[101671] in North American Network Operators' Group
Re: Looking for geo-directional DNS service
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Tue Jan 15 12:59:59 2008
Cc: "Patrick W. Gilmore" <patrick@ianai.net>
From: "Patrick W. Gilmore" <patrick@ianai.net>
To: nanog@merit.edu
In-Reply-To: <Pine.SOC.4.61.0801150857210.13380@paixhost.pch.net>
Date: Tue, 15 Jan 2008 12:50:00 -0500
Errors-To: owner-nanog@merit.edu
On Jan 15, 2008, at 12:00 PM, Bill Woodcock wrote:
> On Tue, 15 Jan 2008, Hank Nussbacher wrote:
>> The Ultradns (now Neustar) Directional DNS service is based on
>> statically defined IP responses at each of their 14 sites so there
>> is no proximity checking done.
>
> Yes, and that's how anycast works: it directs traffic to the
> _topologically nearest_ server. So as long as there's a DNS server
> topologically near your data server, your users will get the
> topologically
> nearest of your servers. Which is why so many content folks _do_ roll
> their own: to ensure fate-sharing between the DNS traffic which
> effectively selects the data server, and the eventual data traffic.
>
> If you're doing things on the Internet, instead of the physical world,
> topological distance is presumably of much greater interest than
> whatever
> geographic proximity may coincidentally obtain.
Except Hank is asking for true topological distance (latency /
throughput / packetloss).
Anycast gives you BGP distance, not topological distance.
Say I'm in Ashburn and peer directly with someone in Korea where he
has a node (1 AS hop), but I get to his node in Ashburn through my
transit provider (2 AS hops), guess which node anycast will pick?
--
TTFN,
patrick
