From: Tripp Lilley <tlilley(_at_)perspex(_dot_)com>
Subject: Anycast and related frobs
Date: Mon, 26 Jun 2000 07:43:03 +0000 (/etc/localtime)
I throw myself upon the humble mercy of the gods that I might not make a
fool of myself (again) in front of the IETF. Nevertheless, here goes...
As I understand it, a goal of IPv6 Anycast is to provide implicit
connectivity to the "nearest" netwise instance of a given member of a
group of service providers. Now, granted, this is based on an "address",
not an address / port tuple, so it's more like a group of machines, than
service providers, right?
What work has been done to provide a "nearest service" type of implicit
addressing? From what I gather, SLP is for service *discovery*, but what
I'm really on about is not "what services are available", but "where can I
find *this* service, closest to me?"
At the 46th IETF in Washington there was a Anycast BOF, chaired by
Steve Deering. In there where a few presentations on diffrent aspects of
anycast. Then, when the question was raised to the floor on weither there
was a need to form a anycast group few hands where raised.
The conclusion was that the real need of Anycast was limited (i.e. DNS,
PIM RPs and possibly a few other services) and that no specific architecture
where needed. Whatever needed was allready there or few trimmings where
For instance was UUNETs usage of Anycast for PIM Rendez-vous Points presented.
They used a trick which seems to be accepted as the only thing really
required to acheive the anycast service. They uses an unicast IP address which
they set common for all the RPs that so require, then they insert this IP
address into the normal unicast routing and the routing will find the
"best" path. While it migth be a bit confusing that it is actually diffrent
physical positions this is really not diffrent than having a multihomed box
having access to widely separated network segments.
Mr. Ohta presented the usage of Anycast in DNS root server handling over
The GIA proposal was a proposal for a complete anycast architecture according
to the ideas as presented with IPv6.
Anyway, you check these presentations and the report from the meeting in case
you have not yeat done so.
So, there is even some form of Anycast support in IPv4.
I am sure that Mr. Deering, Mr. Alvestrand and Mr. Ohta can contribute further
on this issue if so required.