336 lines
11 KiB
Text
336 lines
11 KiB
Text
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Network Working Group N. Bourbaki
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Internet-Draft The Intertubes
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Intended status: Standards Track April 2017
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Expires: October 3, 2017
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IPv6 is Classless
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draft-bourbaki-6man-classless-ipv6-00
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Abstract
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Over the history of IPv6, various classful address models have been
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proposed, particularly Top-Level Aggregation (TLA) and Next-Level
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Aggregation (NLA) Identifiers. They have all proved to be mistakes.
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The last remnant is a rigid boundary at /64. This document removes
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that rigidity as far as routing is concerned.
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Status of This Memo
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This Internet-Draft is submitted in full conformance with the
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provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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Task Force (IETF). Note that other groups may also distribute
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working documents as Internet-Drafts. The list of current Internet-
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Drafts is at http://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on October 3, 2017.
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Copyright Notice
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Copyright (c) 2017 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
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Bourbaki Expires October 3, 2017 [Page 1]
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Internet-Draft IPv6 is Classless April 2017
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Table of Contents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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2. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . 2
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3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
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4. A simple Statement . . . . . . . . . . . . . . . . . . . . . 3
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5. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
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6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
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7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
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8. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
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9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
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10.1. Normative References . . . . . . . . . . . . . . . . . . 4
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10.2. Informative References . . . . . . . . . . . . . . . . . 5
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
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Over the history of IPv6, various classful address models have been
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proposed, particularly Top-Level Aggregation (TLA) and Next-Level
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Aggregation(NLA) Identifiers. They have all proved to be mistakes.
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For example, TLA and NLA were obsoleted by [RFC3587]. The last
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remnant is a rigid boundary at /64. This document removes that
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rigidity as far as routing is concerned.
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2. Suggested Reading
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It is assumed that the reader understands the history of classful
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addressing in IPv4 and why it was abolished [RFC4632]. Of course,
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the acute need to conserve address space that forced the adoption of
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classless addressing for IPv4 does not apply to IPv6; but the
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arguments for operational flexibility in address allocation remain
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compelling.
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It is also assumed that the reader understands IPv6 [RFC2460], the IP
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Version 6 Addressing Architecture [RFC4291], the proposed changes to
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RFC4291 [I-D.hinden-6man-rfc4291bis], and the recent recommendations
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for the generation of stable Interface Identifiers [RFC8064].
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An important recent development in IPv6 is that for host computers on
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local area networks, the way in which interface identifiers are
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formed is no longer bound to layer 2 addresses (MAC addresses)
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[RFC7217] [RFC8064]. We can therefore appreciate that their length,
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previously fixed at 64 bits [RFC7136], is in fact a free parameter as
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stated in [RFC4862].
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Bourbaki Expires October 3, 2017 [Page 2]
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Internet-Draft IPv6 is Classless April 2017
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3. Background
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Some confusion has been caused by the IP Version 6 Addressing
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Architecture, [RFC4291], and the proposed changes in
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[I-D.hinden-6man-rfc4291bis] with respect to the minimum subnet size.
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Meanwhile, link prefixes of varied lengths, /127, /126, /124, /120,
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... /64 have been successfully deployed for many years. Having the
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formal specification be unclear risks potential mis-implementation by
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the naive, which could result in operational disasters.
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4. A simple Statement
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To state it simply, IPv6 unicast routing is based on prefixes of any
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valid length up to 128 except for links where an Internet Standard
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such as, for example, Stateless Address AutoConfiguration [RFC4862],
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or Using 127-Bit IPv6 Prefixes on Inter-Router Links [RFC6164] is in
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use.
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5. Recommendations
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For backwards compatibility, when a prefix is needed on a link,
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barring other considerations, a /64 is RECOMENDED [RFC7136].
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The length of the Interface Identifier in Stateless Address
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AutoConfiguration [RFC4862] is a parameter; its length needs to be
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sufficient for effective randomization for privacy reasons. For
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example, a /48 might be sufficient. But operationally we RECOMMEND,
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barring strong considerations to the contrary, using 64-bits for
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SLAAC in order not to discover bugs where 64-bits was hard-coded, and
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to favor portability of devices and operating systems.
