DNS Anycast as traffic optimizer?

Steve Francis sfrancis at fastclick.com
Wed Sep 1 21:40:52 UTC 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)




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