sent by the AC to the WTP
 to configure preferred ACs. The number of instances where this
 message element would be present is equal to the number of ACs
 configured on the WTP.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Index | AC Name...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 90 for AC Name with Index
 Length: 5
 Index: The index of the preferred server (e.g., 1=primary,
 2=secondary).
 AC Name: A variable length ASCII string containing the AC's name.
7.2.4. WTP Board Data
 The WTP Board Data message element is sent by the WTP to the AC and
 contains information about the hardware present.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Card ID | Card Revision |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WTP Model |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WTP Model |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WTP Serial Number ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Reserved |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Ethernet MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Ethernet MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 50 for WTP Board Data
 Length: 26
 Card ID: A hardware identifier.
 Card Revision: 4 byte Revision of the card.
 WTP Model: 8 byte WTP Model Number.
 WTP Serial Number: 24 byte WTP Serial Number.
 Reserved: A 4 byte reserved field that MUST be set to zero (0).
 Ethernet MAC Address: MAC Address of the WTP's Ethernet interface.
7.2.5. Statistics Timer
 The statistics timer message element value is used by the AC to
 inform the WTP of the frequency which it expects to receive updated
 statistics.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Statistics Timer |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 37 for Statistics Timer
 Length: 2
 Statistics Timer: A 16-bit unsigned integer indicating the time, in
 seconds
7.2.6. WTP Static IP Address Information
 The WTP Static IP Address Information message element is used by an
 AC to configure or clear a previously configured static IP address on
 an WTP.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Netmask |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Gateway |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Static |
 +-+-+-+-+-+-+-+-+
 Type: 82 for WTP Static IP Address Information
 Length: 13
 IP Address: The IP Address to assign to the WTP.
 Netmask: The IP Netmask.
 Gateway: The IP address of the gateway.
 Netmask: The IP Netmask.
 Static: An 8-bit boolean stating whether the WTP should use a
 static IP address or not. A value of zero disables the static IP
 address, while a value of one enables it.
7.2.7. WTP Reboot Statistics
 The WTP Reboot Statistics message element is sent by the WTP to the
 AC to communicate information about reasons why reboots have
 occurred.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Crash Count | LWAPP Initiated Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Link Failure Count | Failure Type |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 67 for WTP Reboot Statistics
 Length: 7
 Crash Count: The number of reboots that have occurred due to an WTP
 crash.
 LWAPP Initiated Count: The number of reboots that have occured at
 the request of some LWAPP message, such as a change in
 configuration that required a reboot or an explicit LWAPP reset
 request.
 Link Failure Count: The number of times that an LWAPP connection
 with an AC has failed.
 Failure Type: The last WTP failure. The following values are
 supported:
 0 - Link Failure
 1 - LWAPP Initiated
 2 - WTP Crash
7.3. Configure Response
 The Configure Response message is sent by an AC and provides an
 opportunity for the AC to override an WTP's requested configuration.
 Configure Responses are sent by an AC after receiving a Configure
 Request.
 The Configure Response carries binding specific message elements.
 Refer to the appropriate binding for the definition of this
 structure.
 When an WTP receives a Configure Response it acts upon the content of
 the packet, as appropriate. If the Configure Response message
 includes a Change State Event message element that causes a change in
 the operational state of one of the Radio, the WTP will transmit a
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 Change State Event to the AC, as an acknowledgement of the change in
 state.
 The following subsections define the message elements that MUST be
 included in this LWAPP operation.
7.3.1. Decryption Error Report Period
 The Decryption Error Report Period message element value is used by
 the AC to inform the WTP how frequently it should send decryption
 error report messages.
 0 1 2
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Report Interval |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 38 for Decryption Error Report Period
 Length: 3
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Report Interval: A 16-bit unsigned integer indicating the time, in
 seconds
7.3.2. Change State Event
 The WTP radios information message element is used to communicate the
 operational state of a radio. The value contains two fields, as
 shown.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | State | Cause |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 26 for Change State Event
 Length: 3
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP.
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 State: An 8-bit boolean value representing the state of the radio.
 A value of one disables the radio, while a value of two enables
 it.
 Cause: In the event of a radio being inoperable, the cause field
 would contain the reason the radio is out of service.
 Cause: In the event of a radio being inoperable, the cause field
 would contain the reason the radio is out of service. The
 following values are supported:
 0 - Normal
 1 - Radio Failure
 2 - Software Failure
7.3.3. LWAPP Timers
 The LWAPP Timers message element is used by an AC to configure LWAPP
 timers on an WTP.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Discovery | Echo Request |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 68 for LWAPP Timers
 Length: 2
 Discovery: The number of seconds between LWAPP Discovery packets,
 when the WTP is in the discovery mode.
 Echo Request: The number of seconds between WTP Echo Request LWAPP
 messages.
7.3.4. AC IPv4 List
 The AC List message element is defined in section Section 6.2.6.
7.3.5. AC IPv6 List
 The AC List message element is defined in section Section 6.2.7.
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7.3.6. WTP Fallback
 The WTP Fallback message element is sent by the AC to the WTP to
 enable or disable automatic LWAPP fallback in the event that an WTP
 detects its preferred AC, and is not currently connected to it.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Mode |
 +-+-+-+-+-+-+-+-+
 Type: 91 for WTP Fallback
 Length: 1
 Mode: The 8-bit boolean value indicates the status of automatic
 LWAPP fallback on the WTP. A value of zero disables the fallback
 feature, while a value of one enables it. When enabled, if the
 WTP detects that its primary AC is available, and it is not
 connected to it, it SHOULD automatically disconnect from its
 current AC and reconnect to its primary. If disabled, the WTP
 will only reconnect to its primary through manual intervention
 (e.g., through the Reset Request command).
7.3.7. Idle Timeout
 The Idle Timeout message element is sent by the AC to the WTP to
 provide it with the idle timeout that it should enforce on its active
 mobile station entries.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Timeout |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 97 for Idle Timeout
 Length: 4
 Timeout: The current idle timeout to be enforced by the WTP.
7.4. Configuration Update Request
 Configure Update Requests are sent by the AC to provision the WTP
 while in the Run state. This is used to modify the configuration of
 the WTP while it is operational.
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 When an AC receives a Configuration Update Request it will respond
 with a Configuration Update Response, with the appropriate Result
 Code.
 The following subsections define the message elements introduced by
 this LWAPP operation.
7.4.1. WTP Name
 The WTP Name message element is defined in section Section 6.1.3.
7.4.2. Change State Event
 The Change State Event message element is defined in section
 Section 7.3.2.
7.4.3. Administrative State
 The Administrative State message element is defined in section
 Section 7.2.1.
7.4.4. Statistics Timer
 The Statistics Timer message element is defined in section
 Section 7.2.5.
7.4.5. Location Data
 The Location Data message element is defined in section
 Section 6.1.4.
7.4.6. Decryption Error Report Period
 The Decryption Error Report Period message element is defined in
 section Section 7.3.1.
7.4.7. AC IPv4 List
 The AC List message element is defined in section Section 6.2.6.
7.4.8. AC IPv6 List
 The AC List message element is defined in section Section 6.2.7.
7.4.9. Add Blacklist Entry
 The Add Blacklist Entry message element is used by an AC to add a
 blacklist entry on an WTP, ensuring that the WTP no longer provides
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 any service to the MAC addresses provided in the message. The MAC
 Addresses provided in this message element are not expected to be
 saved in non-volative memory on the WTP.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Num of Entries| MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 65 for Add Blacklist Entry
 Length: >= 7
 Num of Entries: The number of MAC Addresses in the array.
 MAC Address: An array of MAC Addresses to add to the blacklist
 entry.
7.4.10. Delete Blacklist Entry
 The Delete Blacklist Entry message element is used by an AC to delete
 a previously added blacklist entry on an WTP, ensuring that the WTP
 provides service to the MAC addresses provided in the message.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Num of Entries| MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 66 for Delete Blacklist Entry
 Length: >= 7
 Num of Entries: The number of MAC Addresses in the array.
 MAC Address: An array of MAC Addresses to delete from the blacklist
 entry.
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7.4.11. Add Static Blacklist Entry
 The Add Static Blacklist Entry message element is used by an AC to
 add a permanent blacklist entry on an WTP, ensuring that the WTP no
 longer provides any service to the MAC addresses provided in the
 message. The MAC Addresses provided in this message element are
 expected to be saved in non-volative memory on the WTP.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Num of Entries| MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 70 for Delete Blacklist Entry
 Length: >= 7
 Num of Entries: The number of MAC Addresses in the array.
 MAC Address: An array of MAC Addresses to add to the permanent
 blacklist entry.
7.4.12. Delete Static Blacklist Entry
 The Delete Static Blacklist Entry message element is used by an AC to
 delete a previously added static blacklist entry on an WTP, ensuring
 that the WTP provides service to the MAC addresses provided in the
 message.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Num of Entries| MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 71 for Delete Blacklist Entry
 Length: >= 7
 Num of Entries: The number of MAC Addresses in the array.
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 MAC Address: An array of MAC Addresses to delete from the static
 blacklist entry.
7.4.13. LWAPP Timers
 The LWAPP Timers message element is defined in section Section 7.3.3.
7.4.14. AC Name with Index
 The AC Name with Index message element is defined in section
 Section 7.2.3.
7.4.15. WTP Fallback
 The WTP Fallback message element is defined in section Section 7.3.6.
7.4.16. Idle Timeout
 The Idle Timeout message element is defined in section Section 7.3.7.
7.5. Configuration Update Response
 The Configuration Update Response is the acknowledgement message for
 the Configuration Update Request.
 Configuration Update Responses are sent by an WTP after receiving a
 Configuration Update Request.
 When an AC receives a Configure Update Response the result code
 indicates if the WTP successfully accepted the configuration.
 The following subsections define the message elements that must be
 present in this LWAPP operation.
7.5.1. Result Code
 The Result Code message element is defined in section Section 6.2.1.
7.6. Change State Event Request
 The Change State Event is used by the WTP to inform the AC of a
 change in the operational state.
 The Change State Event message is sent by the WTP when it receives a
 Configuration Response that includes a Change State Event message
 element. It is also sent in the event that the WTP detects an
 operational failure with a radio. The Change State Event may be sent
 in either the Configure or Run state (see Figure 2.
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 When an AC receives a Change State Event it will respond with a
 Change State Event Response and make any necessary modifications to
 internal WTP data structures.
 The following subsections define the message elements that must be
 present in this LWAPP operation.
7.6.1. Change State Event
 The Change State Event message element is defined in section
 Section 7.3.2.
7.7. Change State Event Response
 The Change State Event Response acknowledges the Change State Event.
 Change State Event Response are sent by an WTP after receiving a
 Change State Event.
 The Change State Event Response carries no message elements. Its
 purpose is to acknowledge the receipt of the Change State Event.
 The WTP does not need to perform any special processing of the Change
 State Event Response message.
7.8. Clear Config Indication
 The Clear Config Indication is used to reset an WTP's configuration.
 The Clear Config Indication is sent by an AC to request that an WTP
 reset its configuration to manufacturing defaults. The Clear Config
 Indication message is sent while in the Run LWAPP state.
 The Reset Request carries no message elements.
 When an WTP receives a Clear Config Indication it will reset its
 configuration to manufacturing defaults.
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8. Device Management Operations
 This section defines LWAPP operations responsible for debugging,
 gathering statistics, logging, and firmware management.
