The word proxy means "to act on behalf of another," and a proxy server acts on behalf of the client and the server. All requests from the clients to the Internet go to the proxy server first. The proxy evaluates them, and if allowed, re-establishes the requests on the outbound side to the Internet. Likewise, responses or initial requests coming from the Internet go to the proxy server to be evaluated. The proxy then talks to the client. Both client and server think they are communicating with one another, but, in fact, are dealing only with the proxy.
Address Translation and Caching
The proxy server is a dual-homed host with two network interfaces and two IP addresses. The IP address on the outbound side of the proxy is the one the Internet sees, and the address of the machine making the request is hidden to the outside world. Proxies are often used in conjunction with network address translation (NAT), which hides all the IP addresses of the client machines on the internal network. Proxy servers may also cache Web pages, so that the next request for that same page can be obtained much faster locally. See NAT and proxy cache.
Application Level and Circuit Level
Proxy servers are available for common Internet services; for example, an HTTP proxy is used for Web access; an FTP proxy is used for file transfers. Such proxies are called "application-level" proxies or "application-level gateways," because they are dedicated to a particular application and protocol and are aware of the content of the packets being sent. A generic proxy, called a "circuit-level" proxy, supports multiple applications. For example, SOCKS is a generic IP-based proxy server that supports TCP and UDP applications (see SOCKS).
Other Proxies
Without being called a proxy specifically, the Internet's e-mail system (SMTP) is an example of a proxy server because it stores and forwards messages. E-mail is not sent directly from client to client without going through the mail server. Likewise, the Internet's Usenet news system (NNTP) forwards messages to neighboring servers. See firewall.
A Proxy Server in a LAN
In this LAN server illustration, the proxy server sits between two routers in what is known as a \"demilitarized zone.\" See DMZ.
![]() | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Microsoft, Novell bolster Linux partnership
- Microsoft and Novell said Wednesday that the software giant will invest more into the companies' SUSE Linux partnership. As part of the agreement, Microsoft will buy an additional $100 million in SUSE Linux support certificates. The partnership all posts between Novell and Microsoft kicked off in November...
- Blog posts 2008-08-20
- HP delivers strong third quarter fueled by blades, international, notebooks
- HP on Tuesday reported fiscal third quarter earnings of $2 billion, or 80 cents a share, on revenue of $28 billion, up 10 percent from a year ago. Excluding items, HP reported earnings of 86 cents a share, 3 cents ahead of Wall Street estimates. Revenue also...
- Blog posts 2008-08-19
- Piecing together Microsoft's cloud-computing vision
- A new white paper, sponsored by Microsoft and written by the always entertaining consultant David Chappell, provides more clues about what the Softies are planning to unveil at this October's Professional Developers Conference. For anyone looking to understand how and where Red Dog, Zurich, BizTalk Services and SQL Server Data...
- Blog posts 2008-08-19
- News to know: IDF; Office 14; Google; Flash flaw; MobileMe; Zoho
- Here are today's notable headlines. You can get News To Know via email alert and RSS daily: Jason O'Grady: MobileMe subscribers get a 60 day extension Adrian Kingsley-Hughes: Is the "killer app" argument dead? More info on USB 3.0 emerges ...
- Blog posts 2008-08-19
- Microsoft unveils Application Server License Mobility change to ease some virtualization headaches
- Microsoft has quietly unveiled its much anticipated licensing change to ease virtualization: Application Server License Mobility. The licensing plan, quietly launched in a licensing brief on the company web site tonight, now allows customers to freely move VMs, virtual workloads -- and their respective licenses -- across multiple servers...
- Blog posts 2008-08-18
- My bad day with Windows Server 2003
- Today was not a good computer day. I had some good meetings (yes, actual good, productive meetings), finished a couple items on my to do list, and even got some of that good old Ikea furniture put together. The part of my job where I work with a...
- Blog posts 2008-08-18
- CISCO: Why the Olympics didn't melt NBC
- Yesterday I posted about how Limelight Networks was used as the primary caching content provider for NBCOlympics.com and lifted a huge burden off on the public Internet by leveraging relationships with last mile ISPs. It's an amazing story about how technology can be used to solve immense problems. ...
- Blog posts 2008-08-18
- DEFCON 16: List of tools and stuff released
- Guest editorial by Rob Fuller DEFCON, the 9000+ attendee hacker conference in Vegas has become a sort of hydra conference. It has become more like a global fair than what most people think of conferences; even the badge is highly...
- Blog posts 2008-08-18
- Delivering the Olympics: Akamai and Limelight respond
- Akamai disputes Limelight Networks' take on its infrastructure and my recent post, Limelight Networks: Why the Olympics didn't 'Melt' the Internet. Limelight, however, says its implementation facts are accurate and that it absolutely stands behind its words.Keep in mind that the two companies compete fiercely and have different takes on...
