Why can I not connect to a reverse SSH tunnel port remotely, even with GatewayPorts enabled?

Question

I require constant SSH access to a host in our department, whose IP address is dynamically allocated. I've set up a remote SSH tunnel from the target host to one of our hosts that does posess a static ip address:

ssh -f -N -g -R :22223:localhost:22 tunnelhost

When I point SSH at local port 22223 on the tunnel host, the tunnel works fine. My problem is that I cannot seem to get the tunnel bound to anything other than localhost, though - i.e. when I try to SSH remotely to tunnelhost:12323, there is no open port to receive it. I've also tried:

ssh -f -N -R :22223:localhost:22 tunnelhost -o GatewayPorts=yes

But still no luck. Netstat shows me:

[me@tunnel_host ~]$ netstat -an | grep 22223
tcp        0      0 127.0.0.1:22223         0.0.0.0:*               LISTEN
tcp6       0      0 ::1:22223               :::*                    LISTEN

Confirming that the tunnel is only bound to localhost. I've added a port exception on the tunnel host, with firewalld-cmd, and ensured no network hardware is interfering with the connection. Any ideas as to what it could be?

Cheers, James.

Answer 1

You need to enable GatewayPorts=yes in the config for SSHd (/etc/ssh/sshd_config), not the client in order to enable binding to interfaces other than loopback on remote ports.

-o GatewayPorts=yes

Only works for local ports when passed to the ssh command.