RE: [squid-users] Does squid use UDP or TCP for it's DNS requests

# Yes, but how do you define a "larger DNS request" That is
# really just a
# zone transfer. A DNS request is a request for a single resolution. A
# request for a block of IP's or names or anything else is a
# full or partial
# zone transfer.

Normally, ordinary queries use UDP, and zone transfers use TCP.

However, DNS limits UDP queries and responses to about 500 bytes. If a
response would be larger than that, the server sends back up to 500 bytes
and sets the "truncated" flag. The client is then supposed to perform the
same query again using TCP, which is almost unlimited in the size of
response it can send (the limit is typically only exceeded by web hosting
organizations that feel the need to create a PTR record for every A record,
and they have thousands of names pointing to the same address).

So best to open up UDP and TCP.

Peter

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Received on Wed Feb 05 2003 - 06:55:41 MST