Imagine the situation where you have 2 hosts:
- server – with public IP accessible via Internet
- client – with access to Internet but behind firewall so it is not accessible via Internet
You want to access client via SSH over the Internet but you can not access it because it is behind firewall that does not allow connections to the host via public IP.
My idea was to use reverse SSH tunnel started on client side, so I will be able to access client via server IP.
On your client you need to start SSH connection with something like:
ssh -f -T -N -R SERVER_IP:SERVER_PORT_TO_ACCESS_CLIENT:localhost:CLIENT_PORT_TO_ACCESS user@SERVER_PUBLIC_IP -p SERVER_SSH_PORT
If this works, you could access your client directly from server by using 127.0.0.1 since the reverse tunnel will listen only on localhost.
tcp 0 0 127.0.0.1:9999 0.0.0.0:* LISTEN
So your server is listening on localhost instead on SERVER_IP you ran on the client.
Chech your SSHd server configuration for example in file /etc/ssh/sshd_config following option should be enabled:
If it is not present you need to add it to your sshd_config and restart sshd.
tcp 0 0 0.0.0.0:9999 0.0.0.0:* LISTEN
You will be able to access your client port from any IP on server via port 9999 in this example.