[155612] in North American Network Operators' Group
Re: Return two locations or low TTL [was: DNS caches that support
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Mon Aug 20 06:57:27 2012
From: "Patrick W. Gilmore" <patrick@ianai.net>
In-Reply-To: <0D76E838-979D-4902-8C68-35F8B20CDBE4@arbor.net>
Date: Mon, 20 Aug 2012 06:56:53 -0400
To: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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:
>=20
>> But I do not think returning multiple A records for multiple =
datacenters is as useful as lowering the TTL.
>=20
> 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" =3D=3D "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.
--=20
TTFN,
patrick
