zekkerj sempre prestativo, obrigado!
Se deixar a porta 53/tcp bloqueada, ao fazer o diagnostico de DNS através de alguns sites, como por exemplo no
http://dnscheck.iis.se, é identificado um erro como abaixo:
Name server ns1.mydomain.com (x.x.x.x) does not answer queries over TCP.
The name server failed to answer queries sent over TCP. This is probably due to the name server not correctly set up or due to misconfgured filtering in a firewall. It is a rather common misconception that DNS does not need TCP unless they provide zone transfers - perhaps the name server administrator is not aware that TCP usually is a requirement.