8.1. Image Data Request
 The Image Data Request is used to update firmware on the WTP. This
 message and its companion response are used by the AC to ensure that
 the image being run on each WTP is appropriate.
 Image Data Requests are exchanged between the WTP and the AC to
 download a new program image to an WTP.
 When an WTP or AC receives an Image Data Request it will respond with
 a Image Data Response.
 The format of the Image Data and Image Download message elements are
 described in the following subsections.
8.1.1. Image Download
 The image download message element is sent by the WTP to the AC and
 contains the image filename. The value is a variable length byte
 string. The string is NOT zero terminated.
8.1.2. Image Data
 The image data message element is present when sent by the AC and
 contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode | Checksum | Image Data |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Image Data ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 33 for Image Data
 Length: >= 5
 Opcode: An 8-bit value representing the transfer opcode. The
 following values are supported:
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 3 - Image data is included
 5 - An error occurred. Transfer is aborted
 Checksum: A 16-bit value containing a checksum of the image data
 that follows
 Image Data: The Image Data field contains 1024 characters, unless
 the payload being sent is the last one (end of file)
8.2. Image Data Response
 The Image Data Response acknowledges the Image Data Request.
 An Image Data Responses is sent in response to an Image Data Request.
 Its purpose is to acknowledge the receipt of the Image Data Request
 packet.
 The Image Data Response carries no message elements.
 No action is necessary on receipt.
8.3. Reset Request
 The Reset Request is used to cause an WTP to reboot.
 Reset Requests are sent by an AC to cause an WTP to reinitialize its
 operation.
 The Reset Request carries no message elements.
 When an WTP receives a Reset Request it will respond with a Reset
 Response and then reinitialize itself.
8.4. Reset Response
 The Reset Response acknowledges the Reset Request.
 Reset Responses are sent by an WTP after receiving a Reset Request.
 The Reset Response carries no message elements. Its purpose is to
 acknowledge the receipt of the Reset Request.
 When an AC receives a Reset Response it is notified that the WTP will
 now reinitialize its operation.
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8.5. WTP Event Request
 WTP Event Request is used by an WTP to send an information to its AC.
 These types of events may be periodical, or some asynchronous event
 on the WTP. For instance, an WTP collects statistics and uses the
 WTP Event Request to transmit this information to the AC.
 When an AC receives a WTP Event Request it will respond with a WTP
 Event Request.
 The WTP Event Request message MUST contain one of the following
 message element described in the next subsections, or a message
 element that is defined for a specific technology.
8.5.1. Decryption Error Report
 The Decryption Error Report message element value is used by the WTP
 to inform the AC of decryption errors that have occured since the
 last report.
 0 1 2
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID |Num Of Entries | Mobile MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Mobile MAC Address[] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 39 for Decryption Error Report
 Length: >= 8
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Num Of Entries: An 8-bit unsigned integer indicating the number of
 mobile MAC addresses.
 Mobile MAC Address: An array of mobile station MAC addresses that
 have caused decryption errors.
8.5.2. Duplicate IPv4 Address
 The Duplicate IPv4 Address message element is used by an WTP to
 inform an AC that it has detected another host using the same IP
 address it is currently using.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 77 for Duplicate IPv4 Address
 Length: 10
 IP Address: The IP Address currently used by the WTP.
 MAC Address: The MAC Address of the offending device.
8.5.3. Duplicate IPv6 Address
 The Duplicate IPv6 Address message element is used by an WTP to
 inform an AC that it has detected another host using the same IP
 address it is currently using.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IP Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 77 for Duplicate IPv6 Address
 Length: 10
 IP Address: The IP Address currently used by the WTP.
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 MAC Address: The MAC Address of the offending device.
8.6. WTP Event Response
 WTP Event Response acknowledges the WTP Event Request.
 WTP Event Response are sent by an AC after receiving a WTP Event
 Request.
 The WTP Event Response carries no message elements.
8.7. Data Transfer Request
 The Data Transfer Request is used to upload debug information from
 the WTP to the AC.
 Data Transfer Requests are sent by the WTP to the AC when it
 determines that it has important information to send to the AC. For
 instance, if the WTP detects that its previous reboot was caused by a
 system crash, it would want to send the crash file to the AC. The
 remote debugger function in the WTP also uses the data transfer
 request in order to send console output to the AC for debugging
 purposes.
 When an AC receives an Data Transfer Request it will respond with a
 Data Transfer Response. The AC may log the information received, as
 it sees fit.
 The data transfer request message MUST contain ONE of the following
 message element described in the next subsection.
8.7.1. Data Transfer Mode
 The Data Transfer Mode message element is used by the AC to request
 information from the WTP for debugging purposes.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Data Type |
 +-+-+-+-+-+-+-+-+
 Type: 52 for Data Transfer Mode
 Length: 1
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 Data Type: An 8-bit value the type of information being requested.
 The following values are supported:
 1 - WTP Crash Data
 2 - WTP Memory Dump
8.7.2. Data Transfer Data
 The Data Transfer Data message element is used by the WTP to provide
 information to the AC for debugging purposes.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Data Type | Data Length | Data ....
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 53 for Data Transfer Data
 Length: >= 3
 Data Type: An 8-bit value the type of information being sent. The
 following values are supported:
 1 - WTP Crash Data
 2 - WTP Memory Dump
 Data Length: Length of data field.
 Data: Debug information.
8.8. Data Transfer Response
 The Data Transfer Response acknowledges the Data Transfer Request.
 An Data Transfer Response is sent in response to an Data Transfer
 Request. Its purpose is to acknowledge the receipt of the Data
 Transfer Request packet.
 The Data Transfer Response carries no message elements.
 Upon receipt of a Data Transfer Response, the WTP transmits more
 information, if any is available.
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9. Mobile Session Management
 Messages in this section are used by the AC to create, modify or
 delete mobile station session state on the WTPs.
9.1. Mobile Config Request
 The Mobile Config Request message is used to create, modify or delete
 mobile session state on an WTP. The message is sent by the AC to the
 WTP, and may contain one or more message elements. The message
 elements for this LWAPP control message include information that is
 generally highly technology specific. Therefore, please refer to the
 appropriate binding section or document for the definitions of the
 messages elements that may be used in this control message.
 This section defines the format of the Delete Mobile message element,
 since it does not contain any technology specific information.
9.1.1. Delete Mobile
 The Delete Mobile message element is used by the AC to inform an WTP
 that it should no longer provide service to a particular mobile
 station. The WTP must terminate service immediately upon receiving
 this message element.
 The transmission of a Delete Mobile message element could occur for
 various reasons, including for administrative reaons, as a result of
 the fact that the mobile has roamed to another WTP, etc.
 Once access has been terminated for a given station, any future
 packets received from the mobile must result in a deauthenticate
 message, as specified in [6].
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 30 for Delete Mobile
 Length: 7
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 Radio ID: An 8-bit value representing the radio
 MAC Address: The mobile station's MAC Address
9.2. Mobile Config Response
 The Mobile Configuration Response is used to acknowledge a previously
 received Mobile Configuration Request, and includes a Result Code
 message element which indicates whether an error occured on the WTP.
 This message requires no special processing, and is only used to
 acknowledge the Mobile Configuration Request.
 The data transfer request message MUST contain the message elements
 described in the next subsection.
9.2.1. Result Code
 The Result Code message element is defined in section Section 6.2.1.
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10. LWAPP Security
 Note: This version only defines a certificate and a shared secret
 based mechanism to secure control LWAPP traffic exchanged between the
 WTP and the AC.
10.1. Securing WTP-AC communications
 While it is generally straightforward to produce network
 installations in which the communications medium between the WTP and
 AC is not accessible to the casual user (e.g. these LAN segments are
 isolated, no RJ45 or other access ports exist between the WTP and the
 AC), this will not always be the case. Furthermore, a determined
 attacker may resort to various more sophisticated monitoring and/or
 access techniques, thereby compromising the integrity of this
 connection.
 In general, a certain level of threat on the local (wired) LAN is
 expected and accepted in most computing environments. That is, it is
 expected that in order to provide users with an acceptable level of
 service and maintain reasonable productivity levels, a certain amount
 of risk must be tolerated. It is generally believed that a certain
 perimeter is maintained around such LANs, that an attacker must have
 access to the building(s) in which such LANs exist, and that they
 must be able to "plug in" to the LAN in order to access the network.
 With these things in mind, we can begin to assess the general
 security requirements for AC-WTP communications. While an in-depth
 security analysis of threats and risks to these communication is
 beyond the scope of this document, some discussion of the motivation
 for various security-related design choices is useful. The
 assumptions driving the security design thus far include the
 following:
 o WTP-AC communications take place over a wired connection which may
 be accessible to a sophisticated attacker
 o access to this connection is not trivial for an outsider (i.e.
 someone who does not "belong" in the building) to access
 o if authentication and/or privacy of end to end traffic for which
 the WTP and AC are intermediaries is required, this may be
 provided via IPsec [15].
 o privacy and authentication for at least some WTP-AC control
 traffic is required (e.g. WEP keys for user sessions, passed from
 AC to WTP)
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 o the AC can be trusted to generate strong cryptographic keys
 AC-WTP traffic can be considered to consist of two types: data
 traffic (e.g. to or from an end user), and control traffic which is
 strictly between the AC and WTP. Since data traffic may be secured
 using IPsec (or some other end-to-end security mechanism), we confine
 our solution to control traffic. The resulting security consists of
 two components: an authenticated key exchange, and control traffic
 security encapsulation. The security encapsulation is accomplished
 using AES CCM, described in [3]. This encapsulation provides for
 strong AES-based authentication and encryption. The exchange of
 cryptographic keys used for CCM is described below.
10.2. LWAPP Frame Encryption
 While, the LWAPP protocol uses AES-CCM to encrypt control traffic, it
 is important to note that not all control frames are encrypted. The
 LWAPP discovery and join phase are not encrypted. The Discovery
 messages are sent in the clear since there does not exist a security
 association between the WTP and the AC during the discovery phase.
 The Join phase is an authenticated exchange used to negotiate
 symmetric session keys (see Section 10.3).
 Once the join phase has been successfully completed, the LWAPP state
 machine Figure 2 will move to the Configure state, at which time all
 LWAPP control frames are encrypted using AES-CCM.
 Encryption of a control message begins at the Message Element field,
 meaning the Msg Type, Seq Num, Msg Element Length and Session ID
 fields are left intact (see Section 4.2.1).
 The AES-CCM 12 byte authentication data is appended to the end of the
 message. The authentication data is calculated from the start of the
 LWAPP packet, and includes the complete LWAPP control header (see
 Section 4.2.1).
 The AES-CCM block cipher protocol requires an initialization vector.
 The LWAPP protocol requires that the WTP and the AC maintain two
 separate IVs, one for transmission and one for reception. The IV
 derived during the key exchange phase by both the WTP and the AC is
 used as the base for all encrypted packets with a new key.
10.3. Authenticated Key Exchange
 This section describes the key management component of the LWAPP
 protocol. There are two modes supported by LWAPP; certificate and
 pre-shared key.
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10.3.1. Terminology
 This section details the key management protocol which makes use of
 pre-shared secrets.
