SSH – Gateway Ports and Forward Reverse Tunnels
SSH can create forward and reverse tunnels to transmit port data through the encrypted connection. You can create forward tunnels that link the local port of the client machine to the remote port on the server. You can create reverse tunnels that link the remote ports of the server to the local ports on the client. Forward tunnels are created using the -L option. Reverse ports are configured using the -R option. The forward and reverse tunnels work fine when working locally on the client machine, but if you want other hosts, at the client location, to connect to the tunnels you need to enable the gateway ports feature of ssh.
Gateway ports does not work with forward and reverse tunnels on Ubuntu 8.04, the long term support branch. The openssh version included in the repositories does not allow reverse tunnels, and forward tunnels combined, with the -G (gatewayports) option enabled. Forward tunnels do work with the gateway ports feature. Theoretically the option does try and work, but when you operate ssh using -VV you will see that during the connection process the reverse tunnel fails to create.
I think this is an old bug that may have been addressed. I do see posts about successes, therefore I’m inclined to think that new versions of openssh have addressed the bug.
Instead of installing a newer version of ssh I just implemented an alternative for hosts at the client location. I wanted to use a single computer as a gateway to ports located on a remote server. It would have been nice to consolidate all communications to a single ssh connection.
I ended up using http://haanstra.eu/putty/. Each workstation, at the client location, will establish a direct ssh connection bypassing the gateway ports feature. There will be many ssh connections, but this is all behind the scenes stuff that the employees will never see, and it will provided the needed functionality.