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Proxy servers are as explained on this site, one of the most important components of a modern network infrastructure. No corporate network should allow ordinary desktop PCs or laptops to directly access the internet without some sort of protection. Proxy servers provide that protection to a certain extent as long as their use is enforced.
Most users, especially technically minded ones will often resent using proxies because they will be aware of the control that this entails. The simplest way is to ensure that configuration files are delivered automatically to the desktop by network servers. For example in a Windows environment this can be achieved using the active directory which can ensure desktops and users receive specific internet configuration files. For example, you can configure Internet Explorer using a specific configuration which is delivered to every desktop on login. In addition you can also use Active Directory to block access to install other browsers and configure them.
However although this allows you to control what browser and the internet route that each user will take – it doesn’t restrict what that user can do online. Another layer is required and most companies will employ some sort of content filtering in order to protect their environment. However as far as your proxy server is concerned content filtering will almost obviously have a major impact on performance.
One of the most common forms is that of URL filtering and this has one of the biggest performance impacts. This is largely due to the fact that this sort of filtering inevitably has many types of patterns to match against. Content filtering will severely impact the performance of a proxy server because of the sheer volume of data that is involved. Even running a nominal content filter against a UK VPN trial had a similar effect.
There are a variety of different types of filtering such as HTML tag filtering, virus screening or URL screening. It can be difficult though and the technology is developing all the time, for instance the ability to screen things like Java or ActiveX objects.
One of the biggest problems with content filtering and maintaining performance on the proxies is the fact that entire objects need to be processed. A proxy server will need to buffer the entire file, and therefore can only proceed with the transmission after the whole file has been checked. From the user perspective this can be frustrating as there will be long pauses and delays in their browsing especially on busy networks. Obviously this delay can be justified in the extent of screening for viruses, however this can be controversial for other screening issues.
Further Reference: Using a Paid VPN Service