Let's assume that Destination's IP is 192.168.20.55 (Linux box that you want to access).

You want to access from Linux client with IP 138.47.99.99.

Destination (192.168.20.55) <- |NAT| <- Source (138.47.99.99)

1. SSH from the destination to the source (with public ip) using command below:

ssh -R 19999:localhost:22 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

* port 19999 can be any unused port.

2. Now you can SSH from source to destination through SSH tuneling:

ssh localhost -p 19999

3. 3rd party servers can also access 192.168.20.55 through Destination (138.47.99.99).

Destination (192.168.20.55) <- |NAT| <- Source (138.47.99.99) <- Bob's server

3.1 From Bob's server:

ssh This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

3.2 After the sucessful login to Source:

ssh localhost -p 19999

* the connection between destination and source must be alive at all time.

Tip: you may run a command (e.g. watch, top) on Destination to keep the connection active.