[SOLVED] SSH Forwarding, Double NAT, and LAN access

RickPoleshuck · 07-30-2022, 08:16 AM

I have 3 hosts in 2 LANs. Host A and B are in one LAN and host C is in another LAN. Host C has a persistent SSH tunnel to host A which allows me to connect from host A to host C. Can someone tell me how to make that tunnel available to host B?

From host A I can access

Code:

http://localhost:3456

which is tunneled to host C and that works perfectly. But I would also like to use

Code:

http://A:3456

from host B. Host B and host A are in the same LAN, no tunneling required.

This is how I create the SSH tunnel on host C

Code:

$ /usr/bin/autossh -o "ServerAliveInterval 10" -o "ServerAliveCountMax 3" -N -R 3456:localhost:3456 A.DOMAIN.NAME

I am guessing there is some configuration on host A's /etc/ssh/sshd_config that needs to be made.

I hope I have explained my problem clearly...

michaelk · 07-30-2022, 10:32 AM

The default setting in sshd_config is GatewayPorts no which will only bind remote ports to localhost. If set to yes it will bind to any port.

Code:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:3456          0.0.0.0:*               LISTEN

The output of the comand netstat -tunlp will show all zeros instead of 127.0.0.1. All zeros indicates the process is bound to all ports.

RickPoleshuck · 07-30-2022, 01:05 PM

Perfect!!!
Much thanks

Quote:

Originally Posted by michaelk

The default setting in sshd_config is GatewayPorts no which will only bind remote ports to localhost. If set to yes it will bind to any port.

Code:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:3456          0.0.0.0:*               LISTEN

The output of the comand netstat -tunlp will show all zeros instead of 127.0.0.1. All zeros indicates the process is bound to all ports.