and that request is in turn relayed to the proxy server. The server will check to see if it has a cached version of this page and if not it will then go get it and relay it back to the workstation in question.
The nuts and bolts of it
If the above noted scenario still doesn’t make a whole lot of sense to you then think of it this way. Having such a proxy server will, for one, speed up the browsing experience for a corporate user. It is much faster to serve up a cached page then it is to retrieve it every time. When the proxy server or, in this case, the caching proxy receives a page request it will, as mentioned, check to see if it already has it. It will also see if the cached page has expired or not. Should the validity of the resource requested have expired then it will go and get a new copy of that resource. That alone makes it worth having a proxy server on a network. There are many other advantages to having one though. Those advantages very much impact the security posture of a corporate network as well, hence the prevalent usage of them. One of the most obvious advantages is being able to centralize all web page requests in one location. This will establish a chokepoint that can be exploited for security purposes.
The transparent proxy
Just as I mentioned above, having the ability to have all client requests go through a single computer gives one the ability to monitor client usage. By client I mean a corporate workstation. This centralization is done by configuring the client browser to use the transparent proxy server’s address. Though this definition of a transparent proxy is a popular one it is also incorrect. In reality a transparent proxy is a combination of proxy server and NAT technology. In essence client connections are NAT’d (network address translation) so that they can be routed to the transparent proxy. Having this type of setup is also a major pain, I am told, to implement and maintain.
The reverse proxy
What the devil is a reverse proxy you ask!? Good question indeed. Typically a reverse proxy is installed in close proximity to one, or several web servers. What in actuality happens is that the reverse proxy itself is the point of first contact for all traffic being directed at the web servers. Why go through the bother of this though? Well for several reasons actually. One of the primary ones is for security purposes as this reverse proxy is a first layer and acts as a buffer for the web servers themselves. Another reason is for SSL connections. Encryption is a computer intensive task and having it performed on the reverse proxy vice, the actual web server makes sense in terms of performance. Were the web servers themselves handling both the encryption part as well as the actual web server part then that machine would quickly become rather slow. For that reason the reverse proxy is equipped to handle the SSL connections and normally has some type of acceleration hardware installed on it for this very purpose.
Another key reason that the reverse proxy is employed is for load balancing. Think of a popular website that has a lot of visitors at any given time. It makes sense that there would be multiple web servers there to handle all incoming page requests. With a reverse proxy in front of these back end web servers no one box gets crushed but rather the load is balanced across all web servers. This certainly helps for overall performance. Another feature of the reverse proxy is the ability to cache certain content in an effort to further take a load off of the web servers. Lastly, the reverse proxy can also handle any compression duties that are required. All in all there is a tremendous amount of work being done by the reverse proxy.
Split proxies
Just when you think you’re done there is always something else! In this case that would be the split proxy. Well much as its name infers, the split proxy is simply a couple of proxies that are installed over a couple of computers. It’s that simple really. Although this type of proxy configuration is one that I have never come across, I have heard of them being used. One of its main selling points is the ability to compress data and that is a boon when slow networks are involved.
Wrap up
Over the course of this article we have seen the various types of proxies in use today in many corporate network environments. As we have seen many of them are used for specific reasons. There is not really one proxy type that can do it all, hence the variety of them. One of the greatest abilities of the proxy is to help enforce an acceptable usage policy on a corporate network. All too often we hear about someone who was fired for inappropriate use of company computer assets. What that neat use of the English language means is that someone was likely surfing for pornography from work and on company time no less in all likelihood. Even though someone doing this is acting foolishly and deserves to be terminated there are other reasons as well to control and monitor employee Internet usage. You can imagine for example how well it would go over for a high profile, publicly traded company to have an employee caught downloading kiddie porn. If that type of news hits the media all of sudden your company stock price could take a nose dive. Having a proxy in place within a corporate setting is really not only common sense, but also a necessity in reality. While most company employees are hard working and above board there will always be one or two who are not. Having the ability to catch and deal with them quickly is very much desired