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?

Are you using any standard protocol or your own custom protocol ? — Santosh, Dec 04 '11 at 08:15

score 4 · Accepted Answer · edited Dec 04 '11 at 15:27

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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.

edited Dec 04 '11 at 15:27

Udo Held

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answered Dec 04 '11 at 08:27

Tony Wang

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Wow! How did I forget this!! I have a question though! Can socat or netcat automatically reconnect if a connection is broken? – Muthu Dec 04 '11 at 08:42
I don't know if there is a built-in option to reconnect, but it can be client's job to reconnect if anything wrong – Tony Wang Dec 04 '11 at 08:53
This says "2011/12/04 15:52:25 socat[4328] E connect(3, AF=2 ipaddress:5000, 16): Address already in use". I tried the command with reuseaddr option also. – Muthu Dec 04 '11 at 10:28
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Just so that everybody is benefitted, the command I finally used "socat -d -d -d -d TCP4-LISTEN:9002,fork,reuseaddr TCP4:127.0.0.1:9000" which enables unlimited number of simultaneous connections. Thanks for the answer. – Muthu Dec 04 '11 at 12:44

score 2 · Answer 2 · answered Dec 04 '11 at 08:21

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

answered Dec 04 '11 at 08:21

Jomoos

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Will give this a try & confirm if this would suit. – Muthu Dec 04 '11 at 08:31

score 0 · Answer 3 · edited Apr 13 '17 at 12:13

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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.

edited Apr 13 '17 at 12:13

Community

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answered Dec 04 '11 at 08:33

sarnold

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Port Forwarding

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