DHCPv6 Prefix Length Hint Issues
draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-03

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Document Type Active Internet-Draft (dhc WG)
Last updated 2016-10-14 (latest revision 2016-07-26)
Replaces draft-cui-dhc-dhcpv6-prefix-length-hint-issue
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DHC Working Group                                                  T. Li
Internet-Draft                                                    C. Liu
Intended status: Standards Track                                  Y. Cui
Expires: January 27, 2017                            Tsinghua University
                                                           July 26, 2016

                    DHCPv6 Prefix Length Hint Issues
           draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-03

Abstract

   DHCPv6 Prefix Delegation [RFC3633] allows a client 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 client and server 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 client and server could do in different situations.

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Li, et al.              Expires January 27, 2017                [Page 1]
Internet-Draft      DHCPv6 prefix-length hint Issues           July 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
     3.6.  General Recommendation  . . . . . . . . . . . . . . . . .   8
   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 client to include a
   prefix-length hint value in the message sent to the server, to
   indicate a preference for the size of the prefix to be delegated.  A
   prefix-length hint is communicated by a client to the server by
   including an IA_PD Prefix Option(IAPREFIX 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 servers are free
   to ignore the prefix-length hint values depending on server policy.
   However, some clients 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 client is asking
   for a /56 and the server returns a /64, the functionality of the
   client 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, this might be less critical as it just helps
   a client that wishes to continue using what it used last time.  The
   prefix-length hint directly impacts the operational capability of the
   client, thus should be given more consideration.

   [RFC3633] is unclear about how the client and server should act in
   different situations involving the prefix-length hint.  From the
   client perspective, it should be able to use the prefix-length hint
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