RFC5453

Network Working Group S. Krishnan Request for Comments: 5453 Ericsson Category: Standards Track February 2009

              Reserved IPv6 Interface Identifiers

Status of This Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

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Abstract

Interface identifiers in IPv6 unicast addresses are used to identify interfaces on a link. They are required to be unique within a subnet. Several RFCs have specified interface identifiers or identifier ranges that have a special meaning attached to them. An IPv6 node autoconfiguring an interface identifier in these ranges will encounter unexpected consequences. Since there is no centralized repository for such reserved identifiers, this document aims to create one.

Introduction

An IPv6 unicast address is composed of two parts: a subnet prefix and an interface identifier (IID) that identifies a unique interface within the subnet prefix. The structure of an IPv6 unicast address is depicted in "IPv6 Addressing Architecture" RFC4291 and is replicated here for clarity.

| n bits | 128-n bits | +-------------------------------+---------------------------------+ | subnet prefix | interface ID | +-------------------------------+---------------------------------+

               Figure 1: IPv6 Unicast Address Format

For all unicast addresses, except those that start with the binary value 000, Interface IDs are required to be 64 bits long and to be constructed in Modified EUI-64 format RFC4291. Examples of mechanisms that generate interface identifiers without a unique token include Cryptographically Generated Addresses RFC3972, Privacy Addresses RFC4941, Hash-Based Addresses [HBA], etc. Non-unique interface identifiers can also be allocated using managed address assignment mechanisms like DHCPv6 (Dynamic Host Configuration Protocol for IPv6) RFC3315.

Applicability

This document applies only to interface identifiers that are formed in the modified EUI-64 format as defined in Appendix A of RFC4291. All other types of interface identifiers are out of its scope.

Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.

Issues with Reusing Reserved Interface Identifiers

Let us assume a node comes up with an interface identifier that has been reserved for use in some other capacity, e.g., an IPv6 node that uses temporary IPv6 addresses RFC4941 comes up with an IID of fdff:ffff:ffff:ffff. This node will receive requests from all nodes that are requesting a service from a Mobile IPv6 home agent since the above-mentioned interface identifier has been reserved in RFC2526 to serve as a MIPv6 home agent's anycast address. At best, this is an annoyance to the node that came up with this address. At worst, another node on the link would be denied service and may not look for other methods of acquiring a home agent. Thus, such reserved interface identifiers MUST NOT be used for autonomous autoconfiguration or for managed address configuration.

Possible Solutions

There are two possible ways to go about avoiding usage of these reserved interface identifiers. One of them would be to add a normative reference to each specification that reserves an interface identifier. The other would be to create an IANA registry for such interface identifiers. There are two disadvantages to the normative reference approach. Firstly, this approach does not scale well because the number of such specifications that would need to be updated is large. Secondly, the maturity level of the document reserving the IID might be lower than the one prohibited from using it; this will cause a downward reference problem. Therefore, the better solution is to create an IANA registry for this purpose.

IANA Considerations

This document creates an IANA registry for reserved IPv6 interface identifiers. Initial values for the reserved IPv6 interface identifiers are given below.

+-----------------------------------------+-------------------------+ | Interface Identifier Range | Description | +-----------------------------------------+-------------------------+ | 0000:0000:0000:0000 | Subnet-Router Anycast | | | RFC4291 | | | | | FDFF:FFFF:FFFF:FF80-FDFF:FFFF:FFFF:FFFF | Reserved Subnet Anycast | | | AddressesRFC2526 | +-----------------------------------------+-------------------------+

                   Table 1: Current Assignments

It is possible that implementations might predate a specific assignment from this registry and hence not be cognizant of the reserved nature of the interface identifier. Hence, future assignments from this registry are discouraged. Future assignments, if any, are to be made through Standards Action RFC5226. Assignments consist of a single interface identifier or a range of interface identifiers.

NOTE: The address :: (all zeros in the interface identifier field) is used as the unspecified address and ::/0 is used as a default route indicator, as specified in RFC5156. These uses do not conflict with the reserved interface identifiers defined here, since the reserved identifiers defined in this document are used for avoiding conflicts with stateless address autoconfiguration that utilizes a 64-bit prefix length.

Acknowledgements

The author would like to thank Alain Durand, Alex Petrescu, Bernie Volz, Bob Hinden, Christian Huitema, Fred Templin, Jordi Palet Martinez, Pekka Savola, Remi Denis-Courmount, Tim Enos, Ed Jankiewicz, Brian Carpenter, Alfred Hoenes, Jari Arkko, Pasi Eronen, Tim Polk, Lars Eggert, Derek Atkins, and Robert Sparks for reviewing this document and suggesting changes.

Security Considerations

By utilizing one of the reserved interface identifiers, an IPv6 node might receive requests that it is not authorized to receive. Information that creates or updates a registration in this registry needs to be authenticated and authorized by the IANA based on the instructions set forth by RFC5226.

References

Normative References

RFC2119 Bradner, S., "Key words for use in RFCs to Indicate

          Requirement Levels", BCP 14, RFC 2119, March 1997.

RFC2526 Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast

          Addresses", RFC 2526, March 1999.

RFC4291 Hinden, R. and S. Deering, "IP Version 6 Addressing

          Architecture", RFC 4291, February 2006.

RFC5226 Narten, T. and H. Alvestrand, "Guidelines for Writing an

          IANA Considerations Section in RFCs", BCP 26, RFC 5226,
          May 2008.

Informative References

[HBA] Bagnulo, M., "Hash Based Addresses (HBA)", Work in

          Progress, October 2006.

RFC3315 Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,

          C., and M. Carney, "Dynamic Host Configuration Protocol
          for IPv6 (DHCPv6)", RFC 3315, July 2003.

RFC3972 Aura, T., "Cryptographically Generated Addresses (CGA)",

          RFC 3972, March 2005.

RFC4941 Narten, T., Draves, R., and S. Krishnan, "Privacy

          Extensions for Stateless Address Autoconfiguration in
          IPv6", RFC 4941, September 2007.

RFC5156 Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,

          April 2008.

Appendix A. List of Potentially Affected RFCs

Implementations of the following RFCs need to be aware of the reserved interface identifier ranges when they allocate new addresses. Future revisions of these RFCs should ensure that this is either already sufficiently clear or that the text is amended to take this into account.

o RFC 2590 - Transmission of IPv6 Packets over Frame Relay Networks

  Specification

o RFC 3315 - Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

o RFC 3972 - Cryptographically Generated Addresses (CGA)

o RFC 4489 - A Method for Generating Link-Scoped IPv6 Multicast

  Addresses

o RFC 4862 - IPv6 Stateless Address Autoconfiguration

o RFC 4941 - Privacy Extensions for Stateless Address

  Autoconfiguration in IPv6

o RFC 4982 - Support for Multiple Hash Algorithms in

  Cryptographically Generated Addresses (CGAs)

o RFC 5072 - IP Version 6 over PPP

Author's Address

Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada

Phone: +1 514 345 7900 x42871 EMail: [email protected]