[squid-users] why is the UDP port for DNS queries kept "open"?

Hello!

I am using Squid 2.3stable4 (configures so that Squid does DNS lookups
itself), and I was wondering why the UDP port used by Squid for this purpose
is constantly kept "open" until Squid is shut down.
Wouldn't it be safer to use a separate UDP port for each new DNS query, which
is closed after the query has been answered or a timeout has occurred?
Personally, I don't like the idea of having a port accepting incomming data
all the time, which I cannot hide behind a firewall.
(Sorry if my terminology might be a bit incorrect, but I hope you still get
the idea...)

-- 
David Banz