Simple Squid Filtering Proxy for Raspberry Pi

Back when it was announced, I ordered a Pi-Top Ceed with the intention of it being my daughter’s first computer. Awhile back the SD card failed, and I finally got around to fixing things.

One of the quick hacks I created when I first set this up was a local proxy server using Squid that used OpenDNS for content filtering. I’m an IT geek, so I want the computer to be able to use internal DNS to access other services I’m running on my home network but I also really don’t want to go deep into the woods on content filtering and setup setup (and maintain) things like Dan’s Guardian and SquidGuard.

If I do things the easy way and changed the Raspberry Pi’s DNS servers to OpenDNS the computer won’t be able to use my internal DNS names to find the network printer, file shares, and other services. That’s not going to work for me.

Squid has an option to use specific name servers instead of the system specified name servers when it proxies connections. This option paired with OpenDNS makes content filtering (as well as monitoring and reporting) very easy and lets the system use my internal DNS servers to find local services. Plus the configuration is very simple, add two lines to the default Squid configuration.

The Squid Configuration:

# Default configuration from https://wiki.squid-cache.org/Squid-4
 http_port 3128
# Example rule allowing access from your local networks.
# Adapt to list your (internal) IP networks from where browsing
# should be allowed
 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 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
 http_access deny !Safe_ports
 http_access deny !SSL_ports
 http_access allow localhost manager
 http_access deny manager
 #
 # INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
 #
 http_access allow localnet
 http_access allow localhost
 coredump_dir /squid/var/cache/squid
 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
 
 # No caching, proxy only. (No writing to the Pi's SD card.)
 cache deny all
 # Use OpenDNS for content filtering/blocking.
 dns_nameservers 208.67.222.222 208.67.220.220

From there, you just have to configure the OS to use the proxy, which is documented on the Raspberry Pi website.

OpenDNS uses your public IP to identify your network. If you don’t have a public IP make sure you setup a the OpenDNS Updater client somewhere. ddclient is available in Raspbian for this task as well.

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