How does this part work: -R laptop-behind-nat:22:localhost:22 This should open port 22 on the ssh-j.com server and connect it back to the laptop-behind-nat:22

How does this part work: -R laptop-behind-nat:22:localhost:22 This should open port 22 on the ssh-j.com server and connect it back to the laptop-behind-nat:22 , but this is already open. So, you're doing some firewall trickery to redirect 127.0.0.1:22 to a different port based on the username? And sshd isn't listening on 127.0.0.1:22? If so, could a person also try: -R laptop-behind-nat:22:localhost:22222 -R laptop-behind-nat:22:localhost:22223 -R laptop-behind-nat:22:localhost:22224 And try to find other tunnels that are open? Or is this also handled somehow in the firewall? I always try to avoid using ports for tunnels if I can avoid it on multi-user systems for this reason. This means using Unix sockets as much as possible for the permissions/security aspects. However, that also means that whatever tool I'm using also has to support Unix sockets. And in your case it would mean letting random people create "file" sockets on a server, which isn't necessarily a good idea.