Network Working Group G. Halwasia
Internet-Draft S. Bhandari
Intended status: Standards Track W. Dec
Expires: September 12, 2013 Cisco Systems
March 11, 2013
Client Link-layer Address Option in DHCPv6
draft-ietf-dhc-dhcpv6-client-link-layer-addr-opt-05
Abstract
This document specifies the format and mechanism that is to be used
for encoding client link-layer address in DHCPv6 Relay-Forward
messages by defining a new DHCPv6 Client Link-layer Address option.
Requirements Language
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 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 12, 2013.
Copyright Notice
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Background and Scenario . . . . . . . . . . . . . . . 2
3. DHCPv6 Client Link-layer Address Option . . . . . . . . . . . 3
4. DHCPv6 Relay Agent Behavior . . . . . . . . . . . . . . . . . 4
5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . 4
6. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This specification defines an optional mechanism and the related
DHCPv6 option to allow first-hop DHCPv6 relay agents (relay agents
that are connected to the same link as the client) to provide the
client's link-layer address in the DHCPv6 messages being sent towards
the server.
2. Problem Background and Scenario
DHCPv4 protocol specification [RFC2131] provides a way to specify the
client link-layer address in the DHCPv4 message header. DHCPv4
message header has 'htype' and 'chaddr' fields to specify client
link-layer address type and link-layer address respectively. The
client link-layer address thus learnt can be used by DHCPv4 server
and relay in different ways. In some of the deployments DHCPv4
servers use 'chaddr' as a customer identifier and a key for lookup in
the client lease database.
With the incremental deployment of IPv6 to existing IPv4 networks,
which results in a dual-stack network environment, there will be
devices that act as both DHCPv4 and DHCPv6 clients. In service
provider deployments, a typical DHCPv4 implementation will use the
client link-layer address as one of the keys to build DHCP client
lease database. In dual stack scenarios operators need to be able to
associate DHCPv4 and DHCPv6 messages with the same client interface,
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based on an identifier that is common to the interface. The client
link-layer address is such an identifier.
Currently, the DHCPv6 protocol specification [RFC3315] does not
define a way to communicate the client link-layer address to the DHCP
server in cases where the DHCP server is not connected to the same
network link as the DHCP client. DHCPv6 protocol specification
mandates all clients to prepare and send DUID as the client
identifier option in all the DHCPv6 message exchange. However none
of these methods provide a simple way to extract client's link-layer
address. This presents a problem to an operator who is using an
existing DHCPv4 system with the client link-layer address as the
customer identifier, and desires to correlate DHCPv6 assignments
using the same identifier. [RFC4361] describes a mechanism for using
the same DUID in both DHCPv4 and DHCPv6. Unfortunately, this
specification requires modification of existing DHCPv4 clients, and
has not seen broad adoption in the industry (indeed, we are not aware
of any commercial implementations).
Providing an option in DHCPv6 Relay-Forward messages to carry client
link-layer address explicitly will help above mentioned scenarios.
For example, it can be used along with other identifiers to associate
DHCPv4 and DHCPv6 messages from a dual stack client. Further, having
client link-layer address in DHCPv6 will help in proving additional
information in event debugging and logging related to the client at
relay and server. The proposed option may be used in wide range of
networks, two notable deployment models are service provider and
enterprise network environments.
3. DHCPv6 Client Link-layer Address Option
The format of the DHCPv6 Client Link-layer Address option is shown
below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_LINKLAYER_ADDR | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| link-layer type (16 bits) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| link-layer address (variable length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_CLIENT_LINKLAYER_ADDR (TBD)
option-length: 2 + length of link-layer address
link-layer type: Client Link-layer address type. The link-layer
type MUST be a valid hardware type assigned
by the IANA, as described in [RFC0826]
link-layer address: Client Link-layer address.
4. DHCPv6 Relay Agent Behavior
DHCPv6 Relay agents which receive messages originating from clients
(for example Solicit and Request, but not, for example, Relay-Forward
or Advertise) MAY include the link-layer source address of the
received DHCPv6 message in Client Link-layer Address option in
relayed DHCPv6 Relay-Forward messages. The DHCPv6 Relay agent
behavior can depend on configuration that decides whether the Client
Link-layer Address option needs to be included.
