Linux Gateway/Firewall with NAT

[Russell Seymour]

Afternoon to everyone,   I am trying to work out how to use iptables to create a firewall/gateway on Red Hat Linux and I having problems trying to isolate how to do what I need to do (hope that makes sense).   I have a DSL router that goes into one interface on the Linux box (external), the other interface on this box is connected to the internal LAN.   I (think) have worked out how to use iptables to setup a simple NAT relationship from the IP address on the external card to the internal so that I can use the internet on the LAN.   However I have an SMTP server in the internal LAN and I have an mx record for it on the internet.  What I want to do is put another IP address on the external interface (virtual IP??) and have that NAT’ed through to the internal IP address for the mail server on ports 25, 110, 389, 3389. Also all traffic is allowed outbound, but only selected services are allowed inbound for the primary external IP address.   Here are the questions:   Is this a possible setup using Linux and iptables? If the answer to 1 is yes then can someone point me in the right direction in terms of what I need to do?   If anymore information is required then please let me know.  Any help is greatly appreciated.   Regards,   Russell Seymour Boots Support Team Melbourne Street Leeds, LS2 7PS   Tel - 0113 234 5100 (switchboard) Mob - 07800 022218