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University of Cambridge > Engineering Department > Help > Network Support > Offsite Access

Offsite access to internal web resources using web proxy forwarding

Important: This technique should only be used on a temporary basis where remote access to Engineering's internal web resources is a requirement. It should not be used for general offsite web browsing.

Setting up a Secure Shell connection

The following procedure requires a Secure Shell (SSH) client. There are a number of SSH clients available to choose from, a free Win32 Telnet/SSH client that has been used successfully by many within the Department is PuTTY which can be downloaded here.

When you install and run PuTTY you will be presented with a configuration screen. Most of the configuration options can be left at their default, the important settings for connecting to a machine at Engineering and creating a port forward entry suitable for web proxy purposes are given below.

For external access to Engineering's hosts it is necessary to enter the fully qualified domain name of the machine you wish to connect to, for example gate.eng.cam.ac.uk, and select SSH for the protocol:

The next step is to create a port forward tunnel entry so that once the SSH connection is established any traffic sent to the local network port 3128 is redirected to www-proxy.eng.cam.ac.uk:3128, the corresponding network port on Engineering's web proxy server:

Click Add to include the forwarding rule in your PuTTY session:

In order to make life easier in future it's worth saving your PuTTY session so that it can be reloaded at a later date:

Creating a desktop shortcut whose target points to the location of the PuTTY executable followed by the name of the session to launch provides a quick and easy means to connect, for example:

"C:\Program Files\PuTTY\putty.exe" -load gate.eng.cam.ac.uk

Note: The recommended Engineering infrastructure machine accessible from outside the University is:

gate.eng.cam.ac.uk

The first time you connect to a machine using SSH you will be presented with a warning:

This is normal and if you don't want to see the same warning each time you connect you should click Yes. Next you will be prompted to enter your Engineering Teaching System userid and password:

Once you have established the SSH connection you can minimise the PuTTY window.

Configuring web browser proxy settings

The next step is to configure your web browser to forward web traffic to port 3128 on your local machine so that it can be tunneled over your SSH session back to Engineering's web proxy server. The following example illustrates the necessary settings to change from within Internet Explorer, but the procedure is similar for other web browsers too. From Internet Explorer's Tools menu, select Internet Options..., followed by Connections and then finally LAN Settings... to bring up the web proxy settings:

Note: It is important that before you modify your existing proxy server settings you make a note of them so they may be re-entered after you have finished accessing Engineering's internal web resources via the PuTTY SSH connection.

Testing

After completing the above steps you should then be able to connect to internal web resources from your web browser and access information that is normally only accessible when connected to the departmental LAN. A simple test to verify this would be to try one of the following web pages:

Last updated: October 2006