Iplementing a firewall after-the-fact

[Eric Wagar]

Is there a safe way to implement a firewall (ipchains/iptables) after
the fact?  After the fact being after I have already deployed the system
at a remote site?

I only have ports 21, 22, 25, 80, and 8080 needing to be public, with 53
needing to be open to the subnet.  Everything else needs to be turned
"off" or filtered.

thanks
eric
-- 
  Eric Wagar
  eric at deadhookers.org