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.
Copyright (c) 2009 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
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Please review these documents carefully, as they describe your rights
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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.
Krishnan Standards Track [Page 1]RFC 5453 Reserved IPv6 Interface Identifiers February 2009Table of Contents
1. Introduction ....................................................2
1.1. Applicability ..............................................2
1.2. Requirements Notation ......................................3
2. Issues with Reusing Reserved Interface Identifiers ..............3
2.1. Possible Solutions .........................................3
3. IANA Considerations .............................................3
4. Acknowledgements ................................................4
5. Security Considerations .........................................4
6. References ......................................................5
6.1. Normative References .......................................5
6.2. Informative References .....................................5
Appendix A. List of Potentially Affected RFCs ......................6
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].
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.
Krishnan Standards Track [Page 2]RFC 5453 Reserved IPv6 Interface Identifiers February 20091.2. 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].
2. 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.
2.1. 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.
3. IANA Considerations
This document creates an IANA registry for reserved IPv6 interface
identifiers. Initial values for the reserved IPv6 interface
identifiers are given below.
Krishnan Standards Track [Page 3]RFC 5453 Reserved IPv6 Interface Identifiers February 2009
| Interface Identifier Range | Description |
| 0000:0000:0000:0000 | Subnet-Router Anycast |
| | [RFC4291] |
| | |
| FDFF:FFFF:FFFF:FF80-FDFF:FFFF:FFFF:FFFF | Reserved Subnet Anycast |
| | Addresses[RFC2526] |
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
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.
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.
5. 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].
Krishnan Standards Track [Page 4]RFC 5453 Reserved IPv6 Interface Identifiers February 20096. References6.1. 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,
6.2. 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,
Krishnan Standards Track [Page 5]RFC 5453 Reserved IPv6 Interface Identifiers February 2009Appendix 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
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
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
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Krishnan Standards Track [Page 6]