Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Get The TCP/IP Guide for your own computer.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)
                     9  TCP/IP Hypertext Transfer Protocol (HTTP)
                          9  HTTP Features, Capabilities and Issues

Previous Topic/Section
HTTP Caching Features and Issues
Previous Page
Pages in Current Topic/Section
1
23
Next Page
HTTP Security and Privacy
Next Topic/Section

HTTP Proxy Servers and Proxying
(Page 1 of 3)

In my overview of the HTTP operational model, I described how HTTP was designed to support not just communication between a client and server, but also the inclusion of intermediaries that may sit in the communication path between them. One of the most important types of intermediary is a device called a proxy server, or more simply, just a proxy.

A proxy is a “middleman” that acts as both a client and a server. It accepts requests from a client as if it were a server, then forwards them (possibly modifying them) to the real server, which sees the proxy as a client. The server responds back to the proxy, which forwards the reply back to the client. Proxies can be either transparent, meaning that they do not modify requests and responses, or non-transparent, if they do so in order to provide a particular service.

Note: The term “transparent proxy” can also be used to refer to a proxy that is interposed automatically between a client and server—such as an organization-wide firewall—as opposed to one that a user manually configures.


Benefits of Proxies

Since proxies have the ability to fully process all client requests and server responses, they can be extremely useful in a number of circumstances. They can be used to implement or enhance many important capabilities.

Security

Proxies can be set up to examine both outgoing requests and incoming responses, to address various security concerns. For example, filtering can be set up to prevent users from requesting “objectionable” content, or to screen out harmful replies such as files containing hidden viruses.

Caching

As I mentioned in the previous topic, it can be advantageous to set up a “shared cache” that is implemented on an intermediary, so resources requested by one client can be made available to another. This can be done within a proxy server.

Performance

In some circumstances, the existence of a proxy server can significantly improve performance, particularly by reducing latency. An excellent example of this is the proxy server that is used by my own satellite Internet connection.

Due to the distance from the earth to the satellite, it takes over 500 milliseconds for a round trip request/response cycle between my PC and an Internet server. If I load a Web page containing images, I would have to wait 500+ milliseconds to get the HTML page, at which point my browser would then have to generate new requests for each graphical element, meaning another 500+ millisecond delay for each.

Instead, my ISP has a proxy server to which I send my requests for Web pages. It looks through the HTML of these pages and automatically requests any elements such as graphics for me. It then sends them straight back to my machine, cutting the time required to display a full Web page drastically.

Key Concept: One of the most important types of intermediary devices in HTTP is a proxy server, which acts as a middleman between the client and server, handling both requests and responses. A proxy server may either transport messages unchanged or may modify them to implement certain features and capabilities. Proxies are often used to increase the security and/or performance of Web access.



Previous Topic/Section
HTTP Caching Features and Issues
Previous Page
Pages in Current Topic/Section
1
23
Next Page
HTTP Security and Privacy
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.