Transparent web proxy

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Revision as of 02:05, 15 February 2007

Running a transparent proxy server on your network can be used for more advanced content filtering of web pages for environments such as a school or library (where in some locales, filtering is required by law) or as a way to protect children in the household.

This guide will help you enable a transparent proxy server on your network by having your WRT54G router forward all traffic to the proxy server automatically.

Desktop Setup

First install Squid on your unix box after that you have to set up squid to do transparent proxying with these settings

httpd_accel_host virtual
httpd_accel_port 80

httpd_accel_with_proxy on

httpd_accel_uses_host_header on

Router Setup

You will need to use iptables to tell your router how to forward traffic. If you don't have a good grasp on iptables yet, someone has already done the work and written a shellscript to do the work for you. Be sure to edit the variables at the top.

The script can be found at:

if [ -z $TRANSPARENT_PROXY ]; then
  /usr/sbin/iptables -t nat -A PREROUTING -i br0 -s $INTERNAL_NETWORK \
    -d $INTERNAL_NETWORK -p tcp --dport 80 -j ACCEPT
  /usr/sbin/iptables -t nat -A PREROUTING -i br0 -s ! $PROXY_SERVER -p tcp --dport 80 \
  /usr/sbin/iptables -t nat -A POSTROUTING -o br0 -s $INTERNAL_NETWORK -p tcp -d \
  /usr/sbin/iptables -t filter -I FORWARD -s $INTERNAL_NETWORK -d $PROXY_SERVER -i br0 \
    -o br0 -p tcp --dport $PROXY_PORT -j ACCEPT
  echo "This script has already run!"
  echo "If it hasn't, unset \$TRANSPARENT_PROXY manually via the shell."

You'll need to have the script run every time the router boots. An easy way to do is to set as in the rc_firewall variable:

  1. Load the script in your text editor and set the variables accordingly.
  2. Then insert a backslash in front of each double-quote in the script so that they are escaped (otherwise they will cause an error when you perform the next step).
  3. From either Telnet/SSH_and_the_Command_Line:
# nvram set rc_firewall="
# nvram commit

You can confirm that the changes were made by executing

# nvram get rc_firewall

With some Squid installations, the proxy server may be expecting connections on an alternate port than the default of 3128. If this is the case, try changing the PROXY_PORT variable in the script above to the correct listening port, as in: