As with many aspects of the behavior of the IPCop firewall, it is possible to alter the behavior of the firewalling rules in order to customize IPCop to meet a topology un-catered for by the default rules. Within the context of the firewall rules, IPCop has had a file since the 1.4-series release that allows users to specifically add their own firewall rules (
/etc/rc.d/rc.firewall.local). Since version 1.3, there have been iptables chains, CUSTOMINPUT, CUSTOMFORWARD, etc., allowing iptables rules to be added manually.
Specifically using iptables is out of our scope here, but we recommend that interested readers read:
The Linux iptables HOWTO at http://www.linuxguruz.com/iptables/howto/