# Simple port forwarding

I am in a bit of trouble as I am trying to setup a reverse proxy with and a second server. My idea was to get the firewall to forward https to the reverse proxy and port 29418 (gerrit ssh) to the second server. Now my cooperate IT guy says: CAN NOT! Either both ports go to server 1 or both ports go to server 2.

Ok, as a work around I tried to setup a port forwarding on the reverse proxy of port 29418 -> server2:29418

Details:

• Server1 IP: 10.0.0.132 and 192.168.10.2 on Ubuntu 12.04.2 LTS
• Server2 IP: 10.0.0.133 and 192.168.10.3 on Ubuntu 12.04.2 LTS

Now both https and port 29418 go from the firewall to 10.0.0.132, IT says that's the only way. :(

So please tell me how to forward from 10.0.0.132:29418 -> 192.168.10.3:29418 or 10.0.0.133:29418

When I am working on the 10.0.0.132 I can connect to both 10.0.0.133:29418 and 192.168.10.3:29418 so the ports are open.

-- Update --

My iptables -t nat -L looks like this:

root@dev:/root# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination
DNAT       tcp  --  anywhere             dev.example.com       tcp dpt:29418 to:10.0.0.133

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
root@dev:/root# cat /proc/sys/net/ipv4/ip_forward
1


In case someone else is looking for a way that actually works. Though @HorsePunchKid is right in his suggestion, I've found this walkthrough that fills in the missing steps:

http://www.debuntu.org/how-to-redirecting-network-traffic-to-a-new-ip-using-iptables/

In essence:

Enable IP Forwarding:

sysctl net.ipv4.ip_forward=1


iptables -t nat -A PREROUTING -p tcp -d 10.0.0.132 --dport 29418 -j DNAT --to-destination 10.0.0.133:29418


iptables -t nat -A POSTROUTING -j MASQUERADE


And that's it! It worked for me in any case :)

• This is the best answer I found on this subject. – Victor Piousbox Sep 19 '14 at 8:34
• Lost connection from my Docker container after using this solution. Had to delete the rule. Rule was working, but lost all other traffic. I don't recommend this. – Dyin Nov 19 '16 at 16:27
• iptables -t nat -A POSTROUTING -j MASQUERADE OH WOW... that's it, thank you! Spent hours searching web and figuring out. This is so simple and works. – shrimpwagon Apr 26 '18 at 14:22

If you have iptables installed on 10.0.0.132, I think this will be pretty straightforward:

iptables -t nat -A PREROUTING -j DNAT -d 10.0.0.132 -p tcp --dport 29418 --to 10.0.0.133


This says to send traffic coming in to 10.0.0.132 on port 29418 over to 10.0.0.133 instead, on the same port, prior to any other routing that 10.0.0.132 might try to do. If you run this command and have trouble with it, replace the -A flag with -D to remove it.

If you're looking to have this rule run automatically when 10.0.0.132 starts up, consider adding the above command as a "post-up" rule in /etc/network/interfaces.

• That's exactly what I did but it didn't work. I have uncommented the net.ipv4.ip_forward = 1 in /etc/sysctl.conf but I still get errors connecting to the 10.0.0.132:29418 – uncletall Jul 15 '13 at 2:39

If anyone searching for a temporary method, try the below solution.

    ssh -L 192.168.0.10:8080:10.0.0.10:80 root@10.0.0.10


The above command redirects all connections to the port 8080 on your base machine to 80 port of your virtual machine. You can test the working by accessing the web page http://192.168.0.10:8080, and it'll show you the web page on guest machine.

This applies to all ports :)

In the end I had to install pfSense as a router inside my ESXi server to route the traffic to the different VM's as I could not get it to work in Ubuntu.