Network Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track November 6, 2007
Expires: May 9, 2008
Reserved IPv6 Interface Identifiers
draft-krishnan-ipv6-reserved-iids-02
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Copyright (C) The IETF Trust (2007).
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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.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Issues with reusing reserved Interface Identifiers . . . . . . 5
3.1. Possible solutions . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. 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].
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2. Introduction
An IPv6 unicast address is composed of two parts. A subnet prefix
and an interface identifier (IID) that identifies an unique interface
within the subnet prefix. The structure of an IPv6 unicast address
is depicted in the 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 binary value
000, Interface identifiers are required to be 64 bits long (i.e.
n==64) . If the interface identifiers are generated from an unique
token like an ethernet MAC address, they need to set bit 6 of the
first octet to one. If they are not generated from an unique token
they need to set bit 6 to zero. Examples of mechanisms that generate
interface identifiers without an unique token include
Cryptographically Generated Addresses [RFC3972], Privacy Addresses
[PRIVACY], Hash Based Addresses [HBA] etc. Non-unique interface
identifiers can also be allocated using managed address assignment
mechanisms like DHCPv6 [RFC3315].
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3. 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 [PRIVACY] comes up with an IID of fdff:
ffff:ffff:fffe . This node will receive requests from all nodes that
are requesting a service from a MobileIPv6 home agent. At best this
is an annoyance to the node that came up with this address. In the
worst case scenario 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
auto-configuration or for managed address configuration.
3.1. Possible solutions
There are two possible ways to go about avoiding usage of these
reserved interface identifiers. One of them would be to add
normative reference to each specification that reserves an interface
identifier. The other one 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. This is because the number of such specifications can 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. e.g.
Reserving certain identifiers may be useful in certain protocols such
as PMIP in order to avoid duplicate address detection on point to
point links, but PMIP will be at a lower standardization level than
the address sutoconfiguration standards and hence not referable from
them.
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4. IANA Considerations
This document requests the creation of an IANA registry for reserved
IPv6 Interface Identifiers. Initial values for the reserved IPv6
Interface Identifiers are given below.
+-----------------------------------------+-------------------------+
| Interface Identifier Range | Description |
+-----------------------------------------+-------------------------+
| 0000:0000:0000:0000-0000:0000:0000:0000 | Subnet Router Anycast |
| | [RFC4291] |
| | |
| fdff:ffff:ffff:ff80-fdff:ffff:ffff:fffd | Reserved Subnet Anycast |
| | [RFC2526] |
| | |
| fdff:ffff:ffff:fffe-fdff:ffff:ffff:fffe | MobileIPv6 Home Agents |
| | Anycast [RFC2526] |
| | |
| fdff:ffff:ffff:ffff-fdff:ffff:ffff:ffff | Reserved Subnet Anycast |
| | [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 but in exceptional
circumstances are to be made through Standards Action [IANABIS].
Assignments consist of a single interface identifier or a range of
interface identifiers.
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5. 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 and Tim Enos for
reviewing this document and suggesting changes.
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6. Security Considerations
Information that creates or updates a registration needs to be
authenticated and authorized. By utilizing one of the reserved
interface identifiers an IPv6 node might receive requests that it is
not authorized to receive.
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7. References
7.1. 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.
7.2. Informative References
[HBA] Bagnulo, M., "Hash Based Addresses (HBA)",
draft-ietf-shim6-hba-02 (work in progress), October 2006.
[IANABIS] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs",
draft-narten-iana-considerations-rfc2434bis-05 (work in
progress), September 2006.
[PRIVACY] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", draft-ietf-ipv6-privacy-addrs-v2-05 (work in
progress), October 2006.
[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.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
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Author's Address
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
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