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Install squid proxy on centos

Squid is a caching and forwarding web proxy. It has a wide variety of uses, from speeding up a web server by caching repeated requests; to caching web, DNS and other computer network lookups for a group of people sharing network resources; to aiding security by filtering traffic. Although primarily used for HTTP and FTP, Squid includes limited support for several other protocols including TLS, SSL, Internet Gopher and HTTPS.

Update yum repositories and packages by typing the below command
[root@hackthesec ~]# yum update
Step 1:- Install squid package and dependencies using the below command
[root@hackthesec ~]# yum install squid
By default squid configuration file "/etc/squid/squid.conf" will contains recommended minimum configuration  and squid caching feature will work without making any changes . Recommended minimum configuration will looks like the below
#
# Recommended minimum configuration:
#
acl manager proto cache_object
acl localhost src 127.0.0.1/32 ::1
acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1

# Example rule allowing access from your local networks.
# Adapt to list your (internal) IP networks from where browsing
# should be allowed
acl localnet src 10.0.0.0/8     # RFC1918 possible internal network
acl localnet src 172.16.0.0/12  # RFC1918 possible internal network
acl localnet src 192.168.0.0/16 # RFC1918 possible internal network
acl localnet src fc00::/7       # RFC 4193 local private network range
acl localnet src fe80::/10      # RFC 4291 link-local (directly plugged) machines

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

#
# Recommended minimum Access Permission configuration:
#
# Only allow cachemgr access from localhost
http_access allow manager localhost
http_access deny manager

# Deny requests to certain unsafe ports
http_access deny !Safe_ports

# Deny CONNECT to other than secure SSL ports
http_access deny CONNECT !SSL_ports

# We strongly recommend the following be uncommented to protect innocent
# web applications running on the proxy server who think the only
# one who can access services on "localhost" is a local user
#http_access deny to_localhost

#
# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
#
# 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
http_access allow localnet
http_access allow localhost

# And finally deny all other access to this proxy
http_access deny all

# Squid normally listens to port 3128
http_port 3128

# We recommend you to use at least the following line.
hierarchy_stoplist cgi-bin ?

# Uncomment and adjust the following to add a disk cache directory.
#cache_dir ufs /var/spool/squid 100 16 256

# Leave coredumps in the first cache dir
coredump_dir /var/spool/squid

# Add any of your own refresh_pattern entries above these.
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern -i (/cgi-bin/|?) 0     0%      0
refresh_pattern .               0       20%     4320
Step 2:- Now start squid service
[root@hackthesec ~]# service squid start
and type this below command to start squid service automatically while booting.
[root@hackthesec ~]# chkconfig --levels 235 squid on

Step 3:- Setup your web browser to access Internet through proxy server on port 3128

IE : Tools » Internet options »Connections » LAN settings » Choose "Use a proxy server for your LAN" » Type your Proxy server ip (192.168.1.11 ) and port no 3128

Firefox : Options / Preferences » Advanced » Network » Settings » Choose "Manual proxy configuration " » Type your Proxy server ip (192.168.1.11 ) and port no 3128

Step 4:- Browse some sites and check the access log file on proxy server
[root@hackthesec ~]# cat /var/log/squid/access.log
1343759484.645    265 192.168.1.15 TCP_MISS/304 477 GET http://platform.twitter.com/widgets.js - DIRECT/23.64.79.144 application/javascript
1343759484.681    309 192.168.1.15 TCP_MISS/304 839 GET http://apis.google.com/js/plusone.js - DIRECT/173.194.36.36 -
1343759485.005    178 192.168.1.15 TCP_MISS/200 495 GET http://www.google-analytics.com/__utm.gif? - DIRECT/74.125.236.142 image/gif
1343759502.763  20292 192.168.1.15 TCP_MISS/200 1898 CONNECT s-static.ak.facebook.com:443 - DIRECT/23.64.66.110 -
1343759502.765  20292 192.168.1.15 TCP_MISS/200 1898 CONNECT s-static.ak.facebook.com:443 - DIRECT/23.64.66.110 -
1343759723.040 240567 192.168.1.15 TCP_MISS/200 2904 CONNECT plusone.google.com:443 - DIRECT/173.194.36.41 -
1343759934.518    459 192.168.1.15 TCP_MISS/200 495 GET http://www.google-analytics.com/__utm.gif? - DIRECT/173.194.36.8 image/gif
1343759943.131   2186 192.168.1.15 TCP_MISS/200 8343 CONNECT www.facebook.com:443 - DIRECT/66.220.146.94 -
1343759943.266  10616 192.168.1.15 TCP_MISS/200 2790 CONNECT apis.google.com:443 - DIRECT/74.125.236.128 -
1343759943.267  10615 192.168.1.15 TCP_MISS/200 2228 CONNECT ssl.gstatic.com:443 - DIRECT/74.125.236.143 -
1343759950.875   2596 192.168.1.15 TCP_MISS/200 32219 CONNECT www.facebook.com:443 - DIRECT/66.220.146.94 -
1343759961.388  20443 192.168.1.15 TCP_MISS/200 1911 CONNECT s-static.ak.fbcdn.net:443 - DIRECT/23.64.77.177 -

Troubleshooting :
If you not able to browse using proxy settings , Disable the firewall ( iptables ) and selinux service on your squid proxy server .
Disable firewall ( Iptables ) :-
[root@hackthesec ~]# service iptables stop
[root@hackthesec ~]# chkconfig iptables off

Disable Selinux :- open the file /etc/selinux/config and find the line
SELINUX=enforcing
and replace with
SELINUX=disabled
now reboot the server and try step 4.

