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

Thu Sep 18 14:22:11 UTC 2003

On Thu, 18 Sep 2003, Leo Bicknell wrote:

: 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.

Yup.  Of course, if what they really want is to bias it toward geographic
closeness, more than two would be needed.  One possible example:

tld0.ultradns.net -> advertised by everyone
tld1.ultradns.net -> advertised by odd servers
tld2.ultradns.net -> advertised by even servers

With the provision that tld0 shows up first in queries for the glue records
(for first-pick bias).

-- 
-- Todd Vierling <tv at duh.org> <tv at pobox.com>