[dns-operations] Quick anycast primer

[Florian Weimer]

* Patrick W. Gilmore:

> 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?

Hard to tell because typical BGP decision processes prefer EBGP paths
over IBGP paths, before the BGP ID is considered.  I guess the
rationale for this behavior is that it's easier for the upstream AS to
decide on the best routing path.  After all, it's closer to the
destination and it might have better topology information (which is
certainly true for disconnected anycast clouds).