Port Forwarding

Question

I have a simple requirement of a software level port forwarding/tunnelling of socket based communication.

• I have a source server and port using Sockets. This is a java program which works both in windows and linux and this is irrelevant.
• I have devices which keep sending data to this port. There may be a bi-directional communication
• I want to redirect this data to another remote server and port. So for the clients they will not have to worry about change of ip address whenever I move my app server.

Are there any tools/deamon/service programs which I can use to configure and do this?

I tried SSH, but to my understanding this needs a SSH protocol enabled server. In my case this is not applicable. I also tried using JSch but this again is an implementation of SSH in java format.

Can someone throw some pointers? Is it possible to use iptables NAT in linux?

Answer 1

You can try netcat or socat (it's more powerful than netcat)

An example for socat to forward port 80 using tcp4:

socat tcp4-listen:80,fork tcp4:{another server}:{another port}

and refer to http://en.wikipedia.org/wiki/Netcat#Port_Forwarding_or_Port_Mapping for netcat

Both are not java-related.

Answer 2

There is a TCP/IP port forwarding utility named portforward available in code.google.com. It is entirely written in Java.

Answer 3

If you're running xinetd on your system already, it provides a simple port forwarding mechanism that might be useful if you're not running IPTables already.

If you are running IPTables, Server Fault has an excellent, short question with a very similar goal. Though I find it a bit terse more detailed documentation is available.