Transparent web proxy

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-__toc__ 
- 
-=Introduction= 
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. 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. 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=+= Desktop Setup =
First install Squid on your unix box First install Squid on your unix box
after that you have to set up squid to do transparent proxying with these settings after that you have to set up squid to do transparent proxying with these settings
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httpd_accel_uses_host_header on httpd_accel_uses_host_header on
-=Router Setup=+= 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. 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.

Revision as of 23:49, 2 October 2006

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: http://forum.bsr-clan.de/viewtopic.php?p=10177#10177

#!/bin/sh
INTERNAL_NETWORK="192.168.0.0/24"
ROUTER_IP="192.168.0.1"
PROXY_SERVER="192.168.0.10"
PROXY_PORT="3128"
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 \
    -j DNAT --to $PROXY_SERVER:$PROXY_PORT
  /usr/sbin/iptables -t nat -A POSTROUTING -o br0 -s $INTERNAL_NETWORK -p tcp -d \
    $PROXY_SERVER -j SNAT --to $ROUTER_IP
  /usr/sbin/iptables -t filter -I FORWARD -s $INTERNAL_NETWORK -d $PROXY_SERVER -i br0 \
    -o br