Ssh – Allow multiple remote connections to an ssh Dynamic forwarded port

port-forwardingsshssh-tunneling

Let us assume I have three machines

A – Server to which I am sshing to
B – Client from which I am sshing
C – Another Client in B's subnet

Now, I set up dynamic port forwarding for port 1235 by executing this in Client B 

ssh -D 1235 a@A

where a is the username at server A.

Now, I can connect to this port 1235 only from B as it is bound to localhost. If I modify the command as 

ssh -D C:1235 a@A

then only C can connect to the port 1235 of B and not B itself. There is a third option I could use, namely 

ssh -D 0.0.0.0:1235 a@A

whereby both B and C can connect to the port 1235 of B, but so can all the other machines in the same subnet as B and C. What I really want is a way to bind the dynamic port to allow only B and C to connect to it and not any other machine. How can I achieve this?

Best Answer

Use the -g option with SSH and then configure firewall rules to only allow C to connect to the port.

-g      Allows remote hosts to connect to local forwarded ports.

The command would then be:

ssh -g -D 1235 a@A
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