How to setup ssh tunnelling in windows

Situation

You have a middle computer A, says OS is win7, the middle computer A connects to a inside computer B, which has access to inner network. And each time, you wan to access the inner network, you have to connect to the middle computer A first, and then connec to the inside computer B.
The problem is: Does it exists a way to direct connect to B from outside network. The answer is: Yes, it exists, and it’s ssh tunnelling.

How to do that?

1. First, setup port(22) forwarding in computer A(Win7). PortForwarding in Win7: E.g. We want to forward localhost(A):1234 to remote host(B) 192.168.1.5:22 netsh interface portproxy add v4tov4 listenport=1234 connectaddress=192.168.1.5 connectport=22

2. Enable firewall to accept data from port 1234 in computer A(win7) netsh firewall set portopening TCP 1234 ENABLE
3. That’s it. Now you access inside computer(B) from outside computer C, by run ssh <A-ip>:1234, is the ip of computer A.