It depends on what kernel version you are using. With 2.4 you can choose between doing postrouting or the easier prerouting. The difference is if you do a postrouting, all clients within your internal network (LAN) can connect and download/upload between each other. Postrouting is not necessary if you are the only client which uses DC behind the router/firewall. The examples below use the following settings: External Ethernet card: eth1, external IP 213.112.8.55, firewall (router) IP: 192.168.0.1, client IP: 192.168.0.2, external and internal port: 555

Linux 2.4, postrouting example

iptables -t nat -A POSTROUTING -d 192.168.0.2 -s 192.168.0.0/24 -p tcp --dport 555 -j SNAT --to 192.168.10.1

iptables -t nat -A POSTROUTING -d 192.168.0.2 -s 192.168.0.0/24 -p udp --dport 555 -j SNAT --to 192.168.10.1

iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 555 -j DNAT --to 192.168.10.2:555

iptables -t nat -A PREROUTING -i eth1 -p udp --dport 555 -j DNAT --to 192.168.10.2:555

iptables -t nat -A PREROUTING -d 213.112.8.55 -p tcp --dport 555 -j DNAT --to 192.168.10.2:555

iptables -t nat -A PREROUTING -d 213.112.8.55 -p udp --dport 555 -j DNAT --to 192.168.10.2:555

Linux 2.4, prerouting example

iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 555 -j DNAT --to 192.168.0.2:555

iptables -t nat -A PREROUTING -i eth1 -p udp --dport 555 -j DNAT --to 192.168.0.2:555

Linux 2.2, example

ipmasqadm portfw -a -P tcp -L 213.112.8.55 555 -R 192.168.0.2 555

ipmasqadm portfw -a -P udp -L 213.112.8.55 555 -R 192.168.0.2 555

Submitted by tajisen

How to use Shorewall to configure your iptables

Here's what you have to add to rules (assuming loc is the zone where your computer is located, 192.168.0.7 is your computer's IP, 666 is the port you wish to use and 123.45.67.89 is your external IP):

#ACTION

SOURCE

DEST

PROTO

DEST PORT

SOURCE PORT(S)

ORIGINAL DEST

DNAT

net

loc:192.168.0.7

tcp

123.45.67.89

DNAT

net

loc:192.168.0.7

123.45.67.89

Submitted by Ender

feedback form

feedback form

Any feedback you provide (corrections, updates or suggestions) are sent to the owner of this FAQ
and anyone else involved in writing or editing this item.

by USR56K edited by JMGullett
last modified: 2007-01-29 16:02:51