What is a Proxy Server?
A proxy server is a computer server that provides computer network service to its clients for making indirect connections to other network services. A client connects to this proxy server and then requests a connection, files, documents, and resources available on other server. And proxy server provides the resources back to client either by connecting to specified server or by serving from its caches.
Web Proxy
A web proxy is proxy application that caches web page and files available on remote server, and allows local network clients to access the files more reliably or quickly.
Let us see how web proxy works. When a client sends a request for a Web resource (by entering a URL) and then the caching proxy will look for results in its local cache. If it found, it will return the file or document immediately. If not, it will fetch the file from the remote server and return the result to client, and save a copy in the cache. The cache, however, uses the expiry algorithms to remove the files or documents from the cache, according to their size, age, and access history.
Two common cache algorithms are Least Frequently Used (LFU) and Least Recently Used (LRU). LFU removes the least-frequently used documents, and LRU removes the least-recently used documents.
A web proxy can be used to filter which contents to be served. For example, censor-ware application attempts to block offensive Web contents. Some web proxies reformat content for a specific audience, for example, reformatting web page for cell phones or PDA. Web proxies can be used by network operators to intercept computer viruses or other malicious contents served by other remote Web pages.
Four Types of Proxy Servers
1) Transparent Proxy – This proxy acts as a proxy server and makes the original IP address available through the http headers. It is used for caching web site. It does not provide effective anonymity for users.
2) Anonymous Proxy – This proxy acts as a proxy server, but does not make the original IP address available. It is still detectable but provides a reasonable anonymity for most users.
3) Distorting Proxy – This proxy acts as a proxy server, but make an incorrect original IP address available through the http headers.
4) High Anonymity Proxy – This proxy does not identify itself as a proxy server and does not make the original IP address available.