linux - scp/sshfs on a remote 'not direct acessable' machine

Maybe the title must be changed but I have the following situation:

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  I can ssh to a host A

  
  


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  From A, I can ssh into a machine B, but this machine cannot be accessed from my computer. The name of the machine (as well as its ip) is local only.

  
  


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  How can I sshfs (and/or use scp) directly to machine B, without having to scp files from B->A and then from A->my machine. I'm really loosing productivity that way,

  
  

PS: I can't change configs in A nor B...

Answer

If you authenticate to B with credentials accessible on your computer (let’s call it W), for example a password/username tuple (rather than keys on A), you can build a SSH tunnel, for example:

W $ ssh -L 1234:B:22 A

and then

W $ ssh -p 1234 usernameB@127.0.0.1

or similarly with scp and sshfs. I. e. port 1234 on your local machine (usually 127.0.0.1 or ::1) is forwarded to B, port 22 from the perspective of A.