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Re: Return two locations or low TTL [was: DNS caches that support partitioning ?]
From: "Patrick W. Gilmore" <patrick () ianai net>
Date: Mon, 20 Aug 2012 06:56:53 -0400

On Aug 20, 2012, at 06:49 , "Dobbins, Roland" <rdobbins () arbor net> 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.

-- 
TTFN,
patrick



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