Visual guide to SSH tunnels https://robotmoon.com/ssh-tunnels/
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@angristan very nice aesthetics. One issue i see is with "ssh -L 192.168.0.1:5432:127.0.0.1:5432 ssh-server". The problem with that example is that the two port numbers are the same, so if someone must adapt that example to their own situation, they have to work out which position is for which port number.
@angristan But overall that guide really helps remedy a problem most guides have: it's hard to know what is "local" and what is "remote" (because every endpoint can be either depending on where you sit). But when your guide says "Note that 127.0.0.1 here is localhost from the viewpoint of ssh-server" it really helps clear that up.