Anycast BOF

Steve Deering <> Fri, 29 October 1999 15:30 UTC

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Date: Fri, 29 Oct 1999 08:28:29 -0700
From: Steve Deering <>
Subject: Anycast BOF
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At the request of the IAB, and with the blessing of the Internet Area
Directors, there will be a BOF on the topic of IP anycast addressing at
the upcoming IETF meeting in Washington.  The BOF is currently scheduled
for 1930-2200 on Monday evening, Nov. 8.  Here's a description of the
purpose and topics of the BOF:

                       Anycast BOF Description

An anycast IP address [RFC 1546] is an address assigned to a set of nodes,
such that a packet sent to that address is delivered to one member of the
set, in particular to the member "nearest" the sender according to the
routing system's measure of distance.  Anycast addresses are formally
defined in the IPv6 address architecture [RFC 2373], and are also being
used or proposed in a number of IPv4 contexts.

There are a large number of open issues regarding anycast addresses,
listed below.  The purpose of this BOF is to discuss these issues,
identify any additional issues, and determine what has to be done
to resolve them (e.g. find volunteers to write one or more drafts,
perhaps propose establishment of an IETF working group).  The
known issues requiring resolution are:

	- more thorough definition of anycast semantics (what does
	  "nearest" really mean?  what happens if more than one
	  nearest member?  is delivery to at-most-one member,
	  at-least-one member, or something else?), including
	  defining special cases of anycast addresses (e.g.,
	  "cluster addresses")

	- pros and cons of having anycast addresses be syntactically
	  distinguished from unicast addresses, and of having "well-
	  known" anycast addresses?

	- effects on routing (how are they routed?  how can/should
	  they aggregate?  locally-scoped vs. global anycast addresses?
	  limits on usage due to routing scaling limits?)

	- transport protocol issues, e.g., supporting TCP connections
	  to anycast addresses

	- allowing hosts to be members of anycast sets -- requires
	  a host-to-router protocol like IGMP, but strongly

	- usage guidelines, e.g., anycast vs. multicast for resource
	  discovery?  local use vs. global use?

Attendees should have read the following documents in advance of the BOF:

	- RFC 1546, Host Anycasting Service

	- RFC 2373, IP Version 6 Addressing Architecture (section 2.6)

	- RFC 2526, Reserved IPv6 Subnet Anycast Addresses

If you would like to present specific ideas/proposals to the BOF, or if
you know of other relevant documents that should be on the pre-reading
list, please send email to me Steve Deering <>.