named listen on unrecognized udp port

[Simon Waters]

Markus Fischer wrote:
> 
> What is this port for? It changes when I restart bind.

BIND is both a server and a client in IP networking terms.

It listens on port 53 to answer questions, but asked questions
from an anonymous port to port 53 on other name servers. Many
operating systems allocate ports to the anonymous range from
1024 upwards, although Solaris now starts much higher.

The "query-source" option can be used to specify this port for
firewalling purposes. BIND can be made to ask questions from
port 53, this was the old BIND behaviour.