5. DHCPv6 Server Behavior
If DHCPv6 Server is configured to store or use client link-layer
address, it SHOULD look for the client link-layer address option in
the Relay-Forward DHCP message of the DHCPv6 Relay agent closest to
the client. The mechanism described in this document is not
necessary in the case where the DHCPv6 Server is connected to the
same network link as the client, because the server can obtain the
link-layer address from the link-layer header of the DHCPv6 message.
If the DHCP server receives a Client Link-layer Address option
anywhere in any encapsulated message that is not a Relay-Forward DHCP
message, the server MUST silently ignore that option.
There is no requirement that a server return this option and its data
in a downstream DHCP message.
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6. DHCPv6 Client Behavior
Client Link-layer Address option is only exchanged between the relay
agents and the servers. DHCPv6 clients are not aware of the usage of
Client Link-layer Address option. DHCPv6 client MUST NOT send Client
Link-layer Address option, and MUST ignore Client Link-layer Address
option if received.
7. IANA Considerations
IANA is requested to assign an option code to
OPTION_CLIENT_LINKLAYER_ADDR from the "DHCP Option Codes" registry
(http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-
parameters.xml).
8. Security Considerations
It is possible for a rogue DHCPv6 relay agent to insert an incorrect
Client Link Layer Address option for malicious purposes. A DHCPv6
client can also pose as a rogue DHCP relay agent, sending a Relay-
Forward message containing an incorrect Client Link Layer Address
option. In either case, it would be possible for a DHCPv6 client to
masquerade as the same device as a DHCPv4 client, when in fact the
two are distinct.
One possible attack that could be accomplished using this masquerade
would be in the case where a DHCPv4 client is using DHCPv4 to do a
Dynamic DNS update to install an A record so that it can be reached
by other nodes [RFC4702]. A masquerading DHCPv6 client could use
DHCPv6 to install an AAAA record with the same name [RFC4704]. Dual-
stack nodes attempting to connect to the DHCPv4 client might then be
tricked into connecting to the masquerading DHCPv6 client instead.
It is possible that there are other attacks that could be
accomplished using this masquerading technique, although the authors
are not aware of any. To prevent masquerades of this sort, DHCP
server administrators are strongly advised to configure DHCP servers
that use this option to communicate with their relay agents using
IPsec as described in Section 21.1 of [RFC3315].
In some networks, it may be the case that the operator of the
physical network and the provider of connectivity over that network
are administratively separate, such that the client link-layer
address option would reveal information to one or the other party
that they do not need and could not otherwise obtain. It is also
possible in some cases that a relay agent might communicate with a
DHCP server over an open network where eavesdropping would be
possible. In these cases, it is strongly recommended, in order to
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protect end-user privacy, that network operators use IPsec to provide
confidentiality for messages between the relay agent and DHCP server.
9. Acknowledgements
Many thanks to Ted Lemon, Bernie Volz, Hemant Singh, Simon Hobson,
Tina TSOU, Andre Kostur, Chuck Anderson, Steinar Haug, Niall
O'Reilly, Jarrod Johnson, Tomek Mrugalski and Vincent Zimmer for
their input and review.
10. References
10.1. Normative References
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
10.2. Informative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host
Configuration Protocol (DHCP) Client Fully Qualified
Domain Name (FQDN) Option", RFC 4702, October 2006.
[RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN)
Option", RFC 4704, October 2006.
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Authors' Addresses
Gaurav Halwasia
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Phone: +91 80 4429 2703
Email: ghalwasi@cisco.com
Shwetha Bhandari
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Phone: +91 80 4429 2627
Email: shwethab@cisco.com
Wojciech Dec
Cisco Systems
Haarlerbergweg 13-19
1101 CH Amsterdam, Amsterdam 560 087
The Netherlands
Email: wdec@cisco.com
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