9. Port Forwarding: SSH Gateway Servers

As a rule its best to open machines up to as few addresses as possible; if you want to access your machines remotely from essentially the whole planet you should use a gateway (so you can focus on keeping just one machine really secure).

The following briefly describes how you can use a machine known as Cosmos as a gateway. (The example given is for a Unix/Linux-style command-line SSH client --- something similar should be possible for a Windows client.)

• The simplest method is to simply SSH into Cosmos and SSH to your own machine from there, however it is not easy to arrange secure X-sessions this way.
  
  
• Better, on your home (or other machine outside of UMIST), to login to your machine within UMIST (e.g frodo.shire.umist.ac.uk) use something like

          homemachine> ssh -L 2222:frodo.shire.umist.ac.uk:22 \
                                 cosmos.umist.ac.uk -l <frodo_username>

  which will yield a login prompt on cosmos --- login in the usual way. (This enlists cosmos to do some forwarding for you.) Then with a second SSH client on your home machine (e.g., in a second xterm)

          homemachine> ssh <homemachine> -p 2222 -l <frodo_username>

  or probably better

          homemachine> ssh 127.0.0.1 -p 2222 -l <frodo_username>

  i.e. local port 2222 is connected to port 22 on frodo.shire via cosmos.