Originally Posted by PresGas
iptables IS the firewall for Linux, or at least the front-end for netfilter of which is the firewall for Linux. Are you meaning an external firewall perhaps?
Yes, there is an external hardware firewall on my box or on the network held by the host, which presumably picks up the IP and associated rules. So, a http request would come in on port 80.
To forward it, do I need to open the external firewall as well as forward it in iptables?
The external firewall has no forwarding facility in this case so it has to be done through iptables.