Return two locations or low TTL [was: DNS caches that support partitioning ?]

Patrick W. Gilmore patrick at
Mon Aug 20 10:56:53 UTC 2012

On Aug 20, 2012, at 06:49 , "Dobbins, Roland" <rdobbins at> wrote:
> On Aug 20, 2012, at 5:24 PM, Patrick W. Gilmore wrote:
>> But I do not think returning multiple A records for multiple datacenters is as useful as lowering the TTL.
> Some folks do this via various GSLB mechanisms which selectively respond with different records based on the assumed relative topological distance between the  querying resolver and various server/service instantiations in different locations.

"Some folks" == "more than half of all traffic on broadband modems" these days.

However, I think you missed a post or two in this thread.

The original point was you need a low TTL to respond with a single A record or multiple A records which all point to the same datacenter in case that node / DC goes down.  Mark replied saying you can respond with multiple A records pointing at multiple DCs, thereby allowing a much longer TTL.

My question above is asking Mark how you guarantee the user/application selects the A record closest to them and only use the other A record when the closer one is unavailable.


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