 The following notations are used throughout this section:
 o PSK - the pre-shared key shared between the WTP and the AC
 o Kpriv - the private key of a public-private key pair
 o Kpub - the public key of the pair
 o SessionID - randomly generated LWAPP session identifier, provided
 by the WTP in the Join Request
 o E-x{Kpub, M} - RSA encryption of M using X's public key
 o D-x{Kpriv, C} - RSA decryption of C using X's private key
 o AES-CMAC(key, packet) - A message integrity check, using AES-CMAC
 and key, of the complete LWAPP packet, with the sequence number
 field and the payload of the PSK-MIC message element set to zero.
 o AES-E(key, plaintext) - Plaintext is encrypted with key, using
 AES.
 o AES-D(key, ciphertext) - ciphertext is decrypted with key, using
 AES.
 o Certificate-AC - AC's Certificate
 o Certificate-WTP - WTP's Certificate
 o WTP-MAC - The WTP's MAC Address.
 o AC-MAC - The AC's MAC Address.
 o RK0 - the root key, which is created through a KDF function.
 o RK0E - the root Encryption key, derived from RK0.
 o RK0M - the root MIC key, derived from RK0.
 o SK1 - the session Key
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 o SK1C - the session confirmation Key, derived from SK
 o SK1E - the session encryption Key, derived from SK
 o SK1W - the session keywrap Key, derived from SK (see RFC 3394 [9])
 o WNonce - The WTP's randomly generated Nonce.
 o ANonce - The AC's randomly generated Nonce.
 o EWNonce - The payload of the WNonce message element, which
 includes the WNonce.
 o EANonce - The payload of the ANonce message element, which
 includes the ANonce.
10.3.2. Initial Key Generation
 The AC and WTP accomplish mutual authentication and a cryptographic
 key exchange in a dual round trip using the Join Request, Join
 Response, Join ACK and Join Confirm (see Section 6.1).
 The following text describes the exchange between the WTP and the AC
 that creates a session key, which is used to secure LWAPP control
 messages.
 o The WTP creates a Join Request using the following process:
 o If Certificate based security is used, the WTP adds the
 Certificate message element (see Section 6.1.6) with its
 contents set to Certificate-WTP.
 o Adds the Session ID message element (see Section 6.1.7) with
 the contents set to a randomly generated session identifer (see
 RFC 1750 [4]). The WTP MUST save the Session ID in order to
 validate the Join Response.
 o Creates a random Nonce, included in the XNonce message element
 (see Section 6.1.9). The WTP MUST save the XNonce to validate
 the Join Response.
 o The WTP transmits the Join Request to the AC.
 o Upon receiving the Join Request the AC uses the following process:
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 o The AC creates the Join Response, and ensures that the Session
 ID message element matches the value found in the Join Request.
 o If Certificate based security is used, the AC:
 o Adds the Certificate-AC to the Certificate message element.
 o Creates a random 'AC Nonce' and encrypts it using the
 following algorithm E-wtp(Kpub, XNonce XOR 'AC Nonce'). The
 encrypted contents are added to the ANonce's message element
 payload.
 o If pre-shared key based security is used, the AC:
 o Creates RK0 through the following algorithm: RK0 = KDF-
 256{PSK, "LWAPP PSK Top K0" || Session ID || WTP-MAC || AC-
 MAC}, where WTP-MAC is the WTP's MAC Address in the form
 "xx:xx:xx:xx:xx:xx". Similarly, the AC-MAC is an ASCII
 encoding of the AC's MAC Address, of the form "xx:xx:xx:xx:
 xx:xx". The resulting K0 is split into the following:
 o The first 16 octets is known as RK0E, and is used as an
 encryption key
 o The second 16 octets is known as RK0M, and is used for
 MIC'ing purposes
 o Creates a random 'AC Nonce' and encrypts it using the
 following algorithm AES-E(RK0E, XNonce XOR 'AC Nonce'). The
 encrypted contents are added to the ANonce's message element
 payload.
 o The AC adds a MIC to the contents of the Join Response using
 AES-CMAC(RK0M, Join Response) and adds the resulting hash to
 the PSK-MIC (Section 6.2.9) message element.
 o Upon receiving the Join Response the WTP uses the following
 process:
 o If Pre-shared key is used, the WTP authenticates the Join
 Response's PSK-MIC message element. If authentication fails,
 the packet is dropped.
 o The WTP decrypts the ANonce message element and XOR's the value
 with XNonce to retrieve the 'AC Nonce'. The ANonce payload is
 referred to as ciphertext below:
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 o If Pre-shared key is used, use AES-D(RK0E, ciphertext). The
 'AC Nonce' is then recovered using XNonce XOR plaintext.
 o If certificates are used, use d-wtp(Kpriv, ciphertext). The
 'AC Nonce' is then recovered using XNonce XOR plaintext.
 o The WTP creates a random 'WTP Nonce'.
 o The WTP uses the KDF function to create a 64 octet session key
 (SK). The KDF function used is as follows: KDF-512{'WTP Nonce'
 || 'AC Nonce', "LWAPP Key Generation", WTP-MAC || AC-MAC}. The
 KDF function is defined in [7].
 o SK is then broken down into three separate session keys with
 different purposes:
 o The first 16 octets is known as SK1C, and is used as a
 confirmation key
 o The second 16 octets is known as SK1E, and is as the
 encryption key
 o The third 16 octets is known as SK1D, and is used as the
 keywrap key
 o The fourth 16 octets is known as IV, and is used as the
 Initialization Vector during encryption
 o The WTP creates the Join ACK message.
 o If Certificate based security is used, the AC:
 o Encrypt the 'WTP Nonce' using following algorithm E-ac(Kpub,
 'WTP Nonce'). The encrypted contents are added to the
 WNonce's message element payload.
 o If pre-shared key based security is used, the AC:
 o Encrypt the 'WTP Nonce' using following algorithm AES-
 E(RK0E, 'WTP Nonce'). The encrypted contents are added to
 the WNonce's message element payload.
 o The WTP adds a MIC to the contents of the Join ACK using AES-
 CMAC(SK1M, Join ACK) and adds the resulting hash to the PSK-MIC
 (Section 6.2.9) message element.
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 o The WTP then transmits the Join ACK to the AC.
 o Upon receiving the Join ACK the AC uses the following process:
 o The AC authenticates the Join ACK through the PSK-MIC message
 element. If authentic, the AC decrypts the WNonce message
 element to retrieve the 'WTP Nonce'. If the Join ACK could not
 be authenticated, the packet is dropped.
 o The AC decrypts the WNonce message element to retrieve the 'WTP
 Nonce'. The WNonce payload is referred to as ciphertext below:
 o If Pre-shared key is used, use AES-D(RK0E, ciphertext). The
 plaintext is then considered the 'WTP Nonce'.
 o If certificates are used, use d-ac(Kpriv, ciphertext). The
 plaintext is then considered the 'WTP Nonce'.
 o The AC then uses the KDF function to create a 64 octet session
 key (SK). The KDF function used is as follows: KDF-512{'WTP
 Nonce' || 'AC Nonce', "LWAPP Key Generation", WTP-MAC || AC-
 MAC}. The KDF function is defined in [7]. The SK is split
 into SK1C, SK1E, SK1D and IV as previously noted.
 o The AC creates the Join Confirm.
 o The AC adds a MIC to the contents of the Join Confirm using
 AES-CMAC(SK1M, Join Confirm) and adds the resulting hash to the
 MIC (Section 6.2.9) message element.
 o The AC then transmits the Join Confirm to the WTP.
 o Upon receiving the Join Confirm the WTP uses the following
 process:
 o The WTP authenticates the Join Confirm through the PSK-MIC
 message element. If the Join Confirm could not be
 authenticated, the packet is dropped.
 o SK1E is now plumbed into the AC and WTP's crypto engine as the
 AES-CCM LWAPP control encryption session key. Furthermore, the
 random IV is used as the base Initialization Vector. From this
 point on, all control protocol payloads between the WTP and AC are
 encrypted and authenticated using the new session key.
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10.3.3. Refreshing Cryptographic Keys
 Since AC-WTP associations will tend to be relatively long-lived, it
 is sensible to periodically refresh the encryption and authentication
 keys; this is referred to as "rekeying". When the key lifetime
 reaches 95% of the configured value, identified in the KeyLifetime
 timer (see Section 12), the rekeying will proceed as follows:
 o The WTP creates RK0 through the previously defined KDF algorithm:
 RK0 = KDF-256{SK1D, "LWAPP PSK Top K0" || Session ID || WTP-MAC ||
 AC-MAC}. Note the difference in this specific instance is that
 SK1D that was previously generated is used instead of the PSK.
 Note this is used in both the certificate and pre-shared key
 modes. The resulting RK0 create RK0E, RK0M.
 o The remaining steps used are identical as the join process, with
 the exception that the rekey messages are used instead of join
 messages, and the fact that the messages are encrypted using the
 previously created SK1E. This means the Join Request is replaced
 with the Rekey Request, the Join Response is replaced with the
 Rekey Response, etc. The two differences between the rekey and
 the join process are:
 o The Certificate-WTP and Certificate-AC are not included in the
 Rekey-Request and Rekey-Response, respectively.
 o Regardless of whether certificates or pre-shared key was used
 in the initial key derivation, the process now uses the pre-
 shared key mode only, using SK1D as the "PSK".
 o The Key Update Request is sent to the AC.
 o The newly created SK1E is now plumbed into the AC and WTP's crypto
 engine as the AES-CCM LWAPP control encryption session key.
 Furthermore, the new random IV is used as the base Initialization
 Vector. From this point on, all control protocol payloads between
 the WTP and AC are encrypted and authenticated using the new
 session key.
 If either the WTP or the AC do not receive an expected response by
 the time the ResponseTimeout timer expires (see Section 12), the
 WTP MUST delete the new and old session information, and reset the
 state machine to the Idle state.
 Following a rekey process, both the WTP and the AC keep the
 previous encryption for 5-10 seconds in order to be able to
 process packets that arrive out of order.
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10.4. Certificate Usage
 Validation of the certificates by the AC and WTP is required so that
 only an AC may perform the functions of an AC and that only a WTP may
 perform the functions of a WTP. This restriction of functions to the
 AC or WTP requires that the certificates used by the AC MUST be
 distinguishable from the certificate used by the WTP. To accomplish
 this differentiation, the x.509v3 certificates MUST include the
 Extensions field [10] and MUST include the NetscapeComment [11]
 extension.
 For an AC, the value of the NetscapeComment extension MUST be the
 string "CAPWAP AC Device Certificate". For a WTP, the value of the
 NetscapeComment extension MUST be the string "CAPWAP WTP Device
 Certificate".
 Part of the LWAPP certificate validation process includes ensuring
 that the proper string is included in the NetscapeComment extension,
 and only allowing the LWAPP session to be established if the
 extension does not represent the same role as the device validating
 the certificate. For instance, a WTP MUST NOT accept a certificate
 whose NetscapeComment field is set to "CAPWAP WTP Device
 Certificate".
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11. IEEE 802.11 Binding
 This section defines the extensions required for the LWAPP protocol
 to be used with the IEEE 802.11 protocol.
11.1. Division of labor
 The LWAPP protocol, when used with IEEE 802.11 devices, requires a
 specific behavior from the WTP and the AC, specifically in terms of
 which 802.11 protocol functions are handled.
 For both the Split and Local MAC approaches, the CAPWAP functions, as
 defined in the taxonomy specification, reside in the AC.
11.1.1. Split MAC
 This section shows the division of labor between the WTP and the AC
 in a Split MAC architecture. Figure 3 shows the clear separation of
 functionality among LWAPP components.
