DNS anycast considered harmful (was: .ORG problems this evening)

Thu Sep 18 14:22:15 UTC 2003

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.