draft-ietf-v6ops-cidr-prefix-00.txt   draft-ietf-v6ops-cidr-prefix-01.txt 
v6ops Working Group M. Boucadair v6ops Working Group M. Boucadair
Internet-Draft France Telecom Internet-Draft France Telecom
Intended status: Best Current Practice A. Petrescu Intended status: Best Current Practice A. Petrescu
Expires: July 22, 2015 CEA, LIST Expires: August 17, 2015 CEA, LIST
F. Baker F. Baker
Cisco Systems Cisco Systems
January 18, 2015 February 13, 2015
IPv6 Prefix Length Recommendation for Forwarding IPv6 Prefix Length Recommendation for Forwarding
draft-ietf-v6ops-cidr-prefix-00 draft-ietf-v6ops-cidr-prefix-01
Abstract Abstract
IPv6 prefix length, as in IPv4, is a parameter conveyed and used in IPv6 prefix length, as in IPv4, is a parameter conveyed and used in
IPv6 routing and forwarding processes in accordance with the IPv6 routing and forwarding processes in accordance with the
Classless Inter-domain Routing (CIDR) architecture. The length of an Classless Inter-domain Routing (CIDR) architecture. The length of an
IPv6 prefix may be any number from zero to 128, although subnets IPv6 prefix may be any number from zero to 128, although subnets
using stateless address autoconfiguration (SLAAC) for address using stateless address autoconfiguration (SLAAC) for address
allocation conventionally use a /64 prefix. Hardware and software allocation conventionally use a /64 prefix. Hardware and software
algorithms should therefore impose no rules on prefix length, but algorithms should therefore impose no rules on prefix length, but
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 22, 2015. This Internet-Draft will expire on August 17, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Recommendation . . . . . . . . . . . . . . . . . . . . . . . 3 2. Recommendation . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
Discussions on the 64-bit boundary in IPv6 addressing ([RFC7421]) Discussions on the 64-bit boundary in IPv6 addressing ([RFC7421])
revealed a need for a clear recommendation on which bits must be used revealed a need for a clear recommendation on which bits must be used
by forwarding decision-making processes. by forwarding decision-making processes. However, such a
recommendation was out of scope for that document.
Although Section 2.5 of [RFC4291] states "IPv6 unicast addresses are Although Section 2.5 of [RFC4291] states "IPv6 unicast addresses are
aggregatable with prefixes of arbitrary bit-length, similar to IPv4 aggregatable with prefixes of arbitrary bit-length, similar to IPv4
addresses under Classless Inter-Domain Routing" (CIDR, [RFC4632]), addresses under Classless Inter-Domain Routing" (CIDR, [RFC4632]),
there is still a misinterpretation that IPv6 prefixes can be either there is still a misinterpretation that IPv6 prefixes can be either
/127 or any length up to /64. This (mis)interpretation is mainly /127 ([RFC6164]) or any length up to /64. This (mis)interpretation
induced by the 64-bit boundary in IPv6 addressing. is mainly induced by the 64-bit boundary in IPv6 addressing.
A detailed analysis of the 64-bit boundary in IPv6 addressing As discussed in [RFC7421], "the notion of a /64 boundary in the
together with the implication for end-site prefix assignment are address was introduced after the initial design of IPv6, following a
documented in [RFC7421], but no recommendation is included in that period when it was expected to be at /80". This evolution of the
document. IPv6 Addressing architecture, resulting in [RFC4291], and followed
with the addition of /127 prefixes for point-to-point links, clearly
demonstrates the intent for future IPv6 developments to have the
flexibility to change this part of the architecture when justified.
It is fundamental to not link routing and forwarding to the IPv6 It is fundamental to not link routing and forwarding to the IPv6
prefix/address semantics [RFC4291]. This document includes a prefix/address semantics [RFC4291]. This document includes a
recommendation for that aim. recommendation for that aim.
Forwarding decisions rely on the longest-match-first algorithm, which Forwarding decisions rely on the longest-match-first algorithm, which
stipulates that, given a choice between two prefixes in the stipulates that, given a choice between two prefixes in the
Forwarding Information Base (FIB) of different length that match the Forwarding Information Base (FIB) of different length that match the
destination address in each bit up to their respective lengths, the destination address in each bit up to their respective lengths, the
longer prefix is used. This document's recommendation is that IPv6 longer prefix is used. This document's recommendation (Section 2) is
forwarding must follow the longest-match-first rule, regardless of that IPv6 forwarding must follow the longest-match-first rule,
prefix length, barring the configuration of some overriding policy. regardless of prefix length, barring the configuration of some
overriding policy.
