DHCPv6 Prefix-Length Hint Issues
RFC 8168
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RFC - Proposed Standard
(May 2017; No errata)
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Last updated |
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2017-05-31
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Replaces |
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draft-cui-dhc-dhcpv6-prefix-length-hint-issue
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IETF
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plain text
pdf
html
bibtex
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Reviews |
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WG state
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Submitted to IESG for Publication
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Document shepherd |
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Bernie Volz
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Shepherd write-up |
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Show
(last changed 2016-10-28)
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| IESG |
IESG state |
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RFC 8168 (Proposed Standard)
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Consensus Boilerplate |
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Yes
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Telechat date |
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Responsible AD |
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Suresh Krishnan
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Send notices to |
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"Bernie Volz" <volz@cisco.com>
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| IANA |
IANA review state |
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Version Changed - Review Needed
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IANA action state |
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No IC
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Internet Engineering Task Force (IETF) T. Li
Request for Comments: 8168 C. Liu
Category: Standards Track Y. Cui
ISSN: 2070-1721 Tsinghua University
May 2017
DHCPv6 Prefix-Length Hint Issues
Abstract
DHCPv6 Prefix Delegation 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 it 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.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8168.
Copyright Notice
Copyright (c) 2017 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Li, et al. Standards Track [Page 1]
RFC 8168 DHCPv6 Prefix-Length Hint Issues May 2017
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. Normative References . . . . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
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. For example, 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 client; thus, it 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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