 Function Location
 Distribution Service AC
 Integration Service AC
 Beacon Generation WTP
 Probe Response WTP
 Power Mgmt/Packet Buffering WTP
 Fragmentation/Defragmentation WTP
 Assoc/Disassoc/Reassoc AC
 802.11e
 Classifying AC
 Scheduling WTP/AC
 Queuing WTP
 802.11i
 802.1X/EAP AC
 Key Management AC
 802.11 Encryption/Decryption WTP or AC
 Figure 3: Mapping of 802.11 Functions for Split MAC Architecture
 The Distribution and Integration services reside on the AC, and
 therefore all user data is tunneled between the WTP and the AC. As
 noted above, all real-time 802.11 services, including the control
 protocol and the beacon and probe response frames, are handled on the
 WTP.
 All remaining 802.11 MAC management frames are supported on the AC,
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 including the Association Request which allows the AC to be involved
 in the access policy enforcement portion of the 802.11 protocol. The
 802.1X and 802.11i key management function are also located on the
 AC.
 While the admission control component of 802.11e resides on the AC,
 the real time scheduling and queuing functions are on the WTP. Note
 this does not exclude the AC from providing additional policing and
 scheduling functionality.
 Note that in the following figure, the use of '( - )' indicates that
 processing of the frames is done on the WTP.
 Client WTP AC
 Beacon
 <-----------------------------
 Probe Request
 ----------------------------( - )------------------------->
 Probe Response
 <-----------------------------
 802.11 AUTH/Association
 <--------------------------------------------------------->
 Add Mobile (Clear Text, 802.1X Only)
 <------------------------->
 802.1X Authentication & 802.11i Key Exchange
 <--------------------------------------------------------->
 Add Mobile (AES-CCMP, PTK=x)
 <------------------------->
 802.11 Action Frames
 <--------------------------------------------------------->
 802.11 DATA (1)
 <---------------------------( - )------------------------->
 Figure 4: Split MAC Message Flow
 Figure 4 provides an illustration of the division of labor in a Split
 MAC architecture. In this example, a WLAN has been created that is
 configured for 802.11i, using AES-CCMP for privacy. The following
 process occurs:
 o The WTP generates the 802.11 beacon frames, using information
 provided to it through the Add WLAN (see Section Section 11.8.1.1)
 message element.
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 o The WTP processes the probe request and responds with a
 corresponding probe response. The problem request is then
 forwarded to the AC for optional processing.
 o The WTP forwards the 802.11 Authentication and Association frames
 to the AC, which is responsible for responding to the client.
 o Once the association is complete, the AC transmits an LWAPP Add
 Mobile request to the WTP (see section Section 11.7.1.1. In the
 above example, the WLAN is configured for 802.1X, and therefore
 the '802.1X only' policy bit is enabled.
 o If the WTP is providing encryption/decryption services, once the
 client has completed the 802.11i key exchange, the AC transmits
 another Add Mobile request to the WTP, stating the security policy
 to enforce for the client (in this case AES-CCMP), as well as the
 encryption key to use. If encryption/decryption is handled in the
 AC, the Add Mobile request would have the encryption policy set to
 "Clear Text".
 o The WTP forwards any 802.11 Action frames received to the AC.
 o All client data frames are tunneled between the WTP and the AC.
 Note that the WTP is responsible for encrypting and decrypting
 frames, if it was indicated in the Add Mobile request.
11.1.2. Local MAC
 This section shows the division of labor between the WTP and the AC
 in a Local MAC architecture. Figure 5 shows the clear separation of
 functiionality among LWAPP components.
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 Function Location
 Distribution Service WTP
 Integration Service WTP
 Beacon Generation WTP
 Probe Response WTP
 Power Mgmt/Packet Buffering WTP
 Fragmentation/Defragmentation WTP
 Assoc/Disassoc/Reassoc WTP
 802.11e
 Classifying WTP
 Scheduling WTP
 Queuing WTP
 802.11i
 802.1X/EAP AC
 Key Management AC
 802.11 Encryption/Decryption WTP
 Figure 5: Mapping of 802.11 Functions for Local AP Architecture
 Given the Distribution and Integration Services exist on the WTP,
 client data frames are not forwarded to the AC, with the exception
 listed in the following paragraphs.
 While the MAC is terminated on the WTP, it is necessary for the AC to
 be aware of mobility events within the WTPs. As a consequence, the
 WTP MUST forward the 802.11 Association Requests to the AC, and the
 AC MAY reply with a failed Association Response if it deems it
 necessary.
 The 802.1X and 802.11i Key Management function resides in the AC.
 Therefore, the WTP MUST forward all 802.1X/Key Management frames to
 the AC and forward the associated responses to the station.
 Note that in the following figure, the use of '( - )' indicates that
 processing of the frames is done on the WTP.
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 Client WTP AC
 Beacon
 <-----------------------------
 Probe
 <---------------------------->
 802.11 AUTH
 <-----------------------------
 802.11 Association
 <---------------------------( - )------------------------->
 Add Mobile (Clear Text, 802.1X Only)
 <------------------------->
 802.1X Authentication & 802.11i Key Exchange
 <--------------------------------------------------------->
 802.11 Action Frames
 <--------------------------------------------------------->
 Add Mobile (AES-CCMP, PTK=x)
 <------------------------->
 802.11 DATA
 <----------------------------->
 Figure 6: Local MAC Message Flow
 Figure 6 provides an illustration of the division of labor in a Local
 MAC architecture. In this example, a WLAN has been created that is
 configured for 802.11i, using AES-CCMP for privacy. The following
 process occurs:
 o The WTP generates the 802.11 beacon frames, using information
 provided to it through the Add WLAN (see Section Section 11.8.1.1)
 message element.
 o The WTP processes the probe request and responds with a
 corresponding probe response.
 o The WTP forwards the 802.11 Authentication and Association frames
 to the AC, which is responsible for responding to the client.
 o Once the association is complete, the AC transmits an LWAPP Add
 Mobile request to the WTP (see section Section 11.7.1.1. In the
 above example, the WLAN is configured for 802.1X, and therefore
 the '802.1X only' policy bit is enabled.
 o The WTP forwards all 802.1X and 802.11i key exchange messages to
 the AC for processing.
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 o The AC transmits another Add Mobile request to the WTP, stating
 the security policy to enforce for the client (in this case AES-
 CCMP), as well as the encryption key to use. The Add Mobile
 request MAY include a VLAN name, which when present is used by the
 WTP to identify the VLAN on which the user's data frames are to be
 bridged.
 o The WTP forwards any 802.11 Action frames received to the AC.
 o The WTP locally bridges all client data frames, and provides the
 necessary encryption and decryption services.
11.2. Roaming Behavior and 802.11 security
 It is important that LWAPP implementations react properly to mobile
 devices associating to the networks in how they generate Add Mobile
 and Delete Mobile messages. This section expands upon the examples
 provided in the previous section, and describes how the LWAPP control
 protocol is used in order to provide secure roaming.
 Once a client has successfully associated with the network in a
 secure fashion, it is likely to attempt to roam to another access
 point. Figure 7 shows an example of a currently associated station
 moving from its "Old WTP" to a new WTP. The figure is useful for
 multiple different security policies, including standard 802.1X and
 dynamic WEP keys, WPA or even WPA2 both with key caching (where the
 802.1x exchange would be bypassed) and without.
 Client Old WTP WTP AC
 Association Request/Response
 <--------------------------------------( - )-------------->
 Add Mobile (Clear Text, 802.1X Only)
 <---------------->
 802.1X Authentication (if no key cache entry exists)
 <--------------------------------------( - )-------------->
 802.11i 4-way Key Exchange
 <--------------------------------------( - )-------------->
 Delete Mobile
 <---------------------------------->
 Add Mobile (AES-CCMP, PTK=x)
 <---------------->
 Figure 7: Client Roaming Example
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11.3. Transport specific bindings
 All LWAPP transports have the following IEEE 802.11 specific
 bindings:
11.3.1. Status and WLANS field
 The interpretation of this 16 bit field depends on the direction of
 transmission of the packet. Refer to the figure in Section
 Section 3.1.
 Status
 When an LWAPP packet is transmitted from an WTP to an AC, this field
 is called the status field and indicates radio resource information
 associated with the frame. When the message is an LWAPP control
 message this field is transmitted as zero.
 The status field is divided into the signal strength and signal to
 noise ratio with which an IEEE 802.11 frame was received, encoded in
 the following manner:
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | RSSI | SNR |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 RSSI: RSSI is a signed, 8-bit value. It is the received signal
 strength indication, in dBm.
 SNR: SNR is a signed, 8-bit value. It is the signal to noise ratio
 of the received IEEE 802.11 frame, in dB.
 WLANs field: When an LWAPP data message is transmitted from an AC
 to an WTP, this 16 bit field indicates on which WLANs the
 encapsulated IEEE 802.11 frame is to be transmitted. For unicast
 packets, this field is not used by the WTP. For broadcast or
 multicast packets, the WTP might require this information if it
 provides encryption services.
 Given that a single broadcast or multicast packet might need to be
 sent to multiple wireless LANs (presumably each with a different
 broadcast key), this field is defined as a bit field. A bit set
 indicates a WLAN ID (see Section Section 11.8.1.1) which will be
 sent the data. The WLANS field is encoded in the following
 manner:
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 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WLAN ID(s) |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
11.4. BSSID to WLAN ID Mapping
 The LWAPP protocol makes assumptions regarding the BSSIDs used on the
 WTP. It is a requirement for the WTP to use a contiguous block of
 BSSIDs. The WLAN Identifier field, which is managed by the AC, is
 used as an offset into the BSSID list.
 For instance, if a WTP had a base BSSID address of 00:01:02:00:00:00,
 and the AC sent an Add WLAN message with a WLAN Identifier of 2 (see
 Section Section 11.8.1.1), the BSSID for the specific WLAN on the WTP
 would be 00:01:02:00:00:02.
 The WTP communicates the maximum number of BSSIDs that it supports
 during the Config Request within the IEEE 802.11 WTP WLAN Radio
 Configuration message element (see Section 11.9.1).
11.5. Quality of Service
 It is recommended that 802.11 MAC management be sent by both the AC
 and the WTP with appropriate Quality of Service values, ensuring that
 congestion in the network minimizes occurences of packet loss.
 Therefore, a Quality of Service enabled LWAPP device should use:
 802.1P: The precedence value of 6 SHOULD be used for all 802.11 MAC
 management messages, except for Probe Requests which SHOULD use 4.
 DSCP: The dscp tag value of 46 SHOULD be used for all 802.11 MAC
 management messages, except for Probe Requests which SHOULD use
 34.
11.6. Data Message bindings
 There are no LWAPP Data Message bindings for IEEE 802.11.
11.7. Control Message bindings
 The IEEE 802.11 binding has the following Control Message
 definitions.
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11.7.1. Mobile Config Request
 This section contains the 802.11 specific message elements that are
 used with the Mobile Config Request.
11.7.1.1. Add Mobile
 The Add Mobile Request is used by the AC to inform an WTP that it
 should forward traffic from a particular mobile station. The add
 mobile request may also include security parameters that must be
 enforced by the WTP for the particular mobile.
 When the AC sends an Add Mobile Request, it includes any security
 parameters that may be required. An AC that wishes to update a
 mobile's policy on an WTP may be done by simply sending a new Add
 Mobile message element.
 When an WTP receives an Add Mobile message element, it must first
 override any existing state it may have for the mobile station in
 question. The latest Add Mobile overrides any previously received
 messages. If the Add Mobile message element's EAP Only bit is set,
 the WTP MUST drop all 802.11 packets that do not contain EAP packets.
