How to configure putty for 3 hop ssh tunnel connection?

Question

How do I configure Putty for a 3 hop SSH tunnel connection? I know how to configure Putty for a 2 hop SSH tunnel connection, but now I am looking for a way to configure it with 3 hops. Can someone explain to me the procedure on how we can achieve it?

For two hops, I am following the below method.

Windows 10 (Putty) --> Linux Machine1 (192.168.1.100) --> Linux Machine2 (192.168.1.150)

• In the session window given the destination address (192.168.1.150) and port 22.
• In the Proxy option, I have given the intermediate server IP (192.168.1.100) and port 22.
• Also for the telnet command, I have given the following.

plink -agent -l %user %proxyhost -nc %host:%port

The above setup works fine for 2 hops. But now my requirement is a 3 hop SSH tunnel. How do i modify the current one and add 1 more hop?

Solution

It's not clear if you are just wanting to connect to an additional machine on the same network as Linux Machines 1/2 or if you need to jump to another network beyond them (for example Machine 4 on 172.22.1.x).

If you're simply trying to get to another machine on the same 192.168.1.x network as Linux Machine 1/2, use an actual SSH Tunnel (found under Putty's Connection -> SSH -> Tunnels menu). You can set up multiple tunnels to as many machines as you need to.

If you are actually trying to get to a third network, you can open up another instance of Putty that connects via a tunnel defined on your original Putty instance.

• Define a tunnel in Putty that forwards a port on your local machine (2222 for example) to Port 22 on Linux Machine2
• Then open another Putty instance on your Windows Machine that uses the tunnel (i.e. connect to Localhost:2222) AND defines a new tunnel to forward an additional port (2223 for example) to Port 22 on Machine4 (your 3rd hop).
• Open one more instance of Putty and connect to Localhost:2223 to access Machine4

I've only ever done this with 2 hops so I don't know how it will perform. It's not an ideal solution, but it may work if this is your only option.

Edit: If you're not limited to Windows/Putty, this (Transparent Multi-hop SSH) may do what you want. If you are limited to Windows, Cygwin may have some more flexible SSH tools.

Comments

[karthick87]

Yes my requirement is to get to a third network. I will try out this solution.. But just thinking if this could be configured in single putty instance.. Than creating 2 different instances.

[karthick87]

Actually host b can be accessed only from host a and host c can only be accessed from hostb. So from my windows machine i need to pass 3 hops to reach the destination (hosta, hostb, hostc).

[thephez]

I can't think of a way to do this without multiple Putty instances. Basically, you're using Putty as a virtual router to connect networks that aren't physically connected.