Network Working Group C. Huitema
Request for Comments: 3068 Microsoft
Category: Standards Track June 2001
An Anycast Prefix for 6to4 Relay Routers
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) The Internet Society (2001). All Rights Reserved.
This memo introduces a "6to4 anycast address" in order to simplify
the configuration of 6to4 routers. It also defines how this address
will be used by 6to4 relay routers, how the corresponding "6to4
anycast prefix" will be advertised in the IGP and in the EGP. The
memo documents the reservation by IANA (Internet Assigned Numbers
Authority) of the "6to4 relay anycast prefix."
According to [RFC3056], there are two deployment options for a 6to4
routing domain, depending on whether or not the domain is using an
IPv6 exterior routing protocol. If a routing protocol is used, then
the 6to4 routers acquire routes to all existing IPv6 networks through
the combination of EGP and IGP. If no IPv6 exterior routing protocol
is used, the 6to4 routers using a given relay router each have a
default IPv6 route pointing to the relay router. This second case is
typically used by small networks; for these networks, finding and
configuring the default route is in practice a significant hurdle.
In addition, even when the managers of these networks find an
available route, this route often points to a router on the other
side of the Internet, leading to very poor performance.
The operation of 6to4 routers requires either that the routers
participate in IPv6 inter-domain routing, or that the routers be
provisioned with a default route. This memo proposes a standard
method to define the default route. It introduces the IANA assigned
"6to4 Relay anycast prefix" from which 6to4 packets will be
Huitema Standards Track [Page 1]RFC 3068 An Anycast Prefix for 6to4 Relay Routers June 2001
automatically routed to the nearest available router. It allows the
managers of the 6to4 relay routers to control the sources authorized
to use their resource. It makes it easy to set up a large number of
6to4 relay routers, thus enabling scalability.
This memo uses the definitions introduced in [RFC3056], in particular
the definition of a 6to4 router and a 6to4 Relay Router. It adds the
definition of the 6to4 Relay anycast prefix, 6to4 Relay anycast
address, 6to4 IPv6 relay anycast address, and Equivalent IPv4 unicast
2.1 6to4 router (or 6to4 border router)
An IPv6 router supporting a 6to4 pseudo-interface. It is normally
the border router between an IPv6 site and a wide-area IPv4 network.
2.2 6to4 Relay Router
A 6to4 router configured to support transit routing between 6to4
addresses and native IPv6 addresses.
2.3 6to4 Relay anycast prefix
An IPv4 address prefix used to advertise an IPv4 route to an
available 6to4 Relay Router, as defined in this memo.
The value of this prefix is 18.104.22.168/24
2.4 6to4 Relay anycast address
An IPv4 address used to reach the nearest 6to4 Relay Router, as
defined in this memo.
The address corresponds to host number 1 in the 6to4 Relay anycast
2.5 6to4 IPv6 relay anycast address
The IPv6 address derived from the 6to4 Relay anycast address
according to the rules defined in 6to4, using a null prefix and a
null host identifier.
The value of the address is "2002:c058:6301::".
Huitema Standards Track [Page 2]RFC 3068 An Anycast Prefix for 6to4 Relay Routers June 20012.6 Equivalent IPv4 unicast address
A regular IPv4 address associated with a specific 6to4 Relay Router.
Packets sent to that address are treated by the 6to4 Relay Router as
if they had been sent to the 6to4 Relay anycast address.
3 Model, requirements
Operation of 6to4 routers in domains that don't run an IPv6 EGP
requires that these routers be configured with a default route to the
IPv6 Internet. This route will be expressed as a 6to4 address. The