Proxy server
A proxy server is a server (a computer system or an application program) that acts as a mediator for requests from clients seeking resources from other servers. A client connects to the proxy server and requests some service, such as a file, connection, web page, or other resource, available from a different server.
The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. The proxy’s main purposes are keep machines behind it anonymous (mainly for security) and speed up access to a resource (it is commonly used to cache web pages from a web server).
Proxy server types
Caching proxy server
- A caching proxy server accelerates service requests by retrieving content saved from a previous request made by the same client or even other clients. Caching proxies keep local copies of frequently requested resources. These machines are built to deliver superb file system performance
Web proxy
- A proxy that focuses on WWW traffic is called a "web proxy". The most common use of a web proxy is to serve as a web cache. Most proxy programs provide a means to deny access to certain URLs in a blacklist, thus providing content filtering. This is usually used in a corporate environment, though with the increasing use of Linux in small businesses and homes.
Content-filtering web proxy
- A content-filtering web proxy server provides administrative control over the content that may be relayed through the proxy. It is commonly used in commercial and non-commercial organizations (especially schools) to ensure that Internet usage conforms to acceptable use policy.
Some common methods used for content filtering include: URL or DNS blacklists, MIME filtering, or content keyword filtering. Some products have been known to employ content analysis techniques to look for traits commonly used by certain types of content providers.
Hostile proxy
- Proxies can also be installed in order to eavesdrop upon the dataflow between client machines and the web. All accessed pages, as well as all forms submitted, can be captured and analyzed by the proxy operator. For this reason, passwords to online services (such as webmail and banking) should always be exchanged over a cryptographically secured connection, such as SSL.
Intercepting proxy server
- An intercepting proxy (transparent proxy) combines a proxy server with a gateway. Connections made by client browsers through the gateway are redirected through the proxy without client-side configuration (or often knowledge).
Intercepting proxies are commonly used in businesses to prevent avoidance of acceptable use policy, and to ease administrative burden, since no client browser configuration is required.
Proxy software
- The Apache HTTP Server can be configured to act as a proxy server.
- ISA server is described by Microsoft as an "integrated edge security gateway"; it includes caching web proxy, caching reverse proxy, Firewall, VPN, NAT, content filter, SSL encryption, and other components.
- Novell BorderManager web proxy server, reverse proxy, Firewall and VPN end point.
- PHProxy is one of the oldest and most customized proxy scripts in use on the Internet. Many of the newer proxy scripts were inspired by PHPProxy.
- SSH Secure Shell can be configured to proxify a connection, by setting up a SOCKS proxy on the client, and tunneling the traffic through the SSH connection.
- Sun Java System Web Proxy Server is a caching proxy server running on Solaris, Linux and Windows servers that supports http/https, NSAPI I/O filters, dynamic reconfiguration, SOCKSv5 and reverse proxy.
- Squid is a popular HTTP proxy server in the UNIX/Linux world.
- WinGate is a multi-protocol proxy server and NAT solution that can be used to redirect any kind of traffic on a Microsoft Windows host.
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