 Note that when EAP Only is set, the Encryption Policy field MAY have
 additional values, and therefore it is possible to inform an WTP to
 only accept encrypted EAP packets. Once the mobile station has
 successfully completed EAP authentication, the AC must send a new Add
 Mobile message element to push the session key down to the WTP as
 well as to remove the EAP Only restriction.
 If the QoS field is set, the WTP MUST observe and provide policing of
 the 802.11e priority tag to ensure that it does not exceed the value
 provided by the AC.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Association ID | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |E|C| Encryption Policy |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Encrypt Policy | Session Key... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Pairwise TSC... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Pairwise RSC... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Capabilities | WLAN ID | WME Mode |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 802.11e Mode | Qos | Supported Rates |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Supported Rates |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | VLAN Name...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 29 for Add Mobile
 Length: 36
 Radio ID: An 8-bit value representing the radio
 Association ID: A 16-bit value specifying the 802.11 Association
 Identifier
 MAC Address: The mobile station's MAC Address
 E: The one bit field is set by the AC to inform the WTP that is
 MUST NOT accept any 802.11 data frames, other than 802.1X frames.
 This is the equivalent of the WTP's 802.1X port for the mobile
 station to be in the closed state. When set, the WTP MUST drop
 any non-802.1X packets it receives from the mobile station.
 C: The one bit field is set by the AC to inform the WTP that
 encryption services will be provided by the AC. When set, the WTP
 SHOULD police frames received from stations to ensure that they
 comply to the stated encryption policy, but does not need to take
 specific cryptographic action on the frame. Similarly, for
 transmitted frames, the WTP only needs to forward already
 encrypted frames.
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 Encryption Policy: The policy field informs the WTP how to handle
 packets from/to the mobile station. The following values are
 supported:
 0 - Encrypt WEP 104: All packets to/from the mobile station must
 be encrypted using standard 104 bit WEP.
 1 - Clear Text: All packets to/from the mobile station do not
 require any additional crypto processing by the WTP.
 2 - Encrypt WEP 40: All packets to/from the mobile station must
 be encrypted using standard 40 bit WEP.
 3 - Encrypt WEP 128: All packets to/from the mobile station must
 be encrypted using standard 128 bit WEP.
 4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
 must be encrypted using 128 bit AES CCMP [7]
 5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
 be encrypted using TKIP and authenticated using Michael [17]
 Session Key: A 32 octet session key the WTP is to use when
 encrypting traffic to or decrypting traffic from the mobile
 station. The type of key is determined based on the Encryption
 Policy field.
 Pairwise TSC: The TSC to use for unicast packets transmitted to the
 mobile.
 Pairwise RSC: The RSC to use for unicast packets received from the
 mobile.
 Capabilities: A 16-bit field containing the 802.11 capabilities to
 use with the mobile.
 WLAN ID: An 8-bit value specifying the WLAN Identifier
 WME Mode: A 8-bit boolean used to identify whether the station is
 WME capable. A value of zero is used to indicate that the station
 is not WME capable, while a value of one means that the station is
 WME capable.
 802.11e Mode: A 8-bit boolean used to identify whether the station
 is 802.11e capable. A value of zero is used to indicate that the
 station is not 802.11e capable, while a value of one means that
 the station is 802.11e capable.
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 QoS: An 8-bit value specifying the QoS policy to enforce for the
 station. The following values are supported: PRC: TO CHECK
 0 - Silver (Best Effort)
 1 - Gold (Video)
 2 - Platinum (Voice)
 3 - Bronze (Background)
 Supported Rates: The supported rates to be used with the mobile
 station.
 VLAN Name: An optional variable string containing the VLAN Name on
 which the WTP is to locally bridge user data. Note this field is
 only valid with Local MAC WTPs.
11.7.1.2. IEEE 802.11 Mobile Session Key
 The Mobile Session Key Payload message element is sent when the AC
 determines that encryption of a mobile station must be performed in
 the WTP. This message element MUST NOT be present without the Add
 Mobile (see Section 11.7.1.1) message element, and MUST NOT be sent
 if the WTP had not specifically advertised support for the requested
 encryption scheme (see ???).
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address | Encryption Policy |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Encryption Policy | Session Key... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 105 for IEEE 802.11 Mobile Session Key
 Length: >= 11
 MAC Address: The mobile station's MAC Address
 Encryption Policy: The policy field informs the WTP how to handle
 packets from/to the mobile station. The following values are
 supported:
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 0 - Encrypt WEP 104: All packets to/from the mobile station must
 be encrypted using standard 104 bit WEP.
 1 - Clear Text: All packets to/from the mobile station do not
 require any additional crypto processing by the WTP.
 2 - Encrypt WEP 40: All packets to/from the mobile station must
 be encrypted using standard 40 bit WEP.
 3 - Encrypt WEP 128: All packets to/from the mobile station must
 be encrypted using standard 128 bit WEP.
 4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
 must be encrypted using 128 bit AES CCMP [7]
 5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
 be encrypted using TKIP and authenticated using Michael [17]
 Session Key: The session key the WTP is to use when encrypting
 traffic to/from the mobile station.
11.7.1.3. Station QoS Profile
 The Station QoS Profile Payload message element contains the maximum
 802.11e priority tag that may be used by the station. Any packets
 received that exceeds the value encoded in this message element must
 either be dropped or tagged using the maximum value permitted by to
 the user. The priority tag must be between zero (0) and seven (7).
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address | 802.1P Precedence Tag |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 140 for IEEE 802.11 Station QOS Profile
 Length: 12
 MAC Address: The mobile station's MAC Address
 802.1P Precedence Tag: The maximum 802.1P precedence value that the
 WTP will allow in the TID field in the extended 802.11e QOS Data
 header.
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11.7.1.4. IEEE 802.11 Update Mobile QoS
 The Update Mobile QoS message element is used to change the Quality
 of Service policy on the WTP for a given mobile station.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Association ID | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address | QoS Profile | Vlan Identifier |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | DSCP Tag | 802.1P Tag |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 106 for IEEE 802.11 Update Mobile QoS
 Length: 14
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Association ID: The 802.11 Association Identifier.
 MAC Address: The mobile station's MAC Address.
 QoS Profile: An 8-bit value specifying the QoS policy to enforce
 for the station. The following values are supported:
 0 - Silver (Best Effort)
 1 - Gold (Video)
 2 - Platinum (Voice)
 3 - Bronze (Background)
 VLAN Identifier: PRC.
 DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
 802.1P Tag: The 802.1P precedence value to use if packets are to be
 802.1P tagged.
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11.7.2. WTP Event Request
 This section contains the 802.11 specific message elements that are
 used with the WTP Event Request message.
11.7.2.1. IEEE 802.11 Statistics
 The statistics message element is sent by the WTP to transmit it's
 current statistics. The value contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Tx Fragment Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Tx Fragment Cnt| Multicast Tx Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Mcast Tx Cnt | Failed Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Failed Count | Retry Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Retry Count | Multiple Retry Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Multi Retry Cnt| Frame Duplicate Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Frame Dup Cnt | RTS Success Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |RTS Success Cnt| RTS Failure Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |RTS Failure Cnt| ACK Failure Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |ACK Failure Cnt| Rx Fragment Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Rx Fragment Cnt| Multicast RX Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Mcast Rx Cnt | FCS Error Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | FCS Error Cnt| Tx Frame Count |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Tx Frame Cnt | Decryption Errors |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Decryption Errs|
 +-+-+-+-+-+-+-+-+
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 Type: 38 for Statistics
 Length: 57
 Radio ID: An 8-bit value representing the radio.
 Tx Fragment Count: A 32-bit value representing the number of
 fragmented frames transmitted.
 Multicast Tx Count: A 32-bit value representing the number of
 multicast frames transmitted.
 Failed Count: A 32-bit value representing the transmit excessive
 retries.
 Retry Count: A 32-bit value representing the number of transmit
 retries.
 Multiple Retry Count: A 32-bit value representing the number of
 transmits that required more than one retry.
 Frame Duplicate Count: A 32-bit value representing the duplicate
 frames received.
 RTS Success Count: A 32-bit value representing the number of
 successfully transmitted Ready To Send (RTS).
 RTS Failure Count: A 32-bit value representing the failed
 transmitted RTS.
 ACK Failure Count: A 32-bit value representing the number of failed
 acknowledgements.
 Rx Fragment Count: A 32-bit value representing the number of
 fragmented frames received.
 Multicast RX Count: A 32-bit value representing the number of
 multicast frames received.
 FCS Error Count: A 32-bit value representing the number of FCS
 failures.
 Decryption Errors: A 32-bit value representing the number of
 Decryption errors that occured on the WTP. Note that this field
 is only valid in cases where the WTP provides encryption/
 decryption services.
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11.8. 802.11 Control Messages
 This section will define LWAPP Control Messages that are specific to
 the IEEE 802.11 binding.
11.8.1. IEEE 802.11 WLAN Config Request
 The IEEE 802.11 WLAN Configuration Request is sent by the AC to the
 WTP in order to change services provided by the WTP. This control
 message is used to either create, update or delete a WLAN on the WTP.
 The IEEE 802.11 WLAN Configuration Request is sent as a result of
 either some manual admistrative process (e.g., deleting a WLAN), or
 automatically to create a WLAN on an WTP. When sent automatically to
 create a WLAN, this control message is sent after the LWAPP
 Configuration Request message has been received by the WTP.
 Upon receiving this control message, the WTP will modify the
 necessary services, and transmit an IEEE 802.11 WLAN Configuration
 Response.
 An WTP MAY provide service for more than one WLAN, therefore every
 WLAN is identified through a numerical index. For instance, an WTP
 that is capable of supporting up to 16 SSIDs, could accept up to 16
 IEEE 802.11 WLAN Configuration Request messages that include the Add
 WLAN message element.
 Since the index is the primary identifier for a WLAN, an AC SHOULD
 attempt to ensure that the same WLAN is identified through the same
 index number on all of its WTPs. An AC that does not follow this
 approach MUST find some other means of maintaining a WLAN Identifier
 to SSID mapping table.
 The following subsections define the message elements that are value
 for this LWAPP operation. Only one message MUST be present.
11.8.1.1. IEEE 802.11 Add WLAN
 The Add WLAN message element is used by the AC to define a wireless
 LAN on the WTP. The value contains the following format:
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | WLAN Capability | WLAN ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Encryption Policy |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Key ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Key Index | Shared Key | WPA Data Len |WPA IE Data ...|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | RSN Data Len |RSN IE Data ...| Reserved .... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | WME Data Len |WME IE Data ...| 11e Data Len |11e IE Data ...|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | QoS | Auth Type |Broadcast SSID | Reserved... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | SSID ... |
 +-+-+-+-+-+-+-+-+
 Type: 7 for IEEE 802.11 Add WLAN
 Length: >= 298
 Radio ID: An 8-bit value representing the radio.
 WLAN Capability: A 16-bit value containing the capabilities to be
 advertised by the WTP within the Probe and Beacon messages.
 WLAN ID: A 16-bit value specifying the WLAN Identifier.
 Encryption Policy: A 32-bit value specifying the encryption scheme
 to apply to traffic to and from the mobile station.
 The following values are supported:
 0 - Encrypt WEP 104: All packets to/from the mobile station must
 be encrypted using standard 104 bit WEP.
 1 - Clear Text: All packets to/from the mobile station do not
 require any additional crypto processing by the WTP.
