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Proxy Servers by Anthony Sequeira

Some clients are configured to forward their packets, which are seemingly destined for the Internet, to a proxy server. The proxy server receives the client's request, and on behalf of that client (that is, as that client's proxy), the proxy server sends the request out to the Internet. When a reply is received from the Internet, the proxy server forwards the response on to the client. Figure 9-19 illustrates the operation of a proxy server.

What possible benefit could come from such an arrangement? Security is one benefit. Specifically, because all requests going to the Internet are sourced from the proxy server, the IP addresses of network devices inside the trusted network are hidden from the Internet.

Yet another benefit could come in the form of bandwidth savings because many proxy servers perform content caching. For example, without a proxy server, if multiple clients all visited the same website, the same graphics from the home page of the website would be downloaded multiple times (one time for each client visiting the website). However, with a proxy server performing content caching, when the first client navigates to a website on the Internet, and the Internet-based web server returns its content, the proxy server not only forwards this content to the client requesting the web page but also stores a copy of the content on its hard drive. Then, when a subsequent client points its web browser to the same website, after the proxy server determines that the page has not changed, the proxy server can locally server up the content to the client, without having to once again consume Internet bandwidth to download all the graphics elements from the Internet-based website.

As a final example of a proxy server benefit, some proxy servers can perform content filtering to restrict clients from accessing certain URLs. For example, many companies use content filtering to prevent their employees from accessing popular social networking sites and promote productivity.

Note: A reverse proxy receives requests on behalf of a server and replies back to the clients on behalf of those servers. Reverse proxies can also be used with load-balancing and caching to better utilize a group of servers providing scalability and high availability.

About The Author

Anthony Sequeira, CCIE No. 15626, is a Cisco Certified Systems Instructor (CCSI) and author regarding all levels and tracks of Cisco Certification. Anthony formally began his career in the information technology industry in 1994 with IBM in Tampa, Florida. He quickly formed his own computer consultancy, Computer Solutions, and then discovered his true passion-teaching and writing about Microsoft and Cisco technologies. Anthony joined Mastering Computers in 1996 and lectured to massive audiences around the world about the latest in computer technologies. Mastering Computers became the revolutionary online training company, KnowledgeNet, and Anthony trained there for many years. Anthony is currently pursuing his second CCIE in the area of Security and is a full-time instructor for the next-generation of KnowledgeNet, StormWind.com. Anthony is also a VMware Certified Professional.

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