Linux Install & configure Squid in three easy steps

1. Squid configuration so that it will act as a transparent proxy

2. Iptables configuration
   

   • Configure system as router

   • Forward all http requests to 3128 (DNAT)

3. Run scripts and start squid service

First, Squid server installed (use up2date squid) and configured by adding following directives to file:
# vi /etc/squid/squid.conf

Modify or add following squid directives:


acl all src 10.1.51.66 10.1.51.89 10.1.51.95 10.1.51.225
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
acl to_localhost dst 127.0.0.0/8
acl SSL_ports port 443
acl Safe_ports port 80          # http
acl Safe_ports port 21          # ftp
acl Safe_ports port 443         # https
acl Safe_ports port 70          # gopher
acl Safe_ports port 210         # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280         # http-mgmt
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT
http_access allow manager localhost
http_access deny manager
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
http_access allow localhost
http_access allow all
icp_access allow all
http_port 3128
hierarchy_stoplist cgi-bin ?
access_log /var/log/squid/access.log squid
acl QUERY urlpath_regex cgi-bin \?
cache deny QUERY
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern .               0       20%     4320
acl apache rep_header Server ^Apache
broken_vary_encoding allow apache
coredump_dir /var/spool/squid

Where,

• acl all src 10.0.51.66  : Access control list, only allow LAN computers to use squid

• http_access allow localhost: Squid access to LAN and localhost ACL only

• http_access allow all: — same as above —

Here is the complete listing of squid.conf for your reference grep will remove all comments and sed will remove all empty lines:

# grep -v "^#" /etc/squid/squid.conf | sed -e '/^$/d'

Iptables configuration

Next, I had added following rules to forward all http requests (coming to port 80) to the Squid server port 3128 :
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 10.0.50.1:3128
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128