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11.6. Proxy HTTP/FTP

Un proxy HTTP/FTP funciona como intermediaro para conexiones HTTP y/o FTP. Su rol es doble:
Falcot Corp eligió a Squid como su servidor proxy.

11.6.1. Instalación

The squid[2] Debian package only contains the modular (caching) proxy. Turning it into a filtering server requires installing the additional squidguard package. In addition, squid-cgi provides a querying and administration interface for a Squid proxy.
Antes de instalarlo, debe asegurarse que el sistema pueda identificar su propio nombre completo: hostname f debe devolver el nombre completamente calificado (incluyendo el dominio). Si no lo hace, entonces debe editar el archivo /etc/hosts para que contenga el nombre completo del sistema (por ejemplo, arrakis.falcot.com). El nombre oficial del equipo debe ser validado con el administrador de la red para evitar posibles conflictos de nombre.

11.6.2. Configuración de un caché

Enabling the caching server feature is a simple matter of editing the /etc/squid/squid.conf configuration file and allowing machines from the local network to run queries through the proxy. The following example shows the modifications made by the Falcot Corp administrators:

Ejemplo 11.22. The /etc/squid/squid.conf file (excerpts)

# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
#
include /etc/squid/conf.d/*

# Example rule allowing access from your local networks.
# Adapt localnet in the ACL section to list your (internal) IP networks
# from where browsing should be allowed

acl our_networks src 192.168.1.0/24 192.168.2.0/24
http_access allow our_networks
http_access allow localhost
# And finally deny all other access to this proxy
http_access deny all

11.6.3. Configuración de un filtro

squid itself does not perform the filtering; this action is delegated to squidGuard. The former must then be configured to interact with the latter. This involves adding the following directive to the /etc/squid/squid.conf file:
url_rewrite_program /usr/bin/squidGuard -c /etc/squid/squidGuard.conf
The /usr/lib/cgi-bin/squidGuard.cgi CGI program also needs to be installed, using /usr/share/doc/squidguard/examples/squidGuard.cgi.gz as a starting point. Required modifications to this script are the $proxy and $proxymaster variables (the name of the proxy and the administrator's contact email, respectively). The $image and $redirect variables should point to existing images representing the rejection of a query.
The filter is enabled with the service squid reload command. However, since the squidguard package does no filtering by default, it is the administrator's task to define the policy. This can be done by creating the /etc/squid/squidGuard.conf file (using /etc/squidguard/squidGuard.conf.default as template if required).
Debe regenerar la base de datos de trabajo con update-squidguard luego de cada modificación al archivo de configuración de squidGuard (o uno de las listas de dominios o URLs que menciona). La sintaxis del archivo de configuración se encuentra documentada en el siguiente sitio web:


[2] The squid3 package, providing Squid until Debian Jessie, is now a transitional package and will automatically install squid.
[3] PICS has been superseded by the Protocol for Web Description Resources (POWDER system: https://www.w3.org/2009/08/pics_superseded.html.