SSH Tunnel between to 2 computers using a gateway server

Question

I want to create an ssh tunnel between 2 computers. This is my current setup:

Fig. 1
---------     SSH     -----------     SSH    ---------
|   A   |  ---------> | Gateway | <--------- |   B   |
---------             -----------            ---------

Fig. 2
----------  :7575       Tunnel        :7575  ----------
| Server | <-------------------------------- | Client |
----------                                   ----------

A and B can SSH to the Gateway, but the Gateway cannot SSH to either A or B.

A runs on Linux and B runs on Windows and connects the gateway via PuTTY.

How can I create an tunnel (seen in Fig. 2) so that the client software on B can connect to the Server on A?

Answer 1

Like this:

• At B with putty: ssh to gateway. Right click window top, under connection ssh/tunnels add tunnel: localport 7575, destination 127.0.0.1:7575 - don't forget to click Apply before close.
• At S with OS ssh command: ssh -R7575:127.0.0.1:7575 gateway This reverse tunnel connects the end of the A-initiated tunnel to your port 7575 on B.