In a message written on Thu, Sep 18, 2003 at 09:57:23AM -0400, Todd Vierling wrote:
The problem with UltraDNS, the point which many on this people are missing, is that at least some UltraDNS sites are advertising *all* anycast networks simultaneously (see traceroutes below). Yes, all == 2 at the moment, but this argument holds for any value of "all".
Having just looked at this for some work functions I must agree. 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. Number your sites from 1..N, have all odds announce one address, all evens the other. DNS servers will still use the closest (due to RTT checking), but will now also have a backup that does not go to the same site in steady state, but is still very close as well. I strongly suggest the UltraDNS people look at that configuration if they aren't doing it now. -- Leo Bicknell - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/ Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org