Java socket between 2 hosts on different subnets

Question

In Java, we can open a ServerSocket with new ServerSocket(port), and connect to it with new *Socket(server_adress",port)*;
But how to connect, if server is in a different network, while both networks are behind a NAT.

I know that there must be a solution. Skype and other applications already found it.

Any ideas ?

Regards, Andrew.

Are you actually having a problem if server and client are in different subnets or are you just assuming there's a problem? Show us some code you have tried and perhaps we can help you to resolve whatever problem you're having? — Don Roby
– Don Roby, Commented Jan 21, 2011 at 12:40
It doesn't matter wether the server and the client are on different subnets. What is the problem you are having? — adrianboimvaser
– adrianboimvaser, Commented Jan 21, 2011 at 12:40
this is less of a java question than a networking question really. you should give some more detail on the topology of your network (routers, NAT, IP addresses, ...) — sfussenegger
– sfussenegger, Commented Jan 21, 2011 at 12:42
There's 2 solutions, 1. Set up port forwarding in your router. 2. Do hole punching, like Skype does (expect to spend the better part of the year implementing this in a general fashion). — nos
– nos, Commented Jan 24, 2011 at 23:08

Richard · Accepted Answer · 2011-02-24 18:47:35Z

1

For a list of all the methods, some of which are used by Skype, see http://en.wikipedia.org/wiki/NAT_traversal

Once you've picked a method, use Google to search for a Java implementation of that method. (Or follow the links from that wiki page, e.g. http://jstun.javawi.de/ )

answered Feb 24, 2011 at 18:47

Richard

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