Forwarding ports with iptables not working?

Question

I have an ubuntu server (14.04.1) which is asking as a router for my network. It has an internet facing interface, eth0, and a second interface, eth1, for connecting to my 10.0.0.0 network.

I am attempting to forward TCP traffic directed to eth0 (for this example, lets say its IP is 118.94.79.113) to eth1 with an address of 10.0.0.1 for port 27016

I have attempted the following commands in sequence:

sudo echo "1" > /proc/sys/net/ipv4/ip_forward

sudo sysctl net.ipv4.ip_forward=1

sudo iptables -t nat -A PREROUTING -p tcp --dport 27016 -j DNAT --to-destination 10.0.0.104:27016

sudo iptables -t nat -A POSTROUTING -j MASQUERADE

but this doesnt seem to work at all, i cannot connect to 118.94.79.113:27016 to access the application running on 10.0.0.104:27016. Is it to do with it being across two interfaces or what?

Solution

Try adding -i eth0 to your PREROUTING entry and -o eth0 to your POSTROUTING entry and executing sudo iptables -A FORWARD -i eth1 -j ACCEPT

Comments

[James T]

just gave this a shot, postrouting cannot have an interface but other than that both other commands worked, still not able to access 10.0.0.104:27016 via 118.94.79.113:27016

[Ben]

My mistake. POSTROUTING should have been -o eth0

[James T]

Given that a shot, still no luck.. odd... EDIT: just noticed the protocol I'm trying to pass is UDP, DUH! ill edit the rules and come back with whether it worked or not.

[James T]

Yep that worked...