 2 - Encrypt WEP 40: All packets to/from the mobile station must
 be encrypted using standard 40 bit WEP.
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 3 - Encrypt WEP 128: All packets to/from the mobile station must
 be encrypted using standard 128 bit WEP.
 4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
 must be encrypted using 128 bit AES CCMP [7]
 5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
 be encrypted using TKIP and authenticated using Michael [17]
 6 - Encrypt CKIP: All packets to/from the mobile station must be
 encrypted using Cisco TKIP.
 Key: A 32 byte Session Key to use with the encryption policy.
 Key-Index: The Key Index associated with the key.
 Shared Key: A 1 byte boolean that specifies whether the key
 included in the Key field is a shared WEP key. A value of zero is
 used to state that the key is not a shared WEP key, while a value
 of one is used to state that the key is a shared WEP key.
 WPA Data Len: Length of the WPA IE.
 WPA IE: A 32 byte field containing the WPA Information Element.
 RSN Data Len: Length of the RSN IE.
 RSN IE: A 64 byte field containing the RSN Information Element.
 Reserved: A 49 byte reserved field, which MUST be set to zero (0).
 WME Data Len: Length of the WME IE.
 WME IE: A 32 byte field containing the WME Information Element.
 DOT11E Data Len: Length of the 802.11e IE.
 DOT11E IE: A 32 byte field containing the 802.11e Information
 Element.
 QOS: An 8-bit value specifying the QoS policy to enforce for the
 station.
 The following values are supported:
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 0 - Silver (Best Effort)
 1 - Gold (Video)
 2 - Platinum (Voice)
 3 - Bronze (Background)
 Auth Type: An 8-bit value specifying the station's authentication
 type.
 The following values are supported:
 0 - Open System
 1 - WEP Shared Key
 2 - WPA/WPA2 802.1X
 3 - WPA/WPA2 PSK
 Broadcast SSID: A boolean indicating whether the SSID is to be
 broadcast by the WTP. A value of zero disables SSID broadcast,
 while a value of one enables it.
 Reserved: A 40 byte reserved field.
 SSID: The SSID attribute is the service set identifier that will be
 advertised by the WTP for this WLAN.
11.8.1.2. IEEE 802.11 Delete WLAN
 The delete WLAN message element is used to inform the WTP that a
 previously created WLAN is to be deleted. The value contains the
 following fields:
 0 1 2
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | WLAN ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 28 for IEEE 802.11 Delete WLAN
 Length: 3
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 Radio ID: An 8-bit value representing the radio
 WLAN ID: A 16-bit value specifying the WLAN Identifier
11.8.1.3. IEEE 802.11 Update WLAN
 The Update WLAN message element is used by the AC to define a
 wireless LAN on the WTP. The value contains the following format:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | WLAN ID |Encrypt Policy |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Encryption Policy | Key... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Key ... |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Key Index | Shared Key | WLAN Capability |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 34 for IEEE 802.11 Update WLAN
 Length: 43
 Radio ID: An 8-bit value representing the radio.
 WLAN ID: A 16-bit value specifying the WLAN Identifier.
 Encryption Policy: A 32-bit value specifying the encryption scheme
 to apply to traffic to and from the mobile station.
 The following values are supported:
 0 - Encrypt WEP 104: All packets to/from the mobile station must
 be encrypted using standard 104 bit WEP.
 1 - Clear Text: All packets to/from the mobile station do not
 require any additional crypto processing by the WTP.
 2 - Encrypt WEP 40: All packets to/from the mobile station must
 be encrypted using standard 40 bit WEP.
 3 - Encrypt WEP 128: All packets to/from the mobile station must
 be encrypted using standard 128 bit WEP.
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 4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
 must be encrypted using 128 bit AES CCMP [7]
 5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
 be encrypted using TKIP and authenticated using Michael [17]
 6 - Encrypt CKIP: All packets to/from the mobile station must be
 encrypted using Cisco TKIP.
 Key: A 32 byte Session Key to use with the encryption policy.
 Key-Index: The Key Index associated with the key.
 Shared Key: A 1 byte boolean that specifies whether the key
 included in the Key field is a shared WEP key. A value of zero
 means that the key is not a shared WEP key, while a value of one
 is used to state that the key is a shared WEP key.
 WLAN Capability: A 16-bit value containing the capabilities to be
 advertised by the WTP within the Probe and Beacon messages.
11.8.2. IEEE 802.11 WLAN Config Response
 The IEEE 802.11 WLAN Configuration Response is sent by the WTP to the
 AC as an acknowledgement of the receipt of an IEEE 802.11 WLAN
 Configuration Request.
 This LWAPP control message does not include any message elements.
11.8.3. IEEE 802.11 WTP Event
 The IEEE 802.11 WTP Event LWAPP message is used by the WTP in order
 to report asynchronous events to the AC. There is no reply message
 expected from the AC, except that the message is acknowledged via the
 reliable transport.
 When the AC receives the IEEE 802.11 WTP Event, it will take whatever
 action is necessary, depending upon the message elements present in
 the message.
 The IEEE 802.11 WTP Event message MUST contain one of the following
 message element described in the next subsections.
11.8.3.1. IEEE 802.11 MIC Countermeasures
 The MIC Countermeasures message element is sent by the WTP to the AC
 to indicate the occurrence of a MIC failure.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | WLAN ID | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 61 for IEEE 802.11 MIC Countermeasures
 Length: 8
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP.
 WLAN ID: This 8-bit unsigned integer includes the WLAN Identifier,
 on which the MIC failure occurred.
 MAC Address: The MAC Address of the mobile station that caused the
 MIC failure.
11.8.3.2. IEEE 802.11 WTP Radio Fail Alarm Indication
 The WTP Radio Fail Alarm Indication message element is sent by the
 WTP to the AC when it detects a radio failure.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Type | Status | Pad |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 95 for WTP Radio Fail Alarm Indication
 Length: 4
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Type: The type of radio failure detected. The following values are
 supported:
 1 - Receiver
 2 - Transmitter
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 Status: An 8-bit boolean indicating whether the radio failure is
 being reported or cleared. A value of zero is used to clear the
 event, while a value of one is used to report the event.
 Pad: Reserved field MUST be set to zero (0).
11.9. Message Element Bindings
 The IEEE 802.11 Message Element binding has the following
 definitions:
 Conf Conf Conf Add
 Req Resp Upd Mobile
 IEEE 802.11 WTP WLAN Radio Configuration X X X
 IEEE 802.11 Rate Set X X
 IEEE 802.11 Multi-domain Capability X X X
 IEEE 802.11 MAC Operation X X X
 IEEE 802.11 Tx Power X X X
 IEEE 802.11 Tx Power Level X
 IEEE 802.11 Direct Sequence Control X X X
 IEEE 802.11 OFDM Control X X X
 IEEE 802.11 Supported Rates X X
 IEEE 802.11 Antenna X X X
 IEEE 802.11 CFP Status X X
 IEEE 802.11 Broadcast Probe Mode X X
 IEEE 802.11 WTP Mode and Type X? X
 IEEE 802.11 WTP Quality of Service X X
 IEEE 802.11 MIC Error Report From Mobile X
 IEEE 802.11 Update Mobile QoS X
 IEEE 802.11 Mobile Session Key X
11.9.1. IEEE 802.11 WTP WLAN Radio Configuration
 The WTP WLAN radio configuration is used by the AC to configure a
 Radio on the WTP. The message element value contains the following
 Fields:
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | Occupancy Limit |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | CFP Per | CFP Maximum Duration | BSS ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | BSS ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | BSS ID | Beacon Period | DTIM Per |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Country String |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Num Of BSSIDs |
 +-+-+-+-+-+-+-+-+
 Type: 8 for IEEE 802.11 WTP WLAN Radio Configuration
 Length: 20
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 Occupancy Limit: This attribute indicates the maximum amount of
 time, in TU, that a point coordinator MAY control the usage of the
 wireless medium without relinquishing control for long enough to
 allow at least one instance of DCF access to the medium. The
 default value of this attribute SHOULD be 100, and the maximum
 value SHOULD be 1000.
 CFP Period: The attribute describes the number of DTIM intervals
 between the start of CFPs.
 CFP Maximum Duration: The attribute describes the maximum duration
 of the CFP in TU that MAY be generated by the PCF.
 BSSID: The WLAN Radio's base MAC Address. For WTPs that support
 more than a single WLAN, the value of the WLAN Identifier is added
 to the last octet of the BSSID. Therefore, a WTP that supports 16
 WLANs MUST have 16 MAC Addresses reserved for it, and the last
 nibble is used to represent the WLAN ID.
 Beacon Period: This attribute specifies the number of TU that a
 station uses for scheduling Beacon transmissions. This value is
 transmitted in Beacon and Probe Response frames.
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 DTIM Period: This attribute specifies the number of beacon
 intervals that elapses between transmission of Beacons frames
 containing a TIM element whose DTIM Count field is 0. This value
 is transmitted in the DTIM Period field of Beacon frames.
 Country Code: This attribute identifies the country in which the
 station is operating. The first two octets of this string is the
 two character country code as described in document ISO/IEC 3166-
 1. The third octet MUST be one of the following:
 1. an ASCII space character, if the regulations under which the
 station is operating encompass all environments in the country,
 2. an ASCII 'O' character, if the regulations under which the
 station is operating are for an outdoor environment only, or
 3. an ASCII 'I' character, if the regulations under which the
 station is operating are for an indoor environment only
 Number of BSSIDs: This attribute contains the maximum number of
 BSSIDs supported by the WTP. This value restricts the number of
 logical networks supported by the WTP.
11.9.2. IEEE 802.11 Rate Set
 The rate set message element value is sent by the AC and contains the
 supported operational rates. It contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Rate Set |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 16 for IEEE 802.11 Rate Set
 Length: 4
 Radio ID: An 8-bit value representing the radio to configure.
 Rate Set: The AC generates the Rate Set that the WTP is to include
 in it's Beacon and Probe messages.
11.9.3. IEEE 802.11 Multi-domain Capability
 The multi-domain capability message element is used by the AC to
 inform the WTP of regulatory limits. The value contains the
 following fields.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | First Channel # |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Number of Channels | Max Tx Power Level |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 10 for IEEE 802.11 Multi-Domain Capability
 Length: 8
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 First Channnel #: This attribute indicates the value of the lowest
 channel number in the subband for the associated domain country
 string.
 Number of Channels: This attribute indicates the value of the total
 number of channels allowed in the subband for the associated
 domain country string.
 Max Tx Power Level: This attribute indicates the maximum transmit
 power, in dBm, allowed in the subband for the associated domain
 country string.
11.9.4. IEEE 802.11 MAC Operation
 The MAC operation message element is sent by the AC to set the 802.11
 MAC parameters on the WTP. The value contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | RTS Threshold |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Short Retry | Long Retry | Fragmentation Threshold |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Tx MSDU Lifetime |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Rx MSDU Lifetime |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 11 for IEEE 802.11 MAC Operation
 Length: 16
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 RTS Threshold: This attribute indicates the number of octets in an
 MPDU, below which an RTS/CTS handshake MUST NOT be performed. An
 RTS/CTS handshake MUST be performed at the beginning of any frame
 exchange sequence where the MPDU is of type Data or Management,
 the MPDU has an individual address in the Address1 field, and the
 length of the MPDU is greater than this threshold. Setting this
 attribute to be larger than the maximum MSDU size MUST have the
 effect of turning off the RTS/CTS handshake for frames of Data or
 Management type transmitted by this STA. Setting this attribute
 to zero MUST have the effect of turning on the RTS/CTS handshake
 for all frames of Data or Management type transmitted by this STA.
