[62440] in North American Network Operators' Group
Re: DNS anycast considered harmful (was: .ORG problems this evening)
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Thu Sep 18 10:34:36 2003
Date: Thu, 18 Sep 2003 16:22:15 +0200 (CEST)
From: Iljitsch van Beijnum <iljitsch@muada.com>
To: Leo Bicknell <bicknell@ufp.org>
Cc: <nanog@merit.edu>
In-Reply-To: <20030918140558.GB23973@ussenterprise.ufp.org>
Errors-To: owner-nanog-outgoing@merit.edu
On Thu, 18 Sep 2003, Leo Bicknell wrote:
> A truely robust anycast setup has two "addresses" (or networks, or
> whatever), but only one per site. From the momentary outage while
> BGP reconverges to the very real problem of the service being down
> and the route still being announced there are issues with all anycast
> addresses going to one site.
Yes, this is the fatal miscalculation in the ultradns setup.
However, the other aspect, hiding most servers and only showing two at
a time, isn't exactly the best idea ever either. First of all, it limits
the number of usable DNS servers available at any specific location
unnecessarily, and second, BGP metrics are a very poor substitute for
RTT measurements.
