What is an tunnel?
A tunnel is a way of forwarding many channels of information through a single channel.
One analogy is the Channel Tunnel. In Calais, cars, vans and lorries are all destined for the UK. They all drive on to the train, although they do not know what route the train takes. At the other end of the tunnel in Folkestone, they disembark and continue on their journey.
Applying it to network traffic, network data is collected at one point, transferred through the tunnel and then redistributed at another.
A useful application of tunnelling network traffic is to use protocols that are normally blocked by a firewall. Using SSH for this is a common method as many firewalls allow these connections that are both encrypted and authenticated.
The following instructions show how a tunnel can be set up using SSH to enable you to use RDP to connect to an Institute terminal server.
Open a terminal session on your computer. In the terminal session run the following on the command line:
ssh -L 3390:wts:3389
usernameis your Institute username. Enter your password when prompted and once you get a prompt just leave this terminal window open as it will ensure that the tunnel is running.
Installing Remote Desktop Connection Client
Download and install the client from http://www.maths.ox.ac.uk/help/faqs/login/tunnelling-rdp/mac/RDC103EN.hqx (More recent version can be downloaded from the Microsoft web site)
Starting the Remote Desktop Client
Start the Remote Desktop Client, In the window that appears, use "localhost:3390" as the computer you are connecting to.
Use the normal credentials that you normally use to log into Windows with. You may need to prefix the username with MATHS\, e.g. if your username is anybody, use MATHS\anybody.
If this worked OK, you should have a new window pop up that should be the the connection to the terminal server.