[dns-operations] Quick anycast primer

Patrick W. Gilmore patrick at ianai.net
Fri Jul 14 17:39:13 UTC 2006

On Jul 14, 2006, at 12:19 PM, brett watson wrote:
> On Jul 14, 2006, at 1:24 AM, Jim Reid wrote:
>> And back again. This
>> was because the ISP I used in those days didn't peer with Nominum in
>> LINX. Their upstream provider did that at PAIX.
>> I suppose it all depends on what's meant by "topologically closest".
> indeed, that's a significant point about anycasting a service.  if
> the networks (ASNs) between the client and the resolver have poor
> peering, "topologically closest" may not mean what you had hoped it
> meant.

Actually, even if they do, it can still be ... interesting.

For instance, you are a very large provider who spans the globe.  You  
see several instances of an anycast NS called XYZ.ns.

You are personally sitting in Washington DC.  Your network peers with  
providers announcing XYZ.ns in DC, London, NYC, SJC, Tokyo, etc.  But  
it turns out the guy in Tokyo has the lowest IP address, and  
therefore won the tie-breaker since the AS_Path Length was the same  
to all the instances.

Guess where you are getting your queries answered?

BGP is the suckiest way to route packets.  Except, of course, for  
every other way to route packets.


P.S. I _LIKE_ Anycast.  But that doesn't mean there are no problems  
with it.

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