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Re: DNS Anycast as traffic optimizer?

  • From: Steve Francis
  • Date: Wed Sep 01 17:43:03 2004

Paul Vixie wrote:



not only is it bad dns, it's bad web service. the fact that a current
routing table gives a client's query to a particular anycasted DNS server
does not mean that the web services mirror co-located with that DNS server
is the one that would give you the best performance. for one thing, the
client's dns forwarding/caching resolver might have a different position in
the connectivity graph than the web client. for another thing, as-path
length doesn't tell you anything about current congestion or bandwidth --
BGP is not IGRP (and thank goodness!).


I'm aware that web clients are not colocated with the client's name server, and that BGP does not attempt to optimise performance.

However, I suspect that in most cases, the client is close enough to the name server, and the BGP best path is close enough to the best path if it were based on latency, that most clients would be happy with the result most of the time. I'm not aiming for 100%, just Good Enough.

I'd be interested in seeing any data refuting either of those points, but it looks like I may have to do it, see what I find, and go write my own research paper. :-)

(I have found data that client's name servers are incorrect indicators of RTT b/w 2 web locations and clients 21 % of the time, but not how incorrect...
http://www.ieee-infocom.org/2001/paper/806.pdf)