- Blog posts 2008-08-18
- From Metasploit to Microsoft: Skape goes to Redmond
- Metasploit developer Matt Miller, who for years frustrated Microsoft officials with the public release of Windows exploits, is heading to Redmond to join Microsoft's Security Science team. Miller, who uses the hacker moniker Skape,will work on improved ways to find security vulnerabilities and better software defenses through...
- Blog posts 2008-08-18
- Scratch that. Windows Server 2008 R2 still lives
- What do you do with a blog post that is so messed up that you can't even go in and edit it to fix it? That's my dilemma with my post from August 15 about Microsoft skipping over Windows Server 2008 R2 and proceeding direct to Windows 7 Server. by...
- Blog posts 2008-08-18
- IBM: The mainframe is back
- The company claims the mainframe is finding its way into emerging markets and holding strong globally, despite a shortage of related skills among IT workers The mainframe is finding its way into emerging markets and is still holding strong globally, according to an IBM executive. ...
- News items 2008-08-18
- Before Intel's big show, AMD launches an attack
- With Intel's annual conference set to start this week, AMD launched a pre-emptive strike in a press conference on Friday. AMD executives said the processor innovations you'll hear about next week are imitations of technology they introduced as much as five years ago, and Intel's Larrabee graphics...
- Blog posts 2008-08-18
- Maintain an automated networked database? GraphOn wants to sue you
- GraphOn is suing Google for patent infringement and the company appears to be doing a nice imitation of NTP, the company that made its name by suing Research in Motion. GraphOn is going for gold in the patent troll Olympics. In a statement Monday, GraphOn said it...
- Blog posts 2008-08-18
- Building the ecosystem: Citrix and Platform Computing
- David Roussain of Citrix and Peter Dyer of Platform Computing brought me up to speed on how the two companies are working together to provide a highly managable, agile computing environment based upon virtual machines supported by Citrix XenServer and Platform Computing's VM Orchestrator 4.0. ...
- Blog posts 2008-08-18
- News to know: Limelight's Olympics; Software prices; Wordcamp 2008; Windows 7 Server
- Here are today's notable headlines. You can get News To Know via email alert and RSS daily: Jason Perlow: Limelight Networks: Why the Olympics didn't 'Melt' the Internet Larry Dignan: Limelight by the numbers: Akamai's thorn? Podcast: CIO tells how he reduced impact...
- Blog posts 2008-08-18
- Radmin Deployment Package (zip)
- Radmin Deployment Package makes Radmin Server installation and setup very fast. Radmin Deployment Tool is designed to install, uninstall and upgrade Radmin Server remotely on any number of computers. The product includes Radmin MSI Configurator, which can create an MSI file with selectable Radmin Server settings. Radmin Activation Server enables...
- Software downloads 2008-08-18
- Limelight Networks: Why the Olympics didn't 'Melt' the Internet
- Limelight Networks: Why the Olympics didn't 'Melt' the InternetWe agree about content providers...But in my fantasy world you would not necessarily need a DVR you could pay extra for a download and you could get a stream anywhere with net access.It didn't melt but I think it got hot. ntntRE:...
- Discussion threads 2008-08-17
- BuddyPress, an open source competitor to FaceBook
- At Today's WordPress Camp in San Francisco - covered in detail by ZD's Andrew Mager here - Founder Matt Mullenweg discussed impressive growth for WordPress.com and WordPress.org. Page views grew from 1.5 billion to 6.5 billion/month with 120-160 million unique visitors, including a third from heavyweight media...
- Blog posts 2008-08-16
- Confirmed: Microsoft to proceed directly to Windows 7 Server
- Confirmed: Microsoft to proceed directly to Windows 7 ServerI wouldn't expect 7 Server in 2009The bottom line is MS has been very smart in releasing the client OS first and following later with the server release. Late 2009 for the client and sometime in 2010 for the server would...
- Discussion threads 2008-08-15
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
- Access the latest Intel and industry best practices
-
Designed specifically to address the concerns of senior IT managers at organizations with more than 100 employees, the Intel Premier IT Professional Program provides best practices via local and e-Seminars and a members-only Web site.
- View the Intel Premier IT Professional web-site tour >>
The Green Enterprise
-
- A look into the enterprise to explore eco-friendly practices and innovations. In this ZDNet video series learn about what's motivating green tech, and how green technologies are impacting IT. 0:42
-
Harnessing the power of waves
3:13
-
Planting solar gardens
5:06
-
Fill your car for $1.10 a gallon?
1:43
- All series videos »




