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

["David Schwartz" <davids () webmaster com>]

> 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.

        Another issue is that packet loss has a huge affect on DNS resolve times.
For those of use who use high-performance recursive resolvers that track
packet loss and bias which name servers they use for each zone based on
that, we like to have as many geographically diverse DNS servers to pick
from as possible.

        DS