Trying to forward port 80 to a different ip address

[Scott Adamson]

My setup is as follows:   eth0 - address     203.89.239.135 broadcast  203.89.239.255 mask        255.255.255.0   eth1 - address    192.168.0.81 broadcast 192.168.0.255 mask        255.255.255.0     eth1 is connected via a crossover cable to 192.168.0.51, which is the web server. I'm trying to get iptables to forward www requests coming in to 203.89.239.135 to this second machine at 192.168.0.51. I have read the howto on linuxdoc, plus the one on the netfilter site, they say to add something like     EXTERNAL_INTERFACE="eth0" INTERNAL_INTERFACE="eth1" IPADDR="203.89.239.135" IPADDR_INT="192.168.0.81"     PORTFWIP="192.168.0.51"       $IPTABLES -A FORWARD -i $EXTERNAL_INTERFACE -o $INTERNAL_INTERFACE -p tcp --dport 80 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT       $IPTABLES -A PREROUTING -t nat -p tcp -d $IPADDR --dport 80 -j DNAT --to $PORTFWIP:80 The packets seem to get redirected, as they don't go to the server at 203.89.239.135, they go nowhere. Can someone assist with this, I have have found little information on the web except for 'just put in this PREROUTING line and it works great!' kind of useless information. What else  is required to get this to work ?