DHCPv6 Prefix Length Hint Issues
draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-06

Document Type Active Internet-Draft (dhc WG)
Last updated 2017-03-31
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: October 2, 2017                             Tsinghua University
                                                          March 31, 2017

                    DHCPv6 Prefix Length Hint Issues
           draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-06

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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Internet-Draft      DHCPv6 prefix-length hint Issues          March 2017

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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
     3.6.  General Recommendation  . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   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 whose 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 an 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
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