North American Network Operators Group

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Re: How relable does the Internet need to be? (Was: Re: ConvergedNetwork Threat)

  • From: Alex Bligh
  • Date: Fri Feb 27 10:19:34 2004

--On 27 February 2004 14:52 +0000 Paul Jakma <[email protected]> wrote:

Because you always want to get to an E911 service in the same AS
You do or you dont? I dont see why anycast addresses need or need not
be restricted to same AS.
Anycast topology tends to follow AS topology, as people prefer their own
routes. So if there is anycast into (say) AS701 in DC (only),
and anycast into (say) AS2914 in every US city, then it would not be
unexpected for an AS701 customer in SF to reach the anycase node for in DC, as AS701 will in general prefer its own routes. If you
take a rural situation where you have your nearest (geographically) E911
service on some long link into Sprint, and the customer on some long link
into UUnet, it is most unlikely they will be close (network wise) Anycast
is arguable good for finding the best *connected* (i.e. closest using a
network metric) server, but is pretty hopeless for finding a closest (using
a geographic metric) server at anything much less than continental
resolution. Further, it is heuristic in nature. For (say) DNS, it doesn't
much matter if 1 in 50 queries go to a server far further away than they
need to. For E911, it does.