http://easyfwgen.morizot.net/gen/Тука можеш да си генерираш правила за твойте нужди.
Ако не ти трябва цялото това нещо си копи само частта за пренасочването на порта.
Ето пример:
###############################################################################
#
# FORWARD Chain
#
# Deal with responses from the internet
iptables -A FORWARD -i eth1 -m state --state ESTABLISHED,RELATED \
-j ACCEPT
# Port Forwarding is enabled, so accept forwarded traffic
iptables -A FORWARD -p tcp -i eth1 --destination-port 80 \
--destination 192.168.1.1 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp -i eth1 --destination-port 80 \
-j DNAT --to-destination 192.168.1.1:80