 The default value of this attribute MUST be 2347.
 Short Retry: This attribute indicates the maximum number of
 transmission attempts of a frame, the length of which is less than
 or equal to RTSThreshold, that MUST be made before a failure
 condition is indicated. The default value of this attribute MUST
 be 7.
 Long Retry: This attribute indicates the maximum number of
 transmission attempts of a frame, the length of which is greater
 than dot11RTSThreshold, that MUST be made before a failure
 condition is indicated. The default value of this attribute MUST
 be 4.
 Fragmentation Threshold: This attribute specifies the current
 maximum size, in octets, of the MPDU that MAY be delivered to the
 PHY. An MSDU MUST be broken into fragments if its size exceeds
 the value of this attribute after adding MAC headers and trailers.
 An MSDU or MMPDU MUST be fragmented when the resulting frame has
 an individual address in the Address1 field, and the length of the
 frame is larger than this threshold. The default value for this
 attribute MUST be the lesser of 2346 or the aMPDUMaxLength of the
 attached PHY and MUST never exceed the lesser of 2346 or the
 aMPDUMaxLength of the attached PHY. The value of this attribute
 MUST never be less than 256.
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 Tx MSDU Lifetime: This attribute speficies the elapsed time in TU,
 after the initial transmission of an MSDU, after which further
 attempts to transmit the MSDU MUST be terminated. The default
 value of this attribute MUST be 512.
 Rx MSDU Lifetime: This attribute specifies the elapsed time in TU,
 after the initial reception of a fragmented MMPDU or MSDU, after
 which further attempts to reassemble the MMPDU or MSDU MUST be
 terminated. The default value MUST be 512.
11.9.5. IEEE 802.11 Tx Power
 The Tx power message element value is bi-directional. When sent by
 the WTP, it contains the current power level of the radio in
 question. When sent by the AC, it contains the power level the WTP
 MUST adhere to.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | Current Tx Power |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 12 for IEEE 802.11 Tx Power
 Length: 4
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 Current Tx Power: This attribute contains the transmit output power
 in mW.
11.9.6. IEEE 802.11 Tx Power Level
 The Tx power level message element is sent by the WTP and contains
 the different power levels supported. The value contains the
 following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Num Levels | Power Level [n] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 13 for IEEE 802.11 Tx Power Level
 Length: >= 4
 Radio ID: An 8-bit value representing the radio to configure.
 Num Levels: The number of power level attributes.
 Power Level: Each power level fields contains a supported power
 level, in mW.
11.9.7. IEEE 802.11 Direct Sequence Control
 The direct sequence control message element is a bi-directional
 element. When sent by the WTP, it contains the current state. When
 sent by the AC, the WTP MUST adhere to the values. This element is
 only used for 802.11b radios. The value has the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | Current Chan | Current CCA |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Energy Detect Threshold |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 14 for IEEE 802.11 Direct Sequence Control
 Length: 8
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 Current Channel: This attribute contains the current operating
 frequency channel of the DSSS PHY.
 Current CCA: The current CCA method in operation. Valid values
 are:
 1 - energy detect only (edonly)
 2 - carrier sense only (csonly)
 4 - carrier sense and energy detect (edandcs)
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 8 - carrier sense with timer (cswithtimer)
 16 - high rate carrier sense and energy detect (hrcsanded)
 Energy Detect Threshold: The current Energy Detect Threshold being
 used by the DSSS PHY.
11.9.8. IEEE 802.11 OFDM Control
 The OFDM control message element is a bi-directional element. When
 sent by the WTP, it contains the current state. When sent by the AC,
 the WTP MUST adhere to the values. This element is only used for
 802.11a radios. The value contains the following fields:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Reserved | Current Chan | Band Support |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | TI Threshold |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 15 for IEEE 802.11 OFDM Control
 Length: 8
 Radio ID: An 8-bit value representing the radio to configure.
 Reserved: MUST be set to zero
 Current Channel: This attribute contains the current operating
 frequency channel of the OFDM PHY.
 Band Supported: The capability of the OFDM PHY implementation to
 operate in the three U-NII bands. Coded as an integer value of a
 three bit field as follows:
 Bit 0 - capable of operating in the lower (5.15-5.25 GHz) U-NII
 band
 Bit 1 - capable of operating in the middle (5.25-5.35 GHz) U-NII
 band
 Bit 2 - capable of operating in the upper (5.725-5.825 GHz) U-NII
 band
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 For example, for an implementation capable of operating in the
 lower and mid bands this attribute would take the value
 TI Threshold: The Threshold being used to detect a busy medium
 (frequency). CCA MUST report a busy medium upon detecting the
 RSSI above this threshold.
11.9.9. IEEE 802.11 Antenna
 The antenna message element is communicated by the WTP to the AC to
 provide information on the antennas available. The AC MAY use this
 element to reconfigure the WTP's antennas. The value contains the
 following fields:
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Diversity | Combiner | Antenna Cnt |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Antenna Selection [0..N] |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 41 for IEEE 802.11 Antenna
 Length: >= 8
 Radio ID: An 8-bit value representing the radio to configure.
 Diversity: An 8-bit value specifying whether the antenna is to
 provide receive diversity. The following values are supported:
 0 - Disabled
 1 - Enabled (may only be true if the antenna can be used as a
 receive antenna)
 Combiner: An 8-bit value specifying the combiner selection. The
 following values are supported:
 1 - Sectorized (Left)
 2 - Sectorized (Right)
 3 - Omni
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 4 - Mimo
 Antenna Count: An 8-bit value specifying the number of Antenna
 Selection fields.
 Antenna Selection: One 8-bit antenna configuration value per
 antenna in the WTP. The following values are supported:
 1 - Internal Antenna
 2 - External Antenna
11.9.10. IEEE 802.11 Supported Rates
 The supported rates message element is sent by the WTP to indicate
 the rates that it supports. The value contains the following fields.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Supported Rates |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 16 for IEEE 802.11 Supported Rates
 Length: 4
 Radio ID: An 8-bit value representing the radio.
 Supported Rates: The WTP includes the Supported Rates that it's
 hardware supports. The format is identical to the Rate Set
 message element.
11.9.11. IEEE 802.11 CFP Status
 The CFP Status message element is sent to provide the CF Polling
 configuration.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Status |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 48 for IEEE 802.11 CFP Status
 Length: 2
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Status: An 8-bit boolean containing the status of the CF Polling
 feature. A value of zero disables CFP Status, while a value of
 one enables it.
11.9.12. IEEE 802.11 WTP Mode and Type
 The WTP Mode and Type message element is used to configure an WTP to
 operate in a specific mode.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Mode | Type |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 54 for IEEE 802.11 WTP Mode and Type
 Length: 2
 Mode: An 8-bit value the type of information being sent. The
 following values are supported:
 0 - Split MAC
 2 - Local MAC
 Type: The type field is not currently used.
11.9.13. IEEE 802.11 Broadcast Probe Mode
 The Broadcast Probe Mode message element indicates whether an WTP
 will respond to NULL SSID probe requests. Since broadcast NULL
 probes are not sent to a specific BSSID, the WTP cannot know which
 SSID the sending station is querying. Therefore, this behavior must
 be global to the WTP.
 0
 0 1 2 3 4 5 6 7
 +-+-+-+-+-+-+-+-+
 | Status |
 +-+-+-+-+-+-+-+-+
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 Type: 51 for IEEE 802.11 Broadcast Probe Mode
 Length: 1
 Status: An 8-bit boolean indicating the status of whether an WTP
 shall response to a NULL SSID probe request. A value of zero
 disables NULL SSID probe response, while a value of one enables
 it.
11.9.14. IEEE 802.11 WTP Quality of Service
 The WTP Quality of Service message element value is sent by the AC to
 the WTP to communicate quality of service configuration information.
 0 1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | Tag Packets |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type: 57 for IEEE 802.11 WTP Quality of Service
 Length: 12
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 Tag Packets: An value indicating whether LWAPP packets should be
 tagged with for QoS purposes. The following values are currently
 supported:
 0 - Untagged
 1 - 802.1P
 2 - DSCP
 Immediately following the above header is the following data
 structure. This data structure will be repeated five times; once
 for every QoS profile. The order of the QoS profiles are Uranium,
 Platinum, Gold, Silver and Bronze.
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 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Queue Depth | CWMin | CWMax |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | CWMax | AIFS | CBR |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Dot1P Tag | DSCP Tag |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Queue Depth: The number of packets that can be on the specific QoS
 transmit queue at any given time.
 CWMin: The Contention Window minimum value for the QoS transmit
 queue.
 CWMax: The Contention Window maximum value for the QoS transmit
 queue.
 AIFS: The Arbitration Inter Frame Spacing to use for the QoS
 transmit queue.
 CBR: The CBR value to observe for the QoS transmit queue.
 Dot1P Tag: The 802.1P precedence value to use if packets are to be
 802.1P tagged.
 DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
11.9.15. IEEE 802.11 MIC Error Report From Mobile
 The MIC Error Report From Mobile message element is sent by an AC to
 an WTP when it receives a MIC failure notification, via the Error bit
 in the EAPOL-Key frame.
 0 1 2 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Client MAC Address |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Client MAC Address | BSSID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | BSSID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Radio ID | WLAN ID |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Type: 79 for IEEE 802.11 MIC Error Report From Mobile
 Length: 14
 Client MAC Address: The Client MAC Address of the station reporting
 the MIC failure.
 BSSID: The BSSID on which the MIC failure is being reported.
 Radio ID: The Radio Identifier, typically refers to some interface
 index on the WTP
 WLAN ID: The WLAN ID on which the MIC failure is being reported.
11.10. IEEE 802.11 Message Element Values
 This section lists IEEE 802.11 specific values for any generic LWAPP
 message elements which include fields whose values are technology
 specific.
 IEEE 802.11 uses the following values:
 4 - Encrypt AES-CCMP 128: WTP supports AES-CCMP, as defined in [7].
 5 - Encrypt TKIP-MIC: WTP supports TKIP and Michael, as defined in
 [17].
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12. LWAPP Protocol Timers
 An WTP or AC that implements LWAPP discovery MUST implement the
 following timers.
12.1. MaxDiscoveryInterval
 The maximum time allowed between sending discovery requests from the
 interface, in seconds. Must be no less than 2 seconds and no greater
 than 180 seconds.
 Default: 20 seconds.
12.2. SilentInterval
 The minimum time, in seconds, an WTP MUST wait after failing to
 receive any responses to its discovery requests, before it MAY again
 send discovery requests.
 Default: 30
12.3. NeighborDeadInterval
 The minimum time, in seconds, an WTP MUST wait without having
 received Echo Responses to its Echo Requests, before the destination
 for the Echo Request may be considered dead. Must be no less than
 2*EchoInterval seconds and no greater than 240 seconds.
 Default: 60
12.4. EchoInterval
 The minimum time, in seconds, between sending echo requests to the AC
 with which the WTP has joined.
 Default: 30
12.5. DiscoveryInterval
 The minimum time, in seconds, that an WTP MUST wait after receiving a
 Discovery Response, before sending a join request.
 Default: 5
12.6. RetransmitInterval
 The minimum time, in seconds, which a non-acknowledged LWAPP packet
 will be retransmitted.
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 Default: 3
12.7. ResponseTimeout
 The minimum time, in seconds, which an LWAPP Request message must be
 responded to.
