Squid is the most popular Linux system, a high-performance proxy service software, Web sites usually used as pre-caching service, the user can request instead of page data to the server and cached, Squid service program supports HTTP, FTP, SSL, etc. data cache multiple protocols, can control list (ACL) and access lists (ARL) to perform content filtering based on access and rights management capabilities, can also be based on a variety of conditions prohibit users from accessing inappropriate websites or threat resources.
When Squid caching proxy service program to provide services, with forward proxy mode and reverse proxy mode, forward proxy mode is divided into standard forward proxy mode, two kinds of transparent forward proxy mode.
Forward proxy mode, refer to allow users to access web pages and other resources by Squid service program, visit the Web site user behavior and to restrict the access control list (ACL) function. Use Squid service program to provide forward proxy service topology shown in Figure 16-1 
reverse proxy mode means that allows multiple hosts reverse caching node site data, thus speeding user access speed. The Squid reverse proxy service program provides services topology shown in Figure 16-2. 
When configured Yum repositories and good equipment to mount the mirror, you can install the Squid service program, service program Squid configuration file stored in the directory /etc/squid/squid.conf, Squid service package on the correct installation and after the start, the default would be able to provide users with a standard forward proxy mode service without the need to modify the configuration files individually or perform other operations. To use Squid service program provides a standard forward proxy mode service, you must fill out server in the browser's IP address and port number information. Squid service program uses the default port number for 3128,3401 and 4827.
Squid service program 3128,3401 and 4827 using the default port number, etc.
Transparent forward proxy mode configuration information without the user proxy server address and port number in the browser or other software, but by the DHCP server will assign network configuration information to the client host. Transparent forward proxy mode must advance the network configuration information and data forwarding configured, which forwards the completed SNAT technical data, allowing the data to the client host Squid proxy server, and then forwarded to the external network by the latter.
Reverse proxy mode Squid is an important service program, the principle is part of the original launch of the website source server to a user request to the server Squid cache node to handle.
Squid service program to configure a reverse proxy services, first find the IP address of a website source server, and then edit the master configuration file Squid service program, the port number 3128 to modify the site address and port number for the source server, this time being analytical service will be suspended (it can not be used in conjunction with a reverse proxy services). And write the desired website source reverse proxy server IP address information in the form of the following parameters, save and exit to restart the Squid service program. 
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