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

["Patrick W. Gilmore" <patrick () ianai net>]

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