DNS problems to RoadRunner - tcp vs udp

Mike Lewinski mike at rockynet.com
Fri Jun 13 18:22:07 UTC 2008

Jon Kibler wrote:

> UDP is used for queries.
> TCP is used for zone transfers.
> If my server responded to TCP queries from anyone other than a secondary
> server, I would be VERY concerned.

That is a common, but incorrect, assumption.

DNS responses that are larger than the MTU of a single UDP packet are 
sent as TCP.

Back in the day (c. 1998) Microsoft had some arpa zones that they felt 
it necessary to create hundreds of PTRs per entry. Of course, they 
denied TCP to their nameservers. The end result is that our BIND8 server 
was crashing on the lookups (it was a crappy port to NT).

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