Sunday, December 11, 2011

what is proxy ?

Definition: proxy: In communications, a proxy is something that acts as a server, but when given requests from clients, acts itself as a client to the real servers. Analogy: Consider talking to somebody who speaks a foreign language through a translator. You talk to the translator, who receives your statements, then regenerates something else completely to the other end. The translator serves as your proxy. Key point: The communication terminates at the proxy. In other words, the proxy doesn't forward data so much as it tears it completely apart. For example, an HTTP proxy doesn't forward every request sent through it. Instead, it first examines if it already has the requested web page in its cache. If so, then it returns that page without sending another request to the destination server. Because proxies completely terminate the communication channel, they are considered a more secure firewall technology than packet filters, because they dramatically increase the isolation between the networks. Key point: You will occasionally be scanned for proxies. ISPs scan their users for proxies. Hackers scan the Internet looking for proxies they can anonymize their connections with. Certain servers (like IRC servers) scan clients for proxies in order to prevent anonymous connections. Several websites maintain lists of such proxies.


Proxy servers have two main purposes:

  • 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.
  • 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.

  • How do I use a Proxy Server?

     

    Proxy Types

    You may see references to four different types of proxy servers:

    Transparent Proxy

    This type of proxy server identifies itself as a proxy server and also makes the original IP address available through the http headers. These are generally used for their ability to cache websites and do not effectively provide any anonymity to those who use them. However, the use of a transparent proxy will get you around simple IP bans. They are transparent in the terms that your IP address is exposed, not transparent in the terms that you do not know that you are using it (your system is not specifically configured to use it.)

    Anonymous Proxy

    This type of proxy server indentifies itself as a proxy server, but does not make the original IP address available. This type of proxy server is detectable, but provides reasonable anonymity for most users.

    Distorting Proxy

    This type of proxy server identifies itself as a proxy server, but make an incorrect original IP address available through the http headers.

    High Anonymity Proxy

    This type of proxy server does not identify itself as a proxy server and does not make available the original IP address.
    Please make sure to read about anonymous proxy risks before using a proxy server.
    If you need further assistance using proxy servers please post a question in the proxy server forum.

    Browser Settings

    The following are instructions to configure various browsers to use an http proxy server.

    Internet Explorer 6 Proxy Server Configuration Screen
    Internet Explorer 6
    FireFox Proxy Server Configuration Screen
    FireFox
    Netscape 8 Proxy Server Configuration Screen
    Netscape 8
    Opera Proxy Server Configuration Screen
    Opera

    Instructions for Internet Explorer 6.0

    1. On the Tools menu in Internet Explorer, click Internet Options, click the Connections tab, and then click LAN Settings.
    2. Under Proxy server, click to select the Use a proxy server for your LAN check box.
    3. In the Address box, type the IP address of the proxy server.
    4. In the Port box, type the port number that is used by the proxy server for client connections (by default, 8080).
    5. You can click to select the Bypass proxy server for local addresses check box if you do not want the proxy server computer to be used when you connect to a computer on the local network (this may speed up performance).
    6. Click OK to close the LAN Settings dialog box.
    7. Click OK again to close the Internet Options dialog box.

    Instructions for Internet Explorer 5

    1. Click Start, point to Settings, click Control Panel, and then double-click Internet.
    2. Click the Connections tab, click LAN Settings, and then click to select the Use Proxy Server check box.
    3. In the Address box, type the appropriate proxy server information, and use the following format: http://
    4. Click Advanced, and then type the appropriate proxy settings in the Servers area. Use the following syntax for the proxy settings: http://
      : where
      is the Web address of the proxy server, and is the port number that is assigned to the proxy server. For example, if the proxy server's address is "proxy.example.microsoft.com" and the port number is 80, the setting in the Proxy Server box should appear like this: http://proxy.example.microsoft.com:80 Important: If you use a backslash (\) instead of a slash (/) in the proxy server's address, the settings disappear from the Proxy Server box and Internet Explorer does not find the proxy server.

    Instructions for Firefox 3.0

    1. Select the Tools Menu
    2. Select Options
    3. Select the Advanced Icon
    4. Select the Network tab
    5. Under connection select Settings
    6. Under Settings you can chose "Auto-Detect Proxy setting for this network" or "Manual Proxy Configuration"
    7. If choosing "Manual Proxy Configuration" Enter the IP address for the HTTP proxy server
    8. Enter the port of the HTTP proxy server
    9. Click Okay

    Instructions for FireFox 2

    1. Select the Tools Menu
    2. Select Options
    3. Select Connection Settings
    4. Select Manual Proxy Configuration
    5. Check Use the same proxy for all protocols
    6. Enter the IP address for the HTTP proxy server
    7. Enter the port of the HTTP proxy server
    8. Click Okay

    Instructions for Netscape 8.1

    1. Select the Tools Menu
    2. Select Options
    3. Select General
    4. Select Connection Settings...
    5. Check Manual Proxy Configuration
    6. Enter the proxy server's IP address in the HTTP Proxy field and the proxy's port into the Port field.
    7. OK your way out

    Instructions for Netscape 7.1

    1. Select the Edit Menu
    2. Select Preferences
    3. Maximize Advanced
    4. Select Proxies
    5. Choose Manual proxy configuration
    6. Enter the proxy server's IP address in the HTTP Proxy field and the proxy's port into the corresponding Port field.
    7. OK your way out

    Opera 8.5

    1. Select the Tools Menu
    2. Select Preferences
    3. Select Advanced Tab
    4. Select Proxy Servers
    5. Check the box next to HTTP
    6. Enter the proxy server's IP address in the first box and the proxy's port in the box after "Port"
    7. OK your way out

    Safari 2.0.3

    1. Select Preferences
    2. Select Advanced
    3. Select Proxies: Change Settings
    4. Check the box next to Web Proxy (HTTP)
    5. Enter the proxy server's IP address in the first box and the proxy's port in the box after the ":"
    6. Select Apply Now
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