392 lines
14 KiB
Text
392 lines
14 KiB
Text
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Network Working Group R. Bush
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Internet-Draft Internet Initiative Japan
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Updates: 4291 (if approved) B. Carpenter
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Intended status: Standards Track Univ. of Auckland
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Expires: November 18, 2017 F. Gont
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SI6 Networks / UTN-FRH
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N. Hilliard
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INEX
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G. Huston
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APNIC
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C. Morrow
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GOOG
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J. Snijders
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NTT
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May 17, 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, none of which has withstood the test of time. The last
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remnant of IPv6 classful addressing is a rigid network interface
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identifier boundary at /64. This document removes the fixed position
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of that boundary for interface addressing.
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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 November 18, 2017.
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Bush, et al. Expires November 18, 2017 [Page 1]
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Internet-Draft IPv6 is Classless May 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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Table of Contents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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2. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . 3
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3. Identifier and Subnet Length Statements . . . . . . . . . . . 3
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4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4
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5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
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6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
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7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
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7.1. Normative References . . . . . . . . . . . . . . . . . . 5
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7.2. Informative References . . . . . . . . . . . . . . . . . 5
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
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Over the history of the IPv6 protocol, several classful addressing
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models have been proposed. The most notable example recommended Top-
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Level Aggregation (TLA) and Next-Level Aggregation (NLA) Identifiers
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[RFC2450], but was obsoleted by [RFC3587], leaving a single remnant
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of classful addressing in IPv6: a rigid network interface identifier
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boundary at /64. This document removes the fixed position of that
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boundary for interface addressing.
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Recent proposed changes to the IP Version 6 Addressing Architecture
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specification [RFC4291] have caused controversy. While link prefixes
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of varied lengths, e.g. /127, /126, /124, /120, ... /64 have been
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successfully deployed for many years, glaring mismatches between a
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formal specification and long-standing field deployment practices are
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never wise, not least because of the strong risk of mis-
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implementation, which can easily result in serious operational
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problems.
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Bush, et al. Expires November 18, 2017 [Page 2]
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Internet-Draft IPv6 is Classless May 2017
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This document also clarifies that IPv6 routing subnets may be of any
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length up to 128.
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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 assignment 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.ietf-6man-rfc4291bis] and RFC2464
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[I-D.hinden-6man-rfc2464bis], and the IETF recommendation for the
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generation of stable Interface Identifiers [RFC8064].
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[I-D.jinmei-6man-prefix-clarify] is also worth reading to clarify
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uses of varying prefix lengths on a single link.
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For host computers on local area networks, generation of interface
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identifiers is no longer necessarily bound to layer 2 addresses
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(MACs) [RFC7217] [RFC8064]. Therefore their length, previously fixed
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at 64 bits [RFC7136], is in fact a variably-sized parameter as
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explicitly acknowledged in Section 5.5.3(d) of [RFC4862] which
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states:
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Note that a future revision of the address architecture [RFC4291]
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and a future link-type-specific document, which will still be
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consistent with each other, could potentially allow for an
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interface identifier of length other than the value defined in the
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current documents. Thus, an implementation should not assume a
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particular constant. Rather, it should expect any lengths of
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interface identifiers.
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3. Identifier and Subnet Length Statements
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IPv6 unicast interfaces may use any subnet length up to 128 except
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for situations where an Internet Standard document may impose a
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particular length, for example Stateless Address Autoconfiguration
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(SLAAC) [RFC4862], or Using 127-Bit IPv6 Prefixes on Inter-Router
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Links [RFC6164].
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Additionally, this document clarifies that a node or router MUST
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support routing of any valid network prefix length, even if SLAAC or
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other standards are in use, because routing could choose to
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Bush, et al. Expires November 18, 2017 [Page 3]
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Internet-Draft IPv6 is Classless May 2017
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differentiate at a different granularity than is used by any such
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automated link local address configuration tools.
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4. Recommendations
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For historical reasons, when a prefix is needed on a link, barring
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other considerations, a /64 is recommended [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 SHOULD 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 was hard-coded, and to
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favor portability of devices and operating systems.
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Nonetheless, there is no reason in theory why an IPv6 node should not
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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 prefix length, with the value being a parameter
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per interface. For instance, the Interface Identifier length in the
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recommended (see [RFC8064]) algorithm for selecting stable interface
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identifiers [RFC7217] is a parameter, rather than a hardcoded value.
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5. Security Considerations
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Assuming 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]. For some specific subnets, such as point to
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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 forces an
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operational limit on such data structures, thus helping mitigate some
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pathological behaviors (such as Neighbor Cache Exhaustion attacks).
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6. IANA Considerations
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This document has no IANA Considerations.
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Bush, et al. Expires November 18, 2017 [Page 4]
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Internet-Draft IPv6 is Classless May 2017
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7. References
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7.1. Normative References
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[RFC2450] Hinden, R., "Proposed TLA and NLA Assignment Rules",
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RFC 2450, December 1998.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
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(IPv6) Specification", RFC 2460, December 1998.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
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Architecture", RFC 4291, February 2006.
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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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[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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7.2. Informative References
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[I-D.hinden-6man-rfc2464bis]
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Crawford, M. and R. Hinden, "Transmission of IPv6 Packets
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over Ethernet Networks", draft-hinden-6man-rfc2464bis-02
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(work in progress), March 2017.
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[I-D.ietf-6man-rfc4291bis]
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Hinden, R. and S. <>, "IP Version 6 Addressing
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Architecture", draft-ietf-6man-rfc4291bis-07 (work in
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progress), January 2017.
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[I-D.jinmei-6man-prefix-clarify]
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Jinmei, T., "Clarifications on On-link and Subnet IPv6
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Prefixes", draft-jinmei-6man-prefix-clarify-00 (work in
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progress), March 2017.
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[RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
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Unicast Address Format", RFC 3587, August 2003.
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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, August 2006.
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Bush, et al. Expires November 18, 2017 [Page 5]
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Internet-Draft IPv6 is Classless May 2017
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
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Address Autoconfiguration", RFC 4862, September 2007.
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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, April 2011.
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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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Authors' Addresses
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Randy Bush
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Internet Initiative Japan
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5147 Crystal Springs
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Bainbridge Island, Washington 98110
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US
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Email: randy@psg.com
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Brian Carpenter
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Department of Computer Science
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University of Auckland
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PB 92019
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Auckland 1142
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New Zealand
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Email: brian.e.carpenter@gmail.com
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Bush, et al. Expires November 18, 2017 [Page 6]
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Internet-Draft IPv6 is Classless May 2017
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Fernando Gont
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SI6 Networks / UTN-FRH
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Evaristo Carriego 2644
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Haedo, Provincia de Buenos Aires 1706
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Argentina
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Phone: +54 11 4650 8472
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Email: fgont@si6networks.com
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URI: http://www.si6networks.com
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Nick Hilliard
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INEX
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4027 Kingswood Road
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Dublin 24
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Ireland
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Email: nick@inex.ie
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Geoff Huston
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Email: gih@apnic.net
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Chris Morrow
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Google, Inc.
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1600 Ampitheatre Parkway
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Mountain View, California
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United States of America
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Email: morrowc@google.com
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Job Snijders
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NTT Communications
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Theodorus Majofskistraat 100
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Amsterdam 1065 SZ
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The Netherlands
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Email: job@ntt.net
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Bush, et al. Expires November 18, 2017 [Page 7]
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