ultradns reachability

Fri Jul 2 15:27:41 UTC 2004

In a message written on Fri, Jul 02, 2004 at 11:16:08AM -0400, Joe Abley wrote:
> In my opinion, the primary purpose of anycast distribution of 
> nameservers is reliability of the service as a whole, and not 
> performance. Being able to reach a server is much more important than 
> whether you can get a reply from a particular server in 10ms or 500ms.

Well, you're right, but there's a practical matter to scaling the
deployment.

If you have 50 anycast servers, each doing 1 unit of work, and you
list the anycast address 1 one non-anycasted address, there's a
real possibility that the vast majority of clients out there will
latch on to that one address, sending all 50 units of load towards
it.  So the question is not so much "is 500ms towards the server
bad", it's "can I build a single server (cluster) that will take
all the load worldwide when the client software does bad things."

Of course, everyone I've ever seen talk about this is either
referencing a lab test, or theory based on how the code works.  I've
seen very little real world measurements to show how this actually
plays in the wild.  If someone has anycast + unicast for a "busy"
zone and can provide real distribution of queries data (particularly
before and after an outage) that would be quite interesting.

-- 
       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
Read TMBG List - tmbg-list-request at tmbg.org, www.tmbg.org
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