[isp-bgp] BGP Anycast: one AS or several?

[Stephane Bortzmeyer <bortzmeyer@...>]

We are studying the BGP anycastisation of ".fr" name servers
(references: RFC 1546, http://www.ripe.net/ripe/docs/ripe-268.html,
http://www.nanog.org/mtg-0302/anycast.html and
http://www.isc.org/tn/isc-tn-2003-1.html).

I would like an advice on the current plan we have. Basically, we plan
to use only one AS for the anycast service and for the legacy unicast
service. Some people would prefer two separated AS, which is more
complicated, IMHO.

The plan:

Two prefixes, the legacy unicast prefix (which must continue to work,
because it is used by other TLD which may not want anycast), let's
call it UP/22, and the new anycast prefix, let's call it AP/24.

One AS, 2486.

One physical site, with a global anycast node and the legacy unicast
node. Its router announces UP/22 and AP/24 with the same AS as origin.

Several physical sites with only a local anycast node. Their routers
announce only AP/24 with the same AS, 2486.

The only problem I see is that "anycast only" sites will not accept
the announce for UP/22 (because their AS is in it) and so will not be
able to reach the legacy unicast prefix. Not a big problem, there is
no communication between nameserver sites, anyway and we can always
set up a static route.








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