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Re: DNS Anycast as traffic optimizer?

  • From: Steve Francis
  • Date: Wed Sep 01 19:27:50 2004

Bill Woodcock wrote:

     On Wed, 1 Sep 2004, Steve Francis wrote:
   >>> I'm sure there is research out there...
   >> Why?  :-)
   > Usual - if I build it myself, will it work well enough, or should I pony
   > up for a CDN?

Uh, what about that makes you sure that there's research out there?


Oops, sorry, misread the question. I should have said "I expect there is research..." I was answering why I wanted to know, not why I expect there is research...

   > I thought it was standard best practice for availability, like for root
   > name servers.  I thought it was not a good "closest server" selection
   > mechanism, as you'll be going to the closest server as determined by BGP
   > - which may have little relationship to the server with lowest RTT.

And the lowest RTT doesn't necessarily have much to do with what's
closest. If you want lowest RTT, that's what the DNS client already does
for you, so you don't need to do anything at all.


Excellent point, thanks.
So there is no need to anycast the DNS servers and rely on BGP topology for selection.
Instead use bind's behaviour so that each resolving nameserver will be querying the authoritative nameserver that responds the fastest.
If I have inconsistest replies from each authoratitive name server, where each replies with the virtual IP of a cluster colocated with it, I will have reasonably optimised client's nameserver to web farm RTT.
Whether that is good for the client, remains to be seen, but it seems to be all that (most) commercial CDNs do.

That just makes it too easy....

Am I missing something else, or is it really that simple to replicate a simple CDN?


-Bill