 Default: 1
12.8. KeyLifetime
 The maximum time, in seconds, which an LWAPP session key is valid.
 Default: 28800
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13. LWAPP Protocol Variables
 An WTP or AC that implements LWAPP discovery MUST allow for the
 following variables to be configured by system management; default
 values are specified so as to make it unnecessary to configure any of
 these variables in many cases.
13.1. MaxDiscoveries
 The maximum number of discovery requests that will be sent after an
 WTP boots.
 Default: 10
13.2. DiscoveryCount
 The number of discoveries transmitted by a WTP to a single AC. This
 is a monotonically increasing counter.
13.3. RetransmitCount
 The number of retransmissions for a given LWAPP packet. This is a
 monotonically increasing counter.
13.4. MaxRetransmit
 The maximum number of retransmissions for a given LWAPP packet before
 the link layer considers the peer dead.
 Default: 5
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14. NAT Considerations
 There are two specific situations where a NAT system may be used in
 conjunction with LWAPP. The first consists of a configuration where
 the WTP is behind a NAT system. Given that all communication is
 initiated by the WTP, and all communication is performed over IP
 using a single UDP port, the protocol easily traverses NAT systems in
 this configuration.
 The second configuration is one where the AC sits behind a NAT and
 there are two main issues that exist in this situation. First, an AC
 communicates its interfaces, and associated WTP load on these
 interfaces, through the WTP Manager Control IP Address. This message
 element is currently mandatory, and if NAT compliance became an
 issue, it would be possible to either:
 1. Make the WTP Manager Control IP Address optional, allowing the WTP
 to simply use the known IP Address. However, note that this
 approach would eliminate the ability to perform load balancing of
 WTP across ACs, and therefore is not the recommended approach.
 2. Allow an AC to be able to configure a NAT'ed address for every
 associated AC that would generally be communicated in the WTP
 Manager Control IP Address message element.
 3. Require that if a WTP determines that the AC List message element
 consists of a set of IP Addresses that are different from the AC's
 IP Address it is currently communicating with, then assume that
 NAT is being enforced, and require that the WTP communicate with
 the original AC's IP Address (and ignore the WTP Manager Control
 IP Address message element(s)).
 Another issue related to having an AC behind a NAT system is LWAPP's
 support for the CAPWAP Objective to allow the control and data plane
 to be separated. In order to support this requirement, the LWAPP
 protocol defines the WTP Manager Data IP Address message element,
 which allows the AC to inform the WTP that the LWAPP data frames are
 to be forwarded to a separate IP Address. This feature MUST be
 disabled when an AC is behind a NAT. However, there is no easy way
 to provide some default mechanism that satisfies both the data/
 control separation and NAT objectives, as they directly conflict with
 each other. As a consequence, user intervention will be required to
 support such networks.
 LWAPP has a feature that allows for all of the ACs identities
 supporting a group of WTPs to be communicated through the AC List
 message element. This feature must be disabled when the AC is behind
 a NAT and the IP Address that is embedded would be invalid.
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 The LWAPP protocol has a feature that allows an AC to configure a
 static IP address on a WTP. The WTP Static IP Address Information
 message element provides such a function, however this feature SHOULD
 NOT be used in NAT'ed environments, unless the administrator is
 familiar with the internal IP addressing scheme within the WTP's
 private network, and does not rely on the public address seen by the
 AC.
 When a WTP detects the duplicate address condition, it generates a
 message to the AC, which includes the Duplicate IP Address message
 element. Once again, it is important to note that the IP Address
 embedded within this message element would be different from the
 public IP address seen by the AC.
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15. Security Considerations
 LWAPP uses either an authenticated key exchange or key agreement
 mechanism to ensure peer authenticity and establish fresh session
 keys to protect the LWAPP communications.
 The LWAPP protocol defines a join phase, which allows a WTP to bind a
 session with an AC. During this process, a session key is mutually
 derived, and secured either through an X.509 certificate or a pre-
 shared key. The resulting key exchange generates an encryption
 session key, which is used to encrypt the LWAPP control packets, and
 a key derivation key.
 During the established secure communication, the WTP and AC may rekey
 using the key update process, which is identical to the join phase,
 meaning the session keys are mutually derived. However, the exchange
 described for pre-shared session keys is always used for the key
 update, with the pre-shared key set to the derivation key created
 either during the join, or the last key update if one has occurred.
 The key update results in a new derivation key, which is used in the
 next key update, as well as an encryption session key to encrypt the
 LWAPP control packets.
 Replay protection of the Join Request is handled through an exchange
 of Nonces during the Join (or key update) phase. The Join Request
 includes an XNonce, which is included in the AC's authenticated Join
 Replys encrypted ANonce message element, allowing for the two
 messages to be bound. Upon receipt of the Join Reply, the WTP
 generates the WNonce, and generates a set of session keys using a KDF
 function. One of these keys is used to MIC the Join ACK. The AC
 responds with a Join Confirm, which must also include a MIC, and
 therefore be capable of deriving the same set of session keys.
 In both the X.509 certificate and pre-shared key modes, an
 initialization vector is created through the above mentioned KDF
 function. The IV and the KDF created encryption key are used to
 encrypt the LWAPP control frames.
 Given that authentication in the Join exchange does not occur until
 the WTP transmits the Join ACK message, it is crucial that an AC not
 delete any state for a WTP it is service until an authentication Join
 ACK has been received. Otherwise, a potential Denial of Service
 attack exists, whereby sending a spoofed Join Request for a valid WTP
 would cause the AC to reset the WTP's connection.
 It is important to note that Perfect Forward Secrecy is not a
 requirement for the LWAPP protocol.
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 Note that the LWAPP protocol does not add any new vulnerabilities to
 802.11 infrastructure that makes use of WEP for encryption purposes.
 However, implementors SHOULD discourage the use of WEP to allow the
 market to move towards technically sound cryptographic solutions,
 such as 802.11i.
15.1. Certificate based Session Key establishment
 LWAPP uses public key cryptography to ensure trust between the WTP
 and the AC. One question that periodically arises is why the Join
 Request is not signed. Signing this request would not be optimal for
 the following reasons:
 1. The Join Request is replayable, so a signature doesn't provide
 much protection unless the switches keep track of all previous
 Join Requests from a given WTP.
 2. Replay detection is handled during the Join Reply and Join ACK
 messages.
 3. A signed Join Request provides a potential Denial of Service
 attack on the AC, which would have to authenticate each
 (potentially malicious) message.
 The WTP-Certificate that is included in the Join Request MUST be
 validated by the AC. It is also good practice that the AC perform
 some form of authorization, ensuring that the WTP in question is
 allowed to establish an LWAPP session with it.
15.2. PSK based Session Key establishment
 Use of a fixed shared secret of limited entropy (for example, a PSK
 that is relatively short, or was chosen by a human and thus may
 contain less entropy than its length would imply) may allow an
 attacker to perform a brute-force or dictionary attack to recover the
 secret.
 It is RECOMMENDED that implementations that allow the administrator
 to manually configure the PSK also provide a functionality for
 generating a new random PSK, taking RFC 1750 [4] into account.
 Since the key generation does not expose the nonces in plaintext,
 there are no practical passive attacks possible.
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16. IANA Considerations
 This document requires no action by IANA.
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17. Acknowledgements
 The authors wish to thank Michael Vakulenko for contributing text
 that describes how LWAPP can be used over a layer 3 (IP) network.
 The authors would like to thanks Russ Housley and Charles Clancy for
 their assistance in provide a security review of the LWAPP
 specification. Charles' review can be found at [12].
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18. IPR Statement
 The IETF has been notified of intellectual property rights claimed in
 regard to some or all of the specification contained in this
 document. For more information consult the online list of claimed
 rights.
 Please refer to http://www.ietf.org/ietf/IPR for more information.
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19. References
19.1. Normative References
 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
 Levels", BCP 14, RFC 2119, March 1997.
 [2] National Institute of Standards and Technology, "Advanced
 Encryption Standard (AES)", FIPS PUB 197, November 2001,
 <http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
 [3] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-
 MAC (CCM)", RFC 3610, September 2003.
 [4] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
 Recommendations for Security", RFC 1750, December 1994.
 [5] Manner, J. and M. Kojo, "Mobility Related Terminology",
 RFC 3753, June 2004.
 [6] "Information technology - Telecommunications and information
 exchange between systems - Local and metropolitan area networks
 - Specific requirements - Part 11: Wireless LAN Medium Access
 Control (MAC) and Physical Layer (PHY) specifications",
 IEEE Standard 802.11, 1999,
 <http://standards.ieee.org/getieee802/download/
 802.11-1999.pdf>.
 [7] "Information technology - Telecommunications and information
 exchange between systems - Local and metropolitan area networks
 - Specific requirements - Part 11: Wireless LAN Medium Access
 Control (MAC) and Physical Layer (PHY) specifications Amendment
 6: Medium Access Control (MAC) Security Enhancements",
 IEEE Standard 802.11i, July 2004, <http://standards.ieee.org/
 getieee802/download/802.11i-2004.pdf>.
 [8] Clark, D., "IP datagram reassembly algorithms", RFC 815,
 July 1982.
 [9] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES)
 Key Wrap Algorithm", RFC 3394, September 2002.
 [10] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
 Public Key Infrastructure Certificate and Certificate
 Revocation List (CRL) Profile", RFC 3280, April 2002.
 [11] "Netscape Certificate Extensions Specification",
 <http://wp.netscape.com/eng/security/comm4-cert-exts.html>.
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 [12] Clancy, C., "Security Review of the Light Weight Access Point
 Protocol", May 2005,
 <http://www.cs.umd.edu/~clancy/docs/lwapp-review.pdf>.
19.2. Informational References
 [13] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
 line Database", RFC 3232, January 2002.
 [14] Bradner, S., "The Internet Standards Process -- Revision 3",
 BCP 9, RFC 2026, October 1996.
 [15] Kent, S. and R. Atkinson, "Security Architecture for the
 Internet Protocol", RFC 2401, November 1998.
 [16] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
 for Message Authentication", RFC 2104, February 1997.
 [17] "WiFi Protected Access (WPA) rev 1.6", April 2003.
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Authors' Addresses
 Pat R. Calhoun
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 Phone: +1 408-853-5269
 Email: pcalhoun@cisco.com
 Bob O'Hara
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 Phone: +1 408-853-5513
 Email: bob.ohara@cisco.com
 Rohit Suri
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 Phone: +1 408-853-5548
 Email: rsuri@cisco.com
 Nancy
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134
 Phone: +1 408-853-0532
 Email: ncamwing@cisco.com
 Scott Kelly
 Facetime Communications
 1159 Triton Dr
 Foster City, CA 94404
 Phone: +1 650 572-5846
 Email: scott@hyperthought.com
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 Michael Glenn Williams
 Nokia, Inc.
 313 Fairchild Drive
 Mountain View, CA 94043
 Phone: +1 650-714-7758
 Email: Michael.G.Williams@Nokia.com
 Sue Hares
 Nexthop Technologies, Inc.
 825 Victors Way, Suite 100
 Ann Arbor, MI 48108
 Phone: +1 734 222 1610
 Email: shares@nexthop.com
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Full Copyright Statement
 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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Calhoun, et al. Expires September 3, 2007 [Page 137]
Lightweight Access Point Protocol draft-ohara-capwap-lwapp-04

Lightweight Access Point Protocol
draft-ohara-capwap-lwapp-04
