First of all we know about Proxy Server before knowing Transparent Proxy Server. Proxy servers are used to share an Internet connection with clients. A Proxy Server can be configured as the transparent Proxy Server. To share the Internet connection and Caching web server.

First of all to store web pages locally to improve performance. Proxy firewall to control access to the Internet. Squid Proxy is the most widely used open source proxy these software is used for Transparent Proxy Server.

Working Principle of Transparent Proxy Server


Squid Proxy Server quick key points

  • Packages – squid*.rpm
  • Port Numbers – 3128 (default)
  • Configuration File – /etc/squid/squid.conf
  • Service / Daemon – squid
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Squid Proxy Server Installation and Configuration

Firstly in Step-I (Install the Squid proxy packages) 

# yum install squid*

Secondly in Step-II (Edit the configuration file) 

# vi /etc/squid/squid.conf

First of all Modify the following parameters 

http_port 3128 transparent
visible_hostname linux?squid
cache_dir ufs /var/spool/squid 100 16 256
acl our_networks src 192.168.0.0/24
acl business_hours time S M T W H F A 09:00?17:30
acl test url_regex www.yahoo.com
http_access allow our_networks business_hours test

After that Step-III (Run the Natting script) 

# vim transparent_proxy.sh

Then Add The given line 

#!/bin/sh
SQUID_SERVER="192.168.0.12"
# Interface connected to Internet
INTERNET="eth0"
# Interface connected to LAN
LAN_IN="eth1"
# Squid port
SQUID_PORT="3128"
# DO NOT MODIFY BELOW
# Clean old firewall
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
# Load IPTABLES modules for NAT and IP conntrack support
modprobe ip_conntrack
modprobe ip_conntrack_ftp
# For win xp ftp client
#modprobe ip_nat_ftp
echo 1 > /proc/sys/net/ipv4/ip_forward
# Setting default filter policy
iptables -P INPUT DROP
iptables -P OUTPUT ACCEPT
# Unlimited access to loop back
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# Allow UDP, DNS and Passive FTP
iptables -A INPUT -i $INTERNET -m state --state ESTABLISHED,RELATED -j ACCEPT
# set this system as a router for Rest of LAN
iptables --table nat --append POSTROUTING --out-interface $INTERNET -j
MASQUERADE
iptables --append FORWARD --in-interface $LAN_IN -j ACCEPT
# unlimited access to LAN
iptables -A INPUT -i $LAN_IN -j ACCEPT
iptables -A OUTPUT -o $LAN_IN -j ACCEPT
# Load IPTA
# DNAT port 80 request comming from LAN systems to squid 3128 ($SQUID_PORT)
aka transparent proxy
iptables -t nat -A PREROUTING -i $LAN_IN -p tcp --dport 80 -j DNAT --to
$SQUID_SERVER:$SQUID_PORT
# if it is same system
iptables -t nat -A PREROUTING -i $INTERNET -p tcp --dport 80 -j REDIRECT --to-port
$SQUID_PORT
# DROP everything and Log it
iptables -A INPUT -j LOG
iptables -A INPUT -j DROP

After that Run the script 

# bash transparent_proxy.sh

Finally in Step-IV (Restart the squid service) 

# service squid restart

Linux Client Side Configuration

Firstly in Step-I (Refresh the network)

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# netconfig

Econdly in Step-II (Give Gateway ip as Proxy)

Finally in Step-III (Open browser and start browsing)

Congratulations now you have configured the Squid Proxy Server on CentOS and RHEL.