The St Andrews web proxy cache
What is a proxy cache?
A Web proxy cache is a mechanism for speeding up accesses to frequently used pages on the web and for reducing web traffic. Web browsers contact their local proxy cache to request a Web page and the cache stores the retrieved page on its local disk. The next person to access the same page is served the local copy from the cache, at local network speeds. If the page requested isn't in our local caches then the request is forwarded to the server specified in the URL.
The second function of the proxy cache is the proxying function - in this case the proxy acts on behalf of your machine and requests the page, or ftp download, or CGI request, from the remote web server (or ftp server etc.) This is normally used where client machines do not have direct access to the Internet, possibly for security or policy reasons, but it also makes the job of caching possible.
Access to licensed library material
One common reason for using the University's Web cache whilst outside the University network is to enable you to access restricted web pages and licensed databases which are only accessible from within University's network.
- To do this you must set up a Virtual Private Network (VPN).
If you are having problems with gaining remote access to specific Library resources, then please confirm with the Library that you are using the most appropriate mechanism for accessing this material.
What happens to out-of-date pages?
The proxy cache checks the original page to see if it has changed since it was cached; if it has changed, the cache downloads the newer version. If it hasn't changed then the cached copy is served. The protocol exchange to get the page's details takes much less time than retrieving the page itself.
How do I configure my browser?
PCs in the computer classrooms are set up automatically to use the proxy cache. There are two methods of setting up your browser to use the proxy cache: automatically, using an Automatic Configuration Script, or manually by entering the settings yourself. Both methods are explained below. If you wish to set it up on your own computer then what to do depends on which internet browser you are using.
We advise you to use the Automatic Configuration Script. If you have a laptop which you use sometimes within the University network and sometimes outside (for example on broadband at home) the Automatic Configuration Script enables you to access the Internet without changing the settings on your computer.
Using the automatic configuration script
Microsoft Internet Explorer
Select Internet Options in the Tools menu. From there, select Connections and from that window, click on LAN Settings. Tick the box for Automatic Configuration Script and enter the URL, http://www.st-andrews.ac.uk/st-and.proxy. Click OK to accept the changes.
Mozilla Firefox
Select Preferences in the Firefox menu or Options in the Tools menu. You may need to click on the Advanced tab, then choose Network and then click on Settings... to show the Proxies field. Choose the Automatic proxy configuration URL option and enter http://www.st-andrews.ac.uk/st-and.proxy. Click OK to accept the changes.
Netscape Navigator
Select Preferences in the Edit menu. Click on Advanced to show the Proxies field. Choose the Automatic Proxy Configuration URL option and enter http://www.st-andrews.ac.uk/st-and.proxy. Click OK to accept the changes.
Setting up the proxy cache manually
Microsoft Internet Explorer
Select Internet Options in the Tools menu. From there, select Connections and from that window, click on LAN Settings. Tick the check box for Proxy server and enter the Proxy DNS Hostname and Proxy Port number as shown below. Click Advanced... and tick the Use this proxy for all protocols check box. Click OK to accept the changes.
Mozilla Firefox
Select Preferences in the Firefox menu or Options in the Tools menu. You may need to click on the Advanced tab, then choose Network and then click on Settings... to show the Proxies field. Now select Manual proxy configuration; in the HTTP Proxy: and Port: boxes enter the Proxy DNS Hostname and Proxy Port number as shown below. Place a tick in the Use this proxy for all protocols check box then click OK to accept the changes.
Netscape Navigator
Select Preferences in the Edit menu. Click on Advanced to show the Proxies field. Choose the Manual Proxy Configuration option and enter the Proxy DNS Hostname and Proxy Port number as shown below. Click the Use these settings for SSL, FTP and Gopher button then click OK to accept the changes.
Proxy DNS Hostname: wwwcache.st-andrews.ac.uk
(both servers masquerade under this alias).
Proxy Port: 8080
How to turn off the proxy cache
If you have a portable computer which you usually use within the University network, you may need to re-configure it when you take it elsewhere.
Some technical details
There are in fact two servers providing the proxy/cache service. They work co-operatively. If you are using the automatic proxy script then it tries to share the load between the two servers. In order to spread the load equally between the two caches we use a technique called URL Hashing which calculates a value for each URL requested and then uses that value (mod 2) to select a cache. As well as load balancing this setup means that only one cache should store the pages from a site, removing any duplication between the caches. The software providing the service is SQUID.
