What Can a Proxy Server Do?
Proxy servers protect other computers from malicious attack, or overloading. They speed up access to information, or block access to it. They have many different functions all over the Internet, but one of their key characteristics is their correspondents do not know they exist. Proxy servers operate on behalf of other computers, breaking connections and diverting traffic from their intended destination.
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Basic Functions
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Network communications occur when a client contacts a server with a request and the server responds. The proxy server acts for either of these parties. When the proxy server acts on outbound traffic, protecting the client, it is a forward proxy server. When it intercepts traffic coming into a server, it is a reverse proxy server. In both cases, the client and the server are never in direct contact with each other. The client contacts the proxy, which then opens up a separate connection to the server. The server thinks the proxy is the client. In a reverse proxy scenario, the server is moved and a proxy is placed at its publicized address. The proxy receives all incoming connections and then refers to the server in order to fulfill those requests.
Forward Proxies
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Services of forward proxies fall into two categories: corporate and personal. A corporate proxy server enables a company to block access to certain sites from the computers within the private network. The proxy can also cache frequently requested data. A caching proxy notices when the same request is frequently repeated. It then stores the response so the next request for the same information can be fulfilled from its own memory, speeding up response times. The services proxies offer to private individuals are the ability to circumvent blocking proxies by masking the true destination of a request. Also, the forward proxy server is an "anonymizer," protecting the client's identity and enabling the user to circumvent regional restrictions on certain websites, such as TV station sites. In both categories, the response is checked and malicious software is filtered out; thus, the proxy acts as a firewall.
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Reverse Proxies
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All implementations of reverse proxies are corporate. The reverse proxy traps incoming requests. A number of different functions are available in this scenario. The reverse proxy server can also be a caching proxy, reducing load on a server and speeding up response times. Where demand for a service is greater than the capabilities of one server, the service provider installs a cluster of servers. Rather than requiring customers to try several different IP addresses, the proxy server stands as an access point to the cluster, presenting one unified IP address and distributing the work load among the many severs. The client never gains direct contact with the server, and the reverse proxy also offers firewall functions.
Demilitarized Zone
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A combination of forward and reverse proxy servers creates a demilitarized zone. A company wishes to protect the computers in its network and so installs firewalls and proxies to block incoming traffic. However, it may have a Web server to which it requires public access, and so these machines are placed outside the protected network. A reverse proxy then guards the otherwise vulnerable server. This creates an outer ring of protection which is called a demilitarized zone (DMZ).
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References
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