[dns-operations] opting in to stupid DNS tricks

Matthew Pounsett matt at conundrum.com
Wed Feb 23 14:14:39 UTC 2011

On 23-Feb-2011, at 08:06, Joe Abley wrote:

>> As an anycast DNS provider, my answer to this is: because BGP  
>> optimizes for the shortest AS path, not the shortest path, or the  
>> lowest RTT, or the most bandwidth, or the most capacity.  At  
>> $DAYJOB we give the same answer from everywhere, but we don't just  
>> rely on BGP to give great performance.  Anycast gives availability,  
>> and helps to sink regional DDoS.. it does not provide performance.
> I think this depends very much on what you're optimising for. For  
> any of the clouds that I have had a hand in deploying or running,  
> performance means availability, not RTT.
> If you expect your responses to be cached and answered from the  
> cache, then the incremental performance benefit in reducing the  
> initial cache miss by 100ms is close to zero; the performance  
> benefit in serving a (topological) region that otherwise can't get  
> an answer is enormous, however.

Exactly*.  CDNs are optimizing for more than just availability, and  
thus anycast is not the (only) answer for them.

* I actually define availability and performance as separate things,  
but it's clear we agree on the central point.

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