DHCPv6 Prefix Length Hint Issues
draft-cui-dhc-dhcpv6-prefix-length-hint-issue-02

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Last updated 2015-11-13
Replaced by RFC 8168, RFC 8168
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DHC Working Group                                                 Y. Cui
Internet-Draft                                                     T. Li
Intended status: Informational                                    C. Liu
Expires: May 16, 2016                                Tsinghua University
                                                       November 13, 2015

                    DHCPv6 Prefix Length Hint Issues
            draft-cui-dhc-dhcpv6-prefix-length-hint-issue-02

Abstract

   DHCPv6 Prefix Delegation [RFC3633] allows a requesting router to
   include a prefix-length hint value in the IA_PD option to indicate a
   preference for the size of the prefix to be delegated, but is unclear
   about how the requesting router and delegating router should act in
   different situations involving the prefix-length hint.  This document
   provides a summary of the existing problems with the prefix-length
   hint and guidance on what the requesting router and delegating router
   could do in different situations.

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Cui, et al.               Expires May 16, 2016                  [Page 1]
Internet-Draft      DHCPv6 prefix-length hint Issues       November 2015

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Description and Proposed Solutions  . . . . . . . . .   3
     3.1.  Creation of Solicit Message . . . . . . . . . . . . . . .   3
     3.2.  Receipt of Solicit message  . . . . . . . . . . . . . . .   4
     3.3.  Receipt of Advertise Message  . . . . . . . . . . . . . .   5
     3.4.  Creation of Renew/Rebind Message  . . . . . . . . . . . .   6
     3.5.  Receipt of Renew/Rebind Message . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Contributors List . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   DHCPv6 Prefix Delegation [RFC3633] allows a requesting router to
   include a prefix-length hint value in the message sent to the
   delegating router, to indicate a preference for the size of the
   prefix to be delegated.  A prefix-length hint is communicated by a
   requesting router to the delegating router by including an IA_PD
   Prefix Option, encapsulated in an IA_PD option, with the "IPv6
   prefix" field set to zero and the "prefix-length" field set to a non-
   zero value.  The delegating routers are free to ignore the hint
   values depending on server policy.  This would not cause problems for
   some hint values such as T1 and T2 lifetimes, but it would be an
   issue for the prefix-length hint.  Some requesting routers can't
   function normally when they're provided with a prefix which length is
   different from what they requested.  E.g. if the requesting router is
   asking for a /56 and the delegating router returns a /64, the
   functionality of the requesting router might be limited because it
   might not be able to split the prefix for all its interfaces.  The
   requesting routers usually have higher preference on the prefix-
   length hint than the other option hints, and it should be given more
   consideration.

   The current specification is unclear about how the requesting router
   and delegating router should act in different situations involving
   the prefix-length hint.  From the requesting router perspective, it
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