Port Forwarding on a single Interface machine

[sajalrastogi]

Hi Everyone,

I am trying to set up an environment where I want to forward any request coming in on my Linux Cent OS machine on port 8081 to a Windows XP machine port No 8081. Both the machines have got single Interface and are on the same LAN.

I tried using iptables and shorewall for achieving the same but somehow they didn't seem to work.

For iptables I used the following rules:
iptables -t nat -A PREROUTING -p tcp -d 192.168.152.xx --dport 8081 -j DNAT --to-destination 192.168.152.yy:8081

I am not sure why it is not working. Does it have to do anythg the single Ethernet card on the source machine(192.168.152.xx). Do I need to necessarily have two interfaces on the source to get this working.

Please guide me how can I achieve the same and the best possible way to debug if I am using the correct steps.

[Janos™]

You have to make sure your server allow the other server access the port 8081, so mostly you need to change your firewall. Have you enabled port forwarding in '/etc/sysctl.conf' ? Something like below you should try:

internet --> router --> centos ---> windows
IP --> router --> centos IP:1234 --> windows:3389

[sajalrastogi]

Hi Janos,

Thanks for your inputs.

I am sure that I have enabled the port forwarding in /etc/sysctrl.conf as well as allowed the required ports on the Cent OS machine using the IPtables. The ports on the windows machines are also accessible and have verified using by telnet on windows. But when I try using telnet on linux machine, on the using local host & fwd port, I have observed that it just get stuck on "trying to connect with 127.0.0.1" .


Is there any better way to try and debug the problem? Also, Is it possible or not to test the port forwarding using localhost or IP address from the same machine, or do I need to test it though the Internet or the Router?

Regards,
Sajal