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None the less, there is no reason in theory why an IPv6 node should
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not operate with different interface identfier lengths on different
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physical interfaces. Thus a correct implementation of SLAAC must in
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fact allow for any length of prefix, with the value being
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parameterised per interface. For instance, the Interface Identifier
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length in the recommended (see [RFC8064]) algorithm for selecting
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stable interface identifiers [RFC7217] is a parameter, rather than a
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hardcoded value.
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NOTE: should we comment on the fact that at least Linux and Windows
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seem to assume that the default prefix is /64 in the management CLI?
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Bourbaki Expires October 3, 2017 [Page 3]
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Internet-Draft IPv6 is Classless April 2017
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6. Security Considerations
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Assumming that nodes employ unpredictable interface identifiers
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[RFC7721], the subnet size may have an impact on some security and
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privacy properties of a network. Namely, the smaller the subnet
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size, the more feasible it becomes to perform IPv6 address scans
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[RFC7707] [RFC7721]. However, that for some specific subnets (such
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as point to point links), this may be less of an issue.
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On the other hand, we assume that a number of IPv6 implementations
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fail to enforce limits on the size of some of the data structures
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they employ for communicating with neighboring nodes, such as the
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Neighbor Cache. In such cases, the use of smaller subnets
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essentially enforces an operational limit on such data structures,
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thus helping mitigate some pathological behaviors (such as Neighbor
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Cache Exhaustion attacks).
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7. IANA Considerations
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This document has no IANA Considerations.
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8. Authors
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The original draft was by Randy Bush, who was immediately aided and
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abetted by Brian Carpenter, Chris Morrow, Job Snijders, [ your name
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here ].
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9. Acknowledgments
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The authors wish to thank .
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10. References
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10.1. Normative References
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
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(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
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December 1998, <http://www.rfc-editor.org/info/rfc2460>.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
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Architecture", RFC 4291, DOI 10.17487/RFC4291, February
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2006, <http://www.rfc-editor.org/info/rfc4291>.
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[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
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Interface Identifiers with IPv6 Stateless Address
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Autoconfiguration (SLAAC)", RFC 7217,
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DOI 10.17487/RFC7217, April 2014,
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<http://www.rfc-editor.org/info/rfc7217>.
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Bourbaki Expires October 3, 2017 [Page 4]
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Internet-Draft IPv6 is Classless April 2017
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[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
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"Recommendation on Stable IPv6 Interface Identifiers",
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RFC 8064, DOI 10.17487/RFC8064, February 2017,
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<http://www.rfc-editor.org/info/rfc8064>.
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10.2. Informative References
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[I-D.hinden-6man-rfc4291bis]
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Hinden, B. and S. Deering, "IP Version 6 Addressing
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Architecture", draft-hinden-6man-rfc4291bis-06 (work in
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progress), October 2015.
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[RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
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Unicast Address Format", RFC 3587, DOI 10.17487/RFC3587,
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August 2003, <http://www.rfc-editor.org/info/rfc3587>.
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[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
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(CIDR): The Internet Address Assignment and Aggregation
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Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
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2006, <http://www.rfc-editor.org/info/rfc4632>.
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
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Address Autoconfiguration", RFC 4862,
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DOI 10.17487/RFC4862, September 2007,
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<http://www.rfc-editor.org/info/rfc4862>.
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[RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
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L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
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Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011,
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<http://www.rfc-editor.org/info/rfc6164>.
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[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
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Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
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February 2014, <http://www.rfc-editor.org/info/rfc7136>.
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[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
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Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
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<http://www.rfc-editor.org/info/rfc7707>.
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[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
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Considerations for IPv6 Address Generation Mechanisms",
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RFC 7721, DOI 10.17487/RFC7721, March 2016,
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<http://www.rfc-editor.org/info/rfc7721>.
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Bourbaki Expires October 3, 2017 [Page 5]
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Internet-Draft IPv6 is Classless April 2017
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Author's Address
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Nicolas Bourbaki
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The Intertubes
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42 Rue du Jour
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Sophia-Antipolis ::1
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FR
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Email: bourbaki@bogus.com
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Bourbaki Expires October 3, 2017 [Page 6]
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