Configure squid proxy as web filter:
You can restrict user access to particular websites or keywords using access control lists (ACLs) .
Restricting Access to specific web sites :
For example , we can see how to block facebook.com and gmail.com .
Step 1:- create a file ( /etc/squid/blockedsites.squid ) and add the site names one per line.
[root@hackthesec ~]# cat /etc/squid/blockedsites.squid
#blocked sites
www.facebook.com
www.gmail.com
Step 2:- Open the /etc/squid/squid.conf and create a new acl " blocksites" and acl type "dstdomain" in the acl section like the below .
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT
# ACL blocksites 
acl blocksites dstdomain "/etc/squid/blockedsites.squid"
and add the following line "http_access deny blocksites" to http_section to deny the access to the acl "blocksites" .
# Recommended minimum Access Permission configuration:
#
# Only allow cachemgr access from localhost
http_access allow manager localhost
# Deny access to blocksites ACL
http_access deny blocksites
Step 3:- Now restart squid service
[root@hackthesec ~]# service squid restart
Step 4:- Try to access facebook.com in your browser . you could see the blocked page as below .

and check the log file you can see the facebook request is denied .
 [root@hackthesec ~]# tail -f /var/log/squid/access.log
.................................................................................
1343820985.542      1 192.168.1.15 TCP_DENIED/403 4255 GET http://www.facebook.com/ - NONE/- text/html
1343820986.998   1411 192.168.1.15 TCP_MISS/200 13152 GET http://www.squid-cache.org/Artwork/SN.png - DIRECT/198.186.193.234 image/png
1343820987.004      0 192.168.1.15 TCP_DENIED/403 4178 GET http://www.facebook.com/favicon.ico - NONE/- text/html

Restricting Access to specific keywords :
Step 1:- create a file ( /etc/squid/blockkeywords.squid ) and add the keywords one per line.
[root@hackthesec ~]# cat /etc/squid/blockkeywords.squid
#blocked keywords
sex
porn
xxx
Step 2:- Open the /etc/squid/squid.conf and create a new acl "blockkeywords" and acl type "url_regex" in the acl section
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT
# ACL blocksites 
acl blocksites dstdomain "/etc/squid/blockedsites.squid"
# ACL blockkeywords
acl blockkeywords url_regex -i "/etc/squid/blockkeywords.squid"
and add the following line "http_access deny blockkeywords" to http_section to deny the access to the acl "blockkeywords" .
# Recommended minimum Access Permission configuration:
#
# Only allow cachemgr access from localhost
http_access allow manager localhost
# Deny access to blocksites ACL
http_access deny blocksites
# Deny access to blockkeywords ACL
http_access deny blockkeywords

Restricting Access to specific Ipaddress :
Step 1:- create a file ( /etc/squid/blockip.squid ) and add the ip adresses one per line.
[root@hackthesec ~]# cat /etc/squid/blockip.squid
#blocked ips
192.168.1.20
192.168.1.21
Step 2:- Open the /etc/squid/squid.conf and create a new acl "blockip" and acl type "src" in the acl section
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT
# ACL blocksites 
acl blocksites dstdomain "/etc/squid/blockedsites.squid"
# ACL blockkeywords
acl blockkeywords url_regex -i "/etc/squid/blockkeywords.squid"
# ACL blockip
acl blockip src "/etc/squid/blockip.squid"
and add the following line "http_access deny blockip" to http_section to deny the access to the acl "blockip" .
# Recommended minimum Access Permission configuration:
#
# Only allow cachemgr access from localhost
http_access allow manager localhost
# Deny access to blockip ACL
http_access deny blockip
# Deny access to blocksites ACL
http_access deny blocksites
# Deny access to blockkeywords ACL
http_access deny blockkeywords

Allow Full access to specific Ipaddress :
You can allow specific ip address to gain full access without blocking sites and keywords . just create a file "/etc/squid/allowip.squid" and add the ip address one per line and create an acl "allowip"  and acl type "src" in the acl section
# ACL allowip
acl allowip src "/etc/squid/allowip.squid"
and add the "allowip" in the http_access as below
# Recommended minimum Access Permission configuration:
#
# Only allow cachemgr access from localhost
http_access allow manager localhost
# Deny access to blockip ACL
http_access deny blockip
# Deny access to blocksites ACL
http_access deny blocksites !allowip
# Deny access to blockkeywords ACL
http_access deny blockkeywords !allowip

Changing squid proxy port number:
You can change squid proxy port number , by default it uses 3128 port .
Just find the below line in "/etc/squid/squid.conf"
http_port 3128
and replace with
http_port 8000 # whatever port number you want

Restricting Download size :
You can restrict download file size  using reply_body_max_size .
Add the below line at the bottom of the http_access section
#Restrict download size
reply_body_max_size 10 MB all
or
#Restrict download size
reply_body_max_size 10 MB !allowip

Configuring Squid as Transparent Proxy :
You can configure squid as transparent proxy .
Step 1:- just find the below line
# Squid normally listens to port 3128
http_port 3128
and replace with
# Squid normally listens to port 3128
http_port 3128 intercept
Step 2:- Create a file "/root/squidfw.sh" and add the following firewall script ( modify as per your interface configuration ).
#!/bin/sh
# squid server IP
SQUID_SERVER="192.168.1.11"
# 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 $LAN_IN -j ACCEPT
# DNAT port 80 request comming from LAN systems to squid 3128 ($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
Step 3:- just run the script
[root@hackthesec ~]# sh /root/squidfw.sh
and add the below line to "/etc/rc.local" to run the script during startup
sh /root/squidfw.sh

Step 4 (Updated):- Change default gateway ip to squid server ip on the user machines 
Now users can access Internet without setting proxy in the browser settings.

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