Question

I need to establish a Socket connection (TCP) between two hosts (say host1 and host2) in Java. But looks like I can’t do that because of a firewall. Though there’s a third host (say host3) which is accessible from both host1 and host2 and I think can be used as an intermediate for this connection.

So basically, I want to send a request from host1 (client) to host3, which redirects my request to host2 (server).

Could you please let me know how can this be achieved?

Thanks in advance!

Answer 1

You could establish a SSH tunnel with

ssh host3 -L4321:host2:6523

and then connect from host1 to host3 on port 4321. This effectively gets redirected to port 6523 on host2.

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A similiar option could be to have ssh provide a SOCKS server.

ssh host3 -D 6543

and then use curl instead of wget.

Then you can do

curl http://host2/foo/bar --socks4 localhost:6543

(untested, --socks4a and --socks5 could be an option as well…)

This ssh command creates a SOCKS server locally which tunnels the connection attempts to the ssh server, which in turn executes them.