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

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Document Type Active Internet-Draft (dhc WG)
Last updated 2016-06-22 (latest revision 2016-06-19)
Replaces draft-cui-dhc-dhcpv6-prefix-length-hint-issue
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DHC Working Group                                                 Y. Cui
Internet-Draft                                                     T. Li
Intended status: Standards Track                                  C. Liu
Expires: December 21, 2016                           Tsinghua University
                                                           June 19, 2016

                    DHCPv6 Prefix Length Hint Issues
           draft-ietf-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 December 21, 2016               [Page 1]
Internet-Draft      DHCPv6 prefix-length hint Issues           June 2016

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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  . . . . . . . . . . . .   5
     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(OPTION_IAPREFIX), 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
   prefix-length hint values depending on server policy.  However, some
   requesting routers may not be able to function (or only in a degraded
   state) 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.  For other hints,
   such as requesting for a explicit address or lifetime, this might be
   less critical as it just help a client that wishes to continue using
   what it used last time, or a client that wants to Renew its lease for
   a certain period of time.  The prefix-length hint directly impacts
   the operational capability of the requesting router, thus should be
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