Squid cache

Squid is a popular free software (GNU General Public License ed) proxy server and web cache. It has a wide variety of uses, from speeding up a web server by caching repeated requests, to caching World Wide Web, Domain Name System and other computer network lookups for a group of people sharing network resources, to aiding security by filtering traffic. It is primarily designed to run on Unix-like systems.

Squid has been developed for many years and is considered very complete and robust. It supports many protocol, although it is primarily used for HTTP and File Transfer Protocol. Some support is available for Transport Layer Security, Secure Sockets Layer, and HTTPS [http://www.squid-cache.org/Doc/FAQ/FAQ-1.html#ss1.12].

=Web proxy=

Caching is a way to store requested Internet objects (e. g. data like web pages) available via the HTTP, FTP, and gopher protocol protocols on a system closer to the requesting site. Web browsers can then use the local Squid cache as a Proxy server HTTP server, reducing access time as well as bandwidth consumption. This is often useful for Internet service providers to increase speed to their customers, and local area networks that share an Internet connection. Because it is also a proxy (i.e. it behaves like a client on behalf of the real client), it provides some anonymous and security.

A client program (e.g. browser) either has to explicitly specify the proxy server it wants to use (typical for ISP customers), or it could be using a proxy without any extra configuration: transparent caching , in which case all outgoing HTTP requests are intercepted by Squid and all responses are cached. The latter is typically a corporate set-up (all clients are on the same LAN).

Squid has some features that can further help anonymous connections, such as disabling or changing specific header fields in a client (computing) s HTTP requests. See the documentation for header_access and header_replace for further details.

=Reverse proxy=

The above set-up—caching the contents of an unlimited number of webservers for a limited number of clients—is the classical one. Another set-up is [http://squid.visolve.com/squid/reverseproxy.htm reverse-proxy] or webserver acceleration (using httpd_accel_host). In this set-up, the cache serves an unlimited number of clients for a limited number of—or just one—web servers.

Suppose slow.example.com is a real web server, and www.example.com is a Squid cache server that accelerates it. The first time any page was requested from www.example.com , the cache server would get the actual page from slow.example.com , but for the next hour/day/year (matter of cache configuration) every next request would get this stored copy directly from the accelerator. The end result, without any action by the clients, is less traffic to the source server, meaning less CPU and memory usage, and less need for bandwidth.

It is possible for a single Squid server to serve both as a normal and a reverse proxy simultaneously.

=Compatibility=

Squid can run on the following operating systems: *Linux *FreeBSD *OpenBSD *NetBSD *BSDI *Mac OS X *OSF and Digital Unix *IRIX *SunOS/Solaris Operating Environment *NeXTStep *SCO Group Unix *AIX operating system *HP-UX

Recent versions of Squid will also compile and run on Windows NT with the Cygwin/GnuWin32 packages.

As of 2005, the current stable version is 2.5; there is also a 3.0 version in development.

=External links=

==Information==

*[http://www.squid-cache.org/ Squid Cache]- official project homepage *[http://www.benzedrine.cx/transquid.html Squid + PF]- Transparent proxying with Squid and PF. *[http://www.squid-cache.org/Scripts/ Logfile Analysis]- Squid-Cache list of logfile analyzers *[http://squid.visolve.com/squid/ ViSolve Squid Support]: manual, configuration tips, ...

==Add-ons==

*[http://www.squidguard.org Squidguard]- A flexible plugin for advanced filtering. *[http://dansguardian.org DansGuardian]- Smart filtering, can be used together with Squid. *[http://cord.de/tools/squid/calamaris/Welcome.html.en Calamaris]- Squid logfile report *[http://www.rraz.net/squeezer2/ Squeezer2]- Squid logfile report

==Check cache behaviour==

*[http://www.web-caching.com/cgi-web-caching/cacheability.py Web-caching.com]: check page cacheability *[http://analyze.forret.com Analyze.forret.com]: analyze HTTP headers and compare to Squid policy