DHCPv6 Prefix Length Hint Issues
draft-cui-dhc-dhcpv6-prefix-length-hint-issue-01

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Last updated 2015-10-11
Replaced by RFC 8168, RFC 8168
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DHC Working Group                                                 Y. Cui
Internet-Draft                                                     T. Li
Intended status: Standards Track                                  C. Liu
Expires: April 13, 2016                              Tsinghua University
                                                        October 11, 2015

                    DHCPv6 Prefix Length Hint Issues
            draft-cui-dhc-dhcpv6-prefix-length-hint-issue-01

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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Cui, et al.              Expires April 13, 2016                 [Page 1]
Internet-Draft      DHCPv6 prefix-length hint Issues        October 2015

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Description . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Creation of Solicit Message by the Client . . . . . . . .   3
     3.2.  Receipt of Solicit message by the Server  . . . . . . . .   3
     3.3.  Receipt of Advertise Message by the Client  . . . . . . .   4
     3.4.  Creation of Renew/Rebind Message by the Client  . . . . .   4
     3.5.  Receipt of Renew/Rebind Message by the Server . . . . . .   4
   4.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Creation of Solicit Message by the Client . . . . . . . .   5
     4.2.  Receipt of Solicit message by the Server  . . . . . . . .   5
     4.3.  Receipt of Advertise Message by the Client  . . . . . . .   6
     4.4.  Creation of Renew/Rebind Message by the Client  . . . . .   6
     4.5.  Receipt of Renew/Rebind Message by the Server . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Contributors List . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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, 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
   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 clients can't
   function normally 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.  The clients usually have higher preference on
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