DHCPv6 Prefix Length Hint Issues
draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-00
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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Internet-Draft DHCPv6 prefix-length hint Issues January 2016
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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
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