On Tue, 19 Sep 2000, Ingram, Richard wrote:
> Port 53 UDP for queries and 53 TCP for zone transfers if required.
TCP is also used for returning the results if they don't fit inside a UDP
query (512 bytes if I remember correctly.) If the resolvers are used for
local resolution, or if hostnames or number of hosts for a query are too
large, TCP is necessary. I'm pretty sure TCP is also used if UDP doesn't
work (remember that Cisco routers under load will drop UDP before they'll
drop TCP.) I know at one point a query on at least one of AOL's resources
wouldn't fit in a UDP result (MX's for aol.com I think.)
Paul
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