You want to make use of the ProxyCommand option of ssh. Here is an example that uses one machine to connect to another.

You can add the following to your ~/.ssh/config file.

Host viatunnel
  IdentityFile ~/.ssh/inside_server_rsa
  ProxyCommand ssh -i ~/.ssh/proxy_server_rsa [email protected] "nc inside.mynetwork 22"
  user myself

This will connect first to [email protected] and use that to make a connection to [email protected]

Now typing: ssh viatunnel will connect using this configuration.

The ProxyCommand line basically runs 'nc' on the first hop of your connection and establishes a tunnel to port 22 on the second server. Then the outside ssh uses that to connect.

See ProxyCommand here at the openssh manual

ssh proxy tunnel

ssh

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