DHCPv6 Prefix Length Hint Issues
draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-00

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DHC Working Group                                                 Y. Cui
Internet-Draft                                                     T. Li
Intended status: Informational                                    C. Liu
Expires: July 16, 2016                               Tsinghua University
                                                        January 13, 2016

                    DHCPv6 Prefix Length Hint Issues
           draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-00

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.

Status of This Memo

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   This Internet-Draft will expire on July 16, 2016.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   carefully, as they describe your rights and restrictions with respect

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

   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Description and Proposed Solutions  . . . . . . . . .   3
     2.1.  Creation of Solicit Message . . . . . . . . . . . . . . .   3
     2.2.  Receipt of Solicit message  . . . . . . . . . . . . . . .   4
     2.3.  Receipt of Advertise Message  . . . . . . . . . . . . . .   5
     2.4.  Creation of Renew/Rebind Message  . . . . . . . . . . . .   5
     2.5.  Receipt of Renew/Rebind Message . . . . . . . . . . . . .   6
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Contributors List . . . . . . . . . . . . . . . . . . . . . .   8
   6.  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 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.

   [RFC3633] 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 should be able to
   use the prefix-length hint to signal to the delegating router its
   real time need and it should be able to handle the prefixes which
   lengths are different from the prefix-length hint.  This document
   provides guidance on what a requesting router should do in different