Network Working Group J. Abley
Internet-Draft ISC
Expires: September 11, 2005 March 10, 2005
Anycast Addressing in IPv6
draft-jabley-v6-anycast-clarify-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The IPv6 Addressing Architecture includes some restrictions on the
use of anycast addresses. These restrictions were intended to
protect the nascient IPv6 Internet from possible harmful consequences
that might result from widespread use of anycast as a mechanism to
distribute services.
Since then, anycast has been widely used to distribute services using
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IPv4, and production use of anycast in IPv6 also exists. While
anycast as a service distribution mechanism requires care, and is not
suitable for use in all situations, many useful applications of
anycast exist and the restrictions in the IPv6 Addressing
Architecture are no longer appropriate.
This document seeks to remove the restrictions on the use of anycast
addresses from the IPv6 Addressing Architecture.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. General Applicability of Anycast . . . . . . . . . . . . . . . 3
3. Analysis of IPv6 Anycast Restrictions . . . . . . . . . . . . 3
3.1 Anycast Source Addresses . . . . . . . . . . . . . . . . . 3
3.2 Anycast Addresses on Hosts . . . . . . . . . . . . . . . . 3
4. Anycast Addresses . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 4
Intellectual Property and Copyright Statements . . . . . . . . 5
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1. Introduction
The IPv6 Addressing Architecture [2] includes some restrictions on
the use of anycast addresses. These restrictions were intended to
protect the nascient IPv6 Internet from possible harmful consequences
that might result from widespread use of anycast as a mechanism to
distribute services.
This document seeks to remove the restrictions on the use of anycast
addresses from the IPv6 Addressing Architecture.
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 [1].
2. General Applicability of Anycast
Anycast has seen production deployment in distributing services over
both IPv4 and IPv6. However, anycast is not a suitable mechanism for
all protocols, nor all routing systems. A discussion of the design
considerations of an anycast service distribution strategy can be
found in [3].
3. Analysis of IPv6 Anycast Restrictions
3.1 Anycast Source Addresses
For many conventional services to be distributed using anycast, it is
necessary for reply datagrams sent from servers to clients to be
sourced from the same address that was used as the destination in
request datagrams sent from clients to servers. When such a service
is distributed using anycast, the destination address used in request
datagrams is necessarily an anycast address; corresponding reply
packets must therefore use the same anycast address as their source
address.
Being able to use an anycast address as the source address in an IPv6
datagram is a prerequisite for the distribution of many services
using anycast over IPv6.
3.2 Anycast Addresses on Hosts
Services are provided by hosts. For a service to be distributed
using anycast, datagrams directed at an anycast address must be
routed to hosts so that client requests can be processed. For such
datagrams to be received on hosts, it must be possible to assign
anycast addresses to interfaces on those hosts.
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Being able to apply an anycast address to an interface on a host is a
prerequisite for the distribution of services using anycast over
IPv6.
4. Anycast Addresses
Section 2.6 of RFC2373 [2] is updated as follows:
o An anycast address MAY be used as the source address of an IPv6
packet.
o An anycast address MAY be assigned to an IPv6 host.
5. IANA Considerations
This document requests no action from IANA.
6. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[3] Abley, J. and K. Lindqvist, "Operation of Anycast Services",
Internet-Draft draft-ietf-grow-anycast-00, February 2005.
Author's Address
Joe Abley
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
USA
Phone: +1 650 423 1317
Email: jabley@isc.org
URI: http://www.isc.org/
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Acknowledgment
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Internet Society.
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