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

Fri Feb 27 15:15:10 UTC 2004

--On 27 February 2004 14:52 +0000 Paul Jakma <paul at clubi.ie> wrote:

>> Because you always want to get to an E911 service in the same AS
>> number...
>
> 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 205.1.2.3/32 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
205.1.2.3/32 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.

Alex