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

Offsite access to Windows machines using Virtual Network Computing (VNC) forwarding

Installing and configuring VNC Server on the machine you wish to access remotely

To use VNC you will need to download and install appropriate software from here.

Note: The Free Edition should be sufficient for basic operation.

During installation only the VNC Server componenet is required, the VNC Viewer is optional. In order that the VNC server starts automatically with your PC select Register and configure VNC for Service-Mode and Start the VNC Server in Service-Mode:

As part of the installation you will be asked to configure the VNC server:

On the Authentication tab of the VNC Server Properties screen click Configure to set a password that will be used to connect to the VNC server remotely:

Click the Connections tab of the VNC Server Properties screen to check or set the Accept connections on port setting:

Unless you wish to connect to the server using a standard web browser with slightly limited functionality uncheck the Serve Java viewer via HTTP on port check box.

Important: To increase security on a machine with VNC access enabled it is recommended that the network port that VNC connections use is changed from the default of 5900. An attempt to compromise a Windows machine will often target the default VNC network port in order to try and gain login access, changing the default port helps prevent this type of attack.

The other tabs of the VNC Server Properties screen can usually be left at their default settings.

Once the VNC installation has completed successfully you should see a VNC icon in the system tray at the bottom right of the screen:

The VNC server installation is now complete.

Setting up a Secure Shell connection on the remote client

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 5900 is redirected to the corresponding network port on your departmental desktop machine, mypc.eng.cam.ac.uk:5900, where mypc is replaced by your Engineering hostname:

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.

Note: In order that the necessary network traffic can be forwarded over the SSH link to the remote computer PuTTY must be running with an appropriate port forward before trying to connect with the VNC Client.

Connecting with the VNC Viewer from the remote client

To use VNC you will need to download and install appropriate software from here.

Note: The Free Edition should be sufficient for basic operation.

During installation only the VNC Viewer component is required.

Once installation is complete, launch the VNC viewer from, eg. Start, Programs, RealVNC, VNC Viewer 4, Run VNC Viewer:

Insert localhost:5900 as the server and click OK to forward VNC traffic from your local machine over the SSH connection back to your Engineering desktop machine.

Note: The Options button allows you to refine some of the connection settings such as Colour & Encoding that can help improve performance when working over slow internet connections. Limiting the number of colours to Medium (256 colours) should be adequate for running simple desktop applications.

Last updated: January 2007