network problem

[Robin Becker]

After a recent change of ISP and hence our external IP address I find 
that our FreeBSD 6.1 apache http server appears to be invisible from 
outside our site. Port 80 requests just seem to hang whether done via a 
dns lookup or using the ip address. Checking the logs seems to indicate 
that no requests now arrive, but that we have seen some external 
requests since the ISP changed.

The https/sshd/mysql etc servers are still visible externally and the 
http server is visible on its local address and if you visit the 
external address from inside the network.

I suspect that either I've still got some misconfiguration on the 
server, gateway or or dns(although this seems less likely).

Alternatively the ISP might have some other block in place.

I've looked for the old IP address in /etc and found no usages the 
gateway appears to be correctly set up.

What tests can I do internally/externally to see what happens to my port 
80 packets?
-- 
Robin Becker