The document provides instructions for installing and configuring the Squid proxy server on CentOS/RHEL 5. It describes using yum to install Squid, configuring the squid.conf file to define ACLs for allowed internal networks, starting the Squid service, verifying port 3128 is open, and opening the port in iptables firewall.

1. Install Squid on CentOS / RHEL 5
Use yum command as follows:
# yum install squid
Output:
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Reading repository metadata in from local files
Parsing package install arguments
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Package squid.i386 7:2.6.STABLE6-4.el5 set to be updated
--> Running transaction check
Dependencies Resolved
=============================================================================
Package Arch Version Repository Size
=============================================================================
Installing:
squid i386 7:2.6.STABLE6-4.el5 updates 1.2 M
Transaction Summary
=============================================================================
Install 1 Package(s)
Update 0 Package(s)
Remove 0 Package(s)
Total download size: 1.2 M
Is this ok [y/N]: y
Downloading Packages:
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Installing: squid ######################### [1/1]
Installed: squid.i386 7:2.6.STABLE6-4.el5
Complete!
Squid Basic Configuration
Squid configuration file located at /etc/squid/squid.conf. Open file using a text editor:
# vi /etc/squid/squid.conf
At least you need to define ACL (access control list) to work with squid. The defaults port is TCP
3128. Following example ACL allowing access from your local networks 192.168.1.0/24 and
192.168.2.0/24. Make sure you adapt 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
Save and close the file. Start squid proxy server:

2. # chkconfig squid on
# /etc/init.d/squid start
Output:
init_cache_dir /var/spool/squid... Starting squid: . [ OK ]
Verify port 3128 is open:
# netstat -tulpn | grep 3128
Output:
tcp 0 0 0.0.0.0:3128 0.0.0.0:* LISTEN
20653/(squid)
Open TCP port 3128
Finally make sure iptables is allowing to access squid proxy server. Just open /etc/sysconfig/iptables
file:
# vi /etc/sysconfig/iptables
Append configuration:
-A RH-Firewall-1-INPUT -m state --state NEW,ESTABLISHED,RELATED -m
tcp -p tcp --dport 3128 -j ACCEPT
Restart iptables based firewall:
# /etc/init.d/iptables restart
Output:
Flushing firewall rules: [ OK ]
Setting chains to policy ACCEPT: filter [ OK ]
Unloading iptables modules: [ OK ]
Applying iptables firewall rules: [ OK ]
Loading additional iptables modules: ip_conntrack_netbios_n[ OK ]