ssh -R make target host accept connection on all interfaces

Question

I have a SOURCE host which is remote and behind NAT. I want to connect to SOURCE via ssh from a TARGET host which is in my home network. Thus I issue the following command on SOURCE:

ssh -R 2222:localhost:22 TARGET -N

Now from TARGET I can connect to SOURCE via ssh -p 2222 localhost. Fine

With TABLET in the same network of TARGET I would expect this to work:

ssh -p 2222 TARGET

Instead it looks like TARGET only accept connections on port 2222 from localhost. The following is on TARGET:

user@TARGET:~/$ netstat -l | grep 2222
tcp        0      0 localhost:2222          *:*                     LISTEN     
tcp6       0      0 localhost:2222          [::]:*                  LISTEN 

Is there a way to make the remote side of a ssh -R accept connections from all its interfaces?

Answer 1

By default, it will listen on localhost (loopback interface) only. You need to specify the bind_address as 0.0.0.0 in your command:

ssh -R 0.0.0.0:2222:localhost:22 TARGET -N

You need also to configure SSH daemon on target host to allow client to specify the bind_address. It is prohibited by default to listen to all interfaces. So, you will always find it listening on loopback even if you specifiy 0.0.0.0 as bind_address.

You need to have a line like the following in /etc/ssh/sshd_config to allow client to specify the bind address.

GatewayPorts clientspecified

When done, you can verify using netstat -lntp on target machine.