





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
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   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.







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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.





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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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