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To close the tunnel, abort or kill the according ssh process (ctrl-c, evtl. after fg to get it back to the foreground).
Additional Notes:
Forwards (-L resp. Forward) and reverse forwards (-R resp. RemoteForward) can only be applied to sockets, like ~/.gnupg/S.gpg-agent if the socket to listen on is not yet owned by some daemon.
Hopping can be done automatically using ProxyJump option.
Putty
Putty is the most common ssh client for Windows. Hints for setting up key-based ssh access with Putty can be found everywhere on the internet, we'll focus on tunneling here.
Just one hint anyway: With ssh keys, have pageant running. Simply double-klick the .ppk file or even put it in your autostart group.
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