A proxy server is used by an organisation to save having to set up an Internet connection for each of its users. It has two main functions:

1. It checks that the user is allowed to use that connection to access the Internet.


2. When a user wants to connect to the Internet, it translates their network IP address into something more relevant to the Internet. There could be many users connected to the Internet via the proxy server at any time, though, so it also tracks each session, ensuring that all the data going through the connection is passed to the correct destinations. Note: Please see the FAQ item What is a domain? for an explanation of what an IP address is, and how it works.

You can also use a proxy server to set up filters and various other types of rules, for example to block users in organisations from seeing inappropriate sites, to keep advertisements under control, or even to translate webpages into other languages.

According to research carried out by SurfControl, in 2003 the most popular types of sites blocked by IT departments in the UK workplace were:

• Adult/sexually explicit sites;
• Free web-based e-mail sites;
• Shopping sites;
• Auction sites; and
• Food and drink sites

Some types of proxy server can also maintain a local cache of recently requested webpages and files to reduce the amount of bandwidth used by the organisation.

If you cannot see the same content on a given website as a friend of yours reports, it is possible that there is a problem with local caching on one of your proxy servers and you should contact your ISP for help if the problem persists.

Proxy servers can also cause problems for home users developing their own websites: sometimes you may update and upload a file to your website and yet the aspect you altered remains unchanged in the browser view for a while. I have particularly noticed this happening with style sheets, and the problem is caused by the content being cached by the ISP's proxy server.

Even so, you will most likely be thankful to have a proxy server in use under normal circumstances:

• As indicated before, it can drastically reduce the length of time it takes to access popular websites that have problems keeping up with demand. As other customers of your ISP access it regularly throughout the day, the local cache will contain a reasonably up-to-date copy of parts of the site they have viewed, so that you don't have to wait on the 'real' website to respond.


• It can also give you a degree of protection against other users of the Internet trying to access your system without authorisation. Please note that if you are a home user, you should not rely on your ISP's proxy server to protect you from viruses, etc. Please see the Privacysense website for more details.

It is also worth mentioning that there are 'anonymous' proxies that claim to allow you to access the Internet anonymously. Most users of anonymous proxies simply want to keep their identities private, rather than to make trouble, and if they choose a reliable proxy, they should be pleased with the results. There are, however, methods that can be used to trace an individual on the Internet regardless of how the connection is made, but these are normally used by the authorities only in extreme cases of abuse.