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Network Working Group N. Bourbaki
Internet-Draft The Intertubes
Intended status: Standards Track April 17, 2017
Expires: October 19, 2017
IPv6 is Classless
draft-bourbaki-6man-classless-ipv6-00
Abstract
Over the history of IPv6, various classful address models have been
proposed, particularly Top-Level Aggregation (TLA) and Next-Level
Aggregation(NLA) Identifiers. They have all proved to be mistakes.
The last remnant is a rigid boundary at /64. This document removes
that rigidity as far as routing is concerned.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 19, 2017.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . 2
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. A simple Statement . . . . . . . . . . . . . . . . . . . . . 3
5. Notes and Recommendations . . . . . . . . . . . . . . . . . . 3
6. Security Considerations . . . . . . . . . . . . . . . . . . . 3
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
10.1. Normative References . . . . . . . . . . . . . . . . . . 4
10.2. Informative References . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Over the history of IPv6, various classful address models have been
proposed, particularly Top-Level Aggregation (TLA) and Next-Level
Aggregation(NLA) Identifiers. They have all proved to be mistakes.
For example, TLA and NLA were obsoleted by [RFC3587]. The last
remnant is a rigid boundary at /64. This document removes that
rigidity as far as routing is concerned.
2. Suggested Reading
It is assumed that the reader understands the history of classful
addressing in IPv4 and why it was abolished [RFC4632]. Of course,
the acute need to conserve address space that forced the adoption of
classless addressing for IPv4 does not apply to IPv6; but the
arguments for operational flexibility in address allocation remain
compelling.
It is also assumed that the reader understands IPv6, [RFC2460], IP
Version 6 Addressing Architecture, see [RFC4291], and the proposed
changes to [RFC4291], see [I-D.hinden-6man-rfc2464bis].
NOTE: do we mean 4291bis (currently moribund) or 2464bis?
An important recent development in IPv6 is that for host computers on
local area networks, the way in which interface identifiers are
formed is no longer bound to layer 2 addresses (MAC addresses)
[RFC7217]. We can therefore appreciate that their length, previously
fixed at 64 bits [RFC7136], is in fact a free parameter as stated in
[RFC4862].
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3. Background
Some confusion has been caused by the IP Version 6 Addressing
Architecture, [RFC4291], and the proposed changes in
[I-D.hinden-6man-rfc2464bis] with respect to allowed maximum prefix
lengths and the minimum host part (sometimes known as interface
identifier) on a link.
Meanwhile, link prefixes of varied lengths, /127, /126, /124, /120,
... /64 have been successfully deployed for many years. Having the
formal specification be unclear risks potential mis-implementation by
the naive, which could result in operational disasters.
4. A simple Statement
To state it simply, IPv6 unicast routing is based on prefixes of any
valid length up to 128 except for links where an Internet Standard
such as, for example, Stateless Address AutoConfiguration [RFC4862],
or Using 127-Bit IPv6 Prefixes on Inter-Router Links [RFC6164] is in
use.
5. Notes and Recommendations
For historical reasons, when a prefix is needed on a link, barring
other considerations, a /64 is traditional [RFC7136].
The length of the prefix identifier in Stateless Address
AutoConfiguration, [RFC4862] is a parameter; its length needs to be
sufficient for effective randomization for privacy reasons. For
example, a /48 might be sufficient. But operationally we recommend,
barring strong considerations to the contrary, using 64-bits for
SLAAC in order not to discover bugs where 64-bits was hard-coded, and
to favor portability of devices and operating systems.
None the less, there is no reason in theory why an IPv6 node should
not operate with different interface identfier lengths on different
physical interfaces. Thus a correct implementation of SLAAC must in
fact allow for any length of prefix, with the value being
parameterised per interface.
NOTE: should we comment on the fact that at least Linux and Windows
seem to assume that the default prefix is /64 in the management CLI?
6. Security Considerations
This document has no known security impact, assuming that user
devices use an unpredictable interface identifier [RFC7721] for
privacy.
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7. IANA Considerations
This document has no IANA Considerations.
8. Authors
The original draft was by Randy Bush, who was immediately aided and
abetted by Brian Carpenter, Job Snijders, [ your name here ].
9. Acknowledgments
The authors wish to thank .
10. References
10.1. Normative References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
10.2. Informative References
[I-D.hinden-6man-rfc2464bis]
Crawford, M. and R. Hinden, "Transmission of IPv6 Packets
over Ethernet Networks", draft-hinden-6man-rfc2464bis-02
(work in progress), March 2017.
[RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
Unicast Address Format", RFC 3587, August 2003.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
Router Links", RFC 6164, April 2011.
[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
February 2014, <http://www.rfc-editor.org/info/rfc7136>.
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[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<http://www.rfc-editor.org/info/rfc7721>.
Author's Address
Nicolas Bourbaki
The Intertubes
42 Rue du Jour
Sophia-Antipolis ::1
FR
Email: bourbaki@bogus.com
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