Clamd and Iptables

Running Clam on a separate machine to our Mail Transfer Agent we needed to configure iptables to allow access to clam from those machines. Clamd listens for connections on port 3310 by default but appears to hand off to other ‘passive’ ports for each stream to scan. So allowing access to port 3310 was not enough.
In the /etc/clamd.conf file I uncommented the following lines:

StreamMinPort 30000
StreamMaxPort 32000

To restrict the ports which clamd would use and restarted clam with

/etc/init.d/clamd restart

Checking netstat with:

netstat -lntap | grep clam

I could see that clam was indeed now using ports 30000-32000 rather than the default of 1024-2048
So adding the following line to /etc/sysconfig/iptables allowed the machines in my class B network to make use of the clam service:

-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 3310 –source -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 30000:32000 –source -j ACCEPT