This recommendation does not conflict with the 64-bit boundary for
some IPv6 stateless address autoconfiguration (SLAAC, [RFC4862])
based schemes such as [RFC2464]. Indeed, [RFC7421] clarifies this is
only a parameter in the SLAAC process and other longer prefix lengths
are in operational use (e.g., either manually configured or based
upon DHCPv6 [RFC3315]).
A historical reminder of CIDR is documented in [RFC1380] and A historical reminder of CIDR is documented in [RFC1380] and
Section 2 of [RFC4632]. Section 2 of [RFC4632].
2. Recommendation 2. Recommendation
IPv6 MUST conform to the rules specified in Section 5.1 of [RFC4632]. IPv6 implementations MUST conform to the rules specified in
Section 5.1 of [RFC4632].
Forwarding decision-making processes MUST NOT restrict the length of Forwarding decision-making processes MUST NOT restrict the length of
IPv6 prefixes by design. In particular, forwarding processes MUST be IPv6 prefixes by design. In particular, forwarding processes MUST be
designed to process prefixes of any length up to /128, by increments designed to process prefixes of any length up to /128, by increments
of 1. of 1.
Obviously, policies can be enforced to restrict the length of IP Obviously, policies can be enforced to restrict the length of IP
prefixes advertised within a given domain or in a given prefixes advertised within a given domain or in a given
interconnection link. These policies are deployment-specific and/or interconnection link. These policies are deployment-specific and/or
driven by administrative (interconnection) considerations. driven by administrative (interconnection) considerations.
This recommendation does not conflict with the 64-bit boundary for
some IPv6 stateless address autoconfiguration (SLAAC, [RFC4862])
based schemes such as [RFC2464].
3. IANA Considerations 3. IANA Considerations
This document does not require any action from IANA. This document does not require any action from IANA.
4. Security Considerations 4. Security Considerations
This document does not introduce security issues in addition to what This document does not introduce security issues in addition to what
is discussed in [RFC4291]. is discussed in [RFC4291].
IPv6 security issues, including operational ones, are discussed in
[RFC4942] and [I-D.ietf-opsec-v6].
5. Acknowledgements 5. Acknowledgements
Thanks to Eric Vyncke, Christian Jacquenet, Brian Carpenter, Fernando Thanks to Eric Vyncke, Christian Jacquenet, Brian Carpenter, Fernando
Gont, Tatuya Jinmei, Lorenzo Colitti, and Ross Chandler for their Gont, Tatuya Jinmei, Lorenzo Colitti, Ross Chandler, and David Farmer
comments. for their contributions and comments.
Special thanks to Randy Bush for his support. Special thanks to Randy Bush for his support.
6. References 6. References
6.1. Normative References 6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, February 2006.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation (CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006. Plan", BCP 122, RFC 4632, August 2006.
6.2. Informative References 6.2. Informative References
[I-D.ietf-opsec-v6]
Chittimaneni, K., Kaeo, M., and E. Vyncke, "Operational
Security Considerations for IPv6 Networks", draft-ietf-
opsec-v6-05 (work in progress), October 2014.
[RFC1380] Gross, P. and P. Almquist, "IESG Deliberations on Routing [RFC1380] Gross, P. and P. Almquist, "IESG Deliberations on Routing
and Addressing", RFC 1380, November 1992. and Addressing", RFC 1380, November 1992.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998. Networks", RFC 2464, December 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. Address Autoconfiguration", RFC 4862, September 2007.
[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations", RFC 4942, 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.
[RFC7421] Carpenter, B., Chown, T., Gont, F., Jiang, S., Petrescu, [RFC7421] Carpenter, B., Chown, T., Gont, F., Jiang, S., Petrescu,
A., and A. Yourtchenko, "Analysis of the 64-bit Boundary A., and A. Yourtchenko, "Analysis of the 64-bit Boundary
in IPv6 Addressing", RFC 7421, January 2015. in IPv6 Addressing", RFC 7421, January 2015.
Authors' Addresses Authors' Addresses
Mohamed Boucadair Mohamed Boucadair
France Telecom France Telecom
Rennes 35000 Rennes 35000
France France
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