Usage of TCP/53

Peter Dambier peter at
Thu Sep 28 18:52:05 UTC 2006

Ralf Durkee wrote:
> I have a question about usage of the TCP port 53 by DNS servers in
> general, and BIND in particular.  I've heard it stated that only zone
> transfers use the tcp port, but it was my understanding that it could
> also be used in other circumstances to handle larger
> requests/responses.  Are there other uses of TCP/53?  What would they be?
> Thanks,
> -- Ralf Durkee, CISSP, GSEC, GCIH, GSNA
> Principal Security Consultant

All queries can be either UDP or TCP. Sometimes servers, routers or
firewalls are broken and TCP is your only chance.

Address spoofing attacks dont work with TCP because they are building
a session. In the long run some people would like to get rid of UDP
and use TCP only, especially on open resolvers.

Kind regards
Peter and Karin

Peter and Karin Dambier
Cesidian Root - Radice Cesidiana
Graeffstrasse 14
D-64646 Heppenheim
+49(6252)671-788 (Telekom)
+49(6252)750-308 (VoIP:
mail: peter at
mail: peter at

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