Developing a forward proxy server with Squid

cloudinfrastructurelinuxsquidproxy

Virtual Machine (Alma linux)

Initial configuration:

  • OS: Alma Linux 8.4

Squid is a proxy server that can be used as a forward or reverse proxy. In this project we are going to develop a forward proxy server with Squid.

Forward proxy server: The client knows that it is using a proxy server. We can complete this task following the next steps:

  1. Install squid
sudo dnf update -y
sudo dnf install squid -y

Note: The -y flag is to accept all the dependencies automatically

  1. Start the service and enable for start when the server (machine) starts. Also check the status of the service
systemctl start squid
systemctl enable squid
systemctl status squid
  1. Create a file for blocked domains in /etc/squid/ with .txt extension
touch /etc/squid/blocked_domains.txt
  1. Fill the created file with some domains to block
.facebook.com
.twitter.com
.youtube.com
.tiktok.com
.uta.edu
.ec
.io

Note: Also we can create a file to save blocked words in the URL

  1. Create a backup for the squid configuration file
cp /etc/squid/squid.conf /etc/squid/squid.conf.bak
  1. In the squid.conf put the following content
#
# Recommended minimum configuration:
#

# Example rule allowing access from your local networks.
# Adapt to list your (internal) IP networks from where browsing
# should be allowed

### Comment these lines

# acl localnet src 0.0.0.1-0.255.255.255	# RFC 1122 "this" network (LAN)
# acl localnet src 10.0.0.0/8		# RFC 1918 local private network (LAN)
# acl localnet src 100.64.0.0/10		# RFC 6598 shared address space (CGN)
# acl localnet src 169.254.0.0/16 	# RFC 3927 link-local (directly plugged) machines
# acl localnet src 172.16.0.0/12		# RFC 1918 local private network (LAN)
# acl localnet src 192.168.0.0/16		# RFC 1918 local private network (LAN)
# acl localnet src fc00::/7       	# RFC 4193 local private network range
# acl localnet src fe80::/10      	# RFC 4291 link-local (directly plugged) machines

acl bad_domains dstdomain "/etc/squid/blocked_domains.txt"
acl bad_words url_regex "etc/squid/blocked_words.txt" # for blocked words

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

#
# Recommended minimum Access Permission configuration:
#
# 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

# Only allow cachemgr access from localhost
http_access allow localhost manager
http_access deny manager

# 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

http_access deny bad_domains
http_access deny bad_words
http_access allow all

# Squid normally listens to port 3128
http_port 3128

# 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
  1. Disable the firewall and disable to start when the server starts
systemctl stop firewalld
systemctl disable firewalld
  1. Restart the squid service
systemctl restart squid
  1. Check the squid logs
tail -f /var/log/squid/access.log
  1. Configure the browser to use the proxy server
  • Go to the browser settings
  • Search for proxy settings
  • Put the IP address of the server and the port 3128
    • IP: You can know the IP address of the server with the command ip a
    • PORT: 3128 is the default port for squid

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