tcp limitations

[Guy Pazi]

Hi, 
I am interested in blocking udp traffic, including dns udp queries and
replies, using a firewall. 
Our company is using an external dns name server placed on the public side
of the firewall. My question is, what bind versions allow tcp queries not
preceded by truncated udp queries (actually, not preceded by udp queries at
all). I've experienced some problems with that but couldn't really put my
finger on the whens and whats. I understood from my ISP's tech-support that
concurrent tcp queries are limited, but I couldn't get a figure from them.
Can a name server operate in a certain capacity over tcp?
Thanks Guy 



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