Introduction to Proxy Servers in Computer Networking

Privacy and speed are among the benefits

PROXY server

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A proxy server acts as an intermediary between the two ends of a client/server network connection. Proxy servers interface with network applications, commonly with web browsers and servers. In corporate networks, proxy servers are installed on specially designated internal (intranet) devices. Some internet service providers (ISPs) employ proxy servers as part of their services. There's also a category of third-party hosted websites called web proxy servers that are available to internet users for web browsing sessions.

Proxy Servers, Firewalls, and Content Filtering

Proxy servers traditionally provide firewall and network data filtering support, network connection sharing, and data caching.

Proxy servers work at the application layer (layer 7) of the Open Systems Interconnection (OSI) model. Proxy servers differ from traditional network firewalls that work at lower OSI layers and support application-independent filtering. Proxy servers are also more difficult to install and maintain than firewalls because the administrator must configure proxy functionality for each application protocol (such as HTTP, SMTP, and SOCKS) individually. However, a properly configured proxy server improves network security and performance for the target protocols.

Network administrators often deploy both firewall and proxy server software to work in tandem, installing both firewall and proxy server software on network gateway servers.

Because proxy servers function at the OSI Application layer, the filtering capability of proxy servers is more sophisticated compared to ordinary routers. For example, proxy web servers check the URL of outgoing requests for web pages by inspecting HTTP messages. Network administrators can use this feature to bar access to illegal domains but allow access to other sites. Ordinary network firewalls, in contrast, cannot see the web domain names inside HTTP request messages. For incoming data traffic, ordinary routers can filter by port number or IP address, but proxy servers also filter based on application content inside the messages.

Connection Sharing With Proxy Servers

Years ago, third-party software products were used in home networks to share the internet connection of one computer with others. Now, home broadband routers provide internet connection sharing functions.

Not so with corporate networks, though. Corporate networks typically employ proxy servers to distribute internet connections across multiple routers and local intranet networks.

Proxy Servers and Caching

Web page caching by proxy servers improves a network's user experience in three ways:

  • Conserves bandwidth on the network, increasing its scalability.
  • Improves response time. With an HTTP proxy cache, for example, web pages load more quickly in the browser.
  • Increases content availability. Copies of web pages and other static content in the cache remain accessible even if the original source or an intermediate network link goes offline.

With the trend of websites to dynamic, database-driven content, the benefit of proxy caching has declined.

Web Proxy Servers

Many businesses deploy proxy servers that are physically connected to their internal networks. Most home networks don't use proxy servers because home broadband routers supply firewall and connection-sharing capabilities.

Web proxies, a separate class of proxy servers, allow users to take advantage of some proxy server benefits even when their local network doesn't support them. Internet users commonly seek out web proxy services as a means to increase privacy while online. These services offer other benefits, including caching. Some web proxy servers are free to use, while other charge service fees.