Thursday, July 31, 2008

Proxy Server


A proxy server is a computer that offers network and internet access services to the client computers in a network. A proxy is a stand-in for you - someone who does something on your behalf. A proxy server is a kind of stand in for your computer. In an enterprise that uses the Internet, a proxy server is a server that acts as an intermediary between a workstation user and the Internet so that the enterprise can ensure security, administrative control, and caching service.
By using the proxy server you can hide, conceal and make your network id anonymous by hiding your IP address. A proxy server is associated with or part of a gateway server that separates the enterprise network from the outside network and a firewall server that protects the enterprise network from outside intrusion. In short, a Proxy Server can be described as 'A server that sits between a client application, such as a Web browser, and a real server.' To get the anonymous status on the network or Internet, strong intermediate methods are employed like cryptography etc.

How does Proxy Server works?

A proxy server receives a request for an Internet service (such as a Web page request) from a user. If it passes filtering requirements, the proxy server, assuming it is also a cache server , looks in its local cache of previously downloaded Web pages. If it finds the page, it returns it to the user without needing to forward the request to the Internet. If the page is not in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to request the page from the server out on the Internet. When the page is returned, the proxy server relates it to the original request and forwards it on to the user. A good example, and the one you probably see the most, is a web proxy. When configured to use a proxy, your web browser contacts the proxy server for each web access instead of going directly to the target server on the internet. The proxy server then turns around and makes the "real" request of the web server. The proxy server gets the response, and then passes it back to you.
There is a large number of the software available that allows you to hide your IP address with the help of the proxy servers. The well known software for this purpose is Hide IP, Stealth surf, Netconceal, Anonymous surfing, Proxify and Ghost surf. To the user, the proxy server is invisible; all Internet requests and returned responses appear to be directly with the addressed Internet server. (The proxy is not quite invisible; its IP address has to be specified as a configuration option to the browser or other protocol program.)

Types of Proxy Servers

Many different types of Proxy Servers are available. Some common types are-
  1. FTP
  2. HTTP
  3. Gopher
  4. IRC
  5. MSN
  6. AIM
  7. ICQ
  8. VOIP
  9. SSL
Depending on the purpose you can get Proxy Servers to route any of these common protocols, and many more. So out of the common types of Proxy Servers, you end up with the following:

FTP Proxy Server:
Relays and caches FTP Traffic.

HTTP Proxy Server:
A one way request to retrieve Web Pages.

Socks Proxy Server:
A newer protocol to allow relaying of far more different types of data, whether TCP or UDP.

NAT Proxy Server:
This one works a little different, it allows the redirection of all packets without a Program having to support a Proxy Server.

SSL Proxy Server:
An extension was created to the HTTP Proxy Server which allows relaying of TCP data similar to a Socks Proxy Server. This one done mainly to allow encryption of Web Page requests.

Furthermore, a Proxy Server can be split into another two Categories:

An Anonymous Proxy Server blocks the remote Computer from knowing the identity of the Computer using the Proxy Server to make requests.

A Transparent Proxy Server tells the remote Computer the IP Address of your Computer. This provides no privacy.

Anonymous Proxy Servers can further be broken down into two more categories, Elite and Disguised. An Elite Proxy Server is not identifiable to the remote computer as a Proxy in any way. A Disguised Proxy Server gives the remote computer enough information to let it know that it is a Proxy, however it still does not give away the IP of the Computer it is relaying information for.

Advantages of Proxy Server

Improve Performance
Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as America Online, MSN and Yahoo, for example, employ an array of proxy servers.

Security Schemes
Proxy servers can also implement security schemes. For example, an FTP proxy server could be set up to allow files to be sent from the Internet to a computer on the intranet,but to block files from being sent from the corporate network out to the Internet-or vice versa. In this way, intranet administrators can block anyone outside the corporation from downloading vital corporate data. Or they can stop intranet users from downloading files which may contain viruses.

A proxy can also do logging.

Filter Requests
Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

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