Modification to Default Values of SOL_MAX_RT and INF_MAX_RT
RFC 7083

Internet Engineering Task Force (IETF) R. Droms
Request for Comments: 7083 Cisco Systems
Updates: 3315 November 2013
Category: Standards Track
ISSN: 2070-1721
 Modification to Default Values of SOL_MAX_RT and INF_MAX_RT
Abstract
 This document updates RFC 3315 by redefining the default values for
 SOL_MAX_RT and INF_MAX_RT and defining options through which a DHCPv6
 server can override the client's default value for SOL_MAX_RT and
 INF_MAX_RT with new values.
Status of This Memo
 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF). It represents the consensus of the IETF community. It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG). Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7083.
Copyright Notice
 Copyright (c) 2013 IETF Trust and the persons identified as the
 document authors. All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document. Please review these documents
 carefully, as they describe your rights and restrictions with respect
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 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
Droms Standards Track [Page 1]
RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
 3. Updates to SOL_MAX_RT and INF_MAX_RT in RFC 3315 . . . . . . 2
 4. SOL_MAX_RT option . . . . . . . . . . . . . . . . . . . . . . 3
 5. INF_MAX_RT Option . . . . . . . . . . . . . . . . . . . . . . 4
 6. Updates for SOL_MAX_RT and INF_MAX_RT Options to RFC 3315 . . 4
 7. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 5
 8. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . 6
 9. DHCPv6 Relay Agent Behavior . . . . . . . . . . . . . . . . . 6
 10. Security Considerations . . . . . . . . . . . . . . . . . . . 6
 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
 13.1. Normative References . . . . . . . . . . . . . . . . . . 7
 13.2. Informative References . . . . . . . . . . . . . . . . . 7
1. Introduction
 Section 5.5 of the DHCPv6 specification [RFC3315] defines the default
 values of SOL_MAX_RT and INF_MAX_RT to be 120 seconds. In some
 circumstances, these defaults will lead to an unacceptably high
 volume of aggregated traffic at a DHCPv6 server.
 The change to SOL_MAX_RT is in response to DHCPv6 message rates
 observed on a DHCPv6 server in a deployment in which many DHCPv6
 clients are sending Solicit messages, but the DHCPv6 server has been
 configured not to respond to those Solicit messages. While no
 explicit observations of traffic due to INF_MAX_RT have been
 conducted, this document updates INF_MAX_RT for consistency with
 SOL_MAX_RT.
2. 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].
3. Updates to SOL_MAX_RT and INF_MAX_RT in RFC 3315
 This document changes Section 5.5 of RFC 3315 as follows:
 OLD:
 SOL_MAX_RT 120 secs Max Solicit timeout value
 NEW:
 SOL_MAX_RT 3600 secs Max Solicit timeout value
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RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
 OLD:
 INF_MAX_RT 120 secs Max Information-request timeout value
 NEW:
 INF_MAX_RT 3600 secs Max Information-request timeout value
 With this change, a DHCPv6 client that does not receive a
 satisfactory response will send Solicit or Information-request
 messages with the same initial frequency and exponential backoff as
 specified in Sections 17.1.2 and 18.1.5 of RFC 3315. However, the
 long-term behavior of these DHCPv6 clients will be to send a Solicit
 or Information-request message every 3600 seconds rather than every
 120 seconds, significantly reducing the aggregated traffic at the
 DHCPv6 server.
4. SOL_MAX_RT option
 A DHCPv6 server sends the SOL_MAX_RT option to a client to override
 the default value of SOL_MAX_RT. The value of SOL_MAX_RT in the
 option replaces the default value defined in Section 3. One use for
 the SOL_MAX_RT option is to set a longer value for SOL_MAX_RT, which
 reduces the Solicit traffic from a client that has not received a
 response to its Solicit messages.
 The format of the SOL_MAX_RT option is:
 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-code | option-len |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | SOL_MAX_RT value |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 option-code OPTION_SOL_MAX_RT (82)
 option-len 4
 SOL_MAX_RT value Overriding value for SOL_MAX_RT
 in seconds; MUST be in range:
 60 <= "value" <= 86400 (1 day)
 Figure 1: SOL_MAX_RT Option Format
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RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
5. INF_MAX_RT Option
 A DHCPv6 server sends the INF_MAX_RT option to a client to override
 the default value of INF_MAX_RT. The value of INF_MAX_RT in the
 option replaces the default value defined in Section 3. One use for
 the INF_MAX_RT option is to set a longer value for INF_MAX_RT, which
 reduces the Information-request traffic from a client that has not
 received a response to its Information-request messages.
 The format of the INF_MAX_RT option is:
 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-code | option-len |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | INF_MAX_RT value |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 option-code OPTION_INF_MAX_RT (83)
 option-len 4
 INF_MAX_RT value Overriding value for INF_MAX_RT
 in seconds; MUST be in range:
 60 <= "value" <= 86400 (1 day)
 Figure 2: INF_MAX_RT Option Format
6. Updates for SOL_MAX_RT and INF_MAX_RT Options to RFC 3315
 Update to RFC 3315, Section 17.1.3:
 OLD:
 The client MUST ignore any Advertise message that includes a Status
 Code option containing the value NoAddrsAvail, with the exception
 that the client MAY display the associated status message to the
 user.
 NEW:
 The client MUST ignore any Advertise message that includes a Status
 Code option containing the value NoAddrsAvail, with the exception
 that the client MUST process an included SOL_MAX_RT option, MUST
 process an included INF_MAX_RT option, and MAY display the
 associated status message to the user.
Droms Standards Track [Page 4]
RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
 Update to RFC 3315, Section 17.2.2:
 OLD:
 If the server will not assign any addresses to any IAs in a
 subsequent Request from the client, the server MUST send an
 Advertise message to the client that includes only a Status Code
 option with code NoAddrsAvail and a status message for the user, a
 Server Identifier option with the server's DUID, and a Client
 Identifier option with the client's DUID.
 NEW:
 If the server will not assign any addresses to any IAs in a
 subsequent Request from the client, the server MUST send an Advertise
 message to the client that includes only a Status Code option with
 code NoAddrsAvail and a status message for the user, a Server
 Identifier option with the server's DUID, a Client Identifier option
 with the client's DUID, and (optionally) SOL_MAX_RT and/or INF_MAX_RT
 options.
 Update to RFC 3315, Section 14 (Add text, clarifying client behavior
 while waiting for a response from a server):
 NEW:
 A client is not expected to listen for a response during the entire
 period between transmission of Solicit or Information-request
 messages.
7. DHCPv6 Client Behavior
 A DHCPv6 client MUST include the SOL_MAX_RT option code in any Option
 Request option [RFC3315] it sends as required by RFC 3315.
 A DHCPv6 client MUST include the INF_MAX_RT option code in any Option
 Request option it sends as required by RFC 3315.
 A DHCPv6 client MUST silently ignore any SOL_MAX_RT or INF_MAX_RT
 option values that are less than 60 or more than 86400.
 If a DHCPv6 client receives a message containing a SOL_MAX_RT option
 that has a valid value for SOL_MAX_RT, the client MUST set its
 internal SOL_MAX_RT parameter to the value contained in the
 SOL_MAX_RT option. This value of SOL_MAX_RT is then used by the
 retransmission mechanism defined in Sections 14 and 17.1.2 of RFC
 3315.
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RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
 If a DHCPv6 client receives a message containing an INF_MAX_RT option
 that has a valid value for INF_MAX_RT, the client MUST set its
 internal INF_MAX_RT parameter to the value contained in the
 INF_MAX_RT option. This value of INF_MAX_RT is then used by the
 retransmission mechanism defined in Sections 14 and 18.1.5 of RFC
 3315.
 Updated SOL_MAX_RT and INF_MAX_RT values apply only to the network
 interface on which the client received SOL_MAX_RT and/or INF_MAX_RT
 options.
8. DHCPv6 Server Behavior
 Sections 17.2.2 and 18.2 of RFC 3315 govern server operation in
 regard to option assignment. As a convenience to the reader, we
 mention here that the server will send options SOL_MAX_RT and
 INF_MAX_RT only if configured with specific values for them, and the
 client requested those options using the Option Request option.
 The DHCPv6 server MAY include the SOL_MAX_RT option in any response
 it sends to a client that has included the SOL_MAX_RT option code in
 an Option Request option. The SOL_MAX_RT option is sent in the main
 body of the message to client, not as an encapsulated option in,
 e.g., an IA_NA, IA_TA [RFC3315], or IA_PD [RFC3633] option.
 The DHCPv6 server MAY include the INF_MAX_RT option in any response
 it sends to a client that has included the INF_MAX_RT option code in
 an Option Request option. The INF_MAX_RT option is sent in the main
 body of the message to client, not as an encapsulated option in,
 e.g., an IA_NA, IA_TA, or IA_PD option.
9. DHCPv6 Relay Agent Behavior
 There are no additional requirements for relays.
10. Security Considerations
 This document introduces one security consideration beyond those
 described in RFC 3315. A malicious DHCPv6 server might cause a
 client to set its SOL_MAX_RT and INF_MAX_RT parameters to an
 unreasonably high value with the SOL_MAX_RT and INF_MAX_RT options,
 which may cause an undue delay in a client completing its DHCPv6
 protocol transaction in the case no other valid response is received.
 Assuming the client also receives a response from a valid DHCPv6
 server, large values for SOL_MAX_RT and INF_MAX_RT will not have any
 effect.
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RFC 7083 DHCPv6 SOL_MAX_RT Option November 2013
11. Acknowledgments
 Tomek Mrugalski edited the text for compliance with "Guidelines for
 Creating New DHCPv6 Options" [DHC-OPTION] and added important details
 to the Security Considerations section.
12. IANA Considerations
 IANA has assigned one option code each for OPTION_SOL_MAX_RT (82) and
 OPTION_INF_MAX_RT (83) from the "DHCP Option Codes" table of the
 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)" registry.
13. References
13.1. Normative References
 [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.
13.2. Informative References
 [DHC-OPTION]
 Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
 S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
 Work in Progress, September 2013.
 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
 Host Configuration Protocol (DHCP) version 6", RFC 3633,
 December 2003.
Author's Address
 Ralph Droms
 Cisco Systems
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 USA
 Phone: +1 978 936 1674
 EMail: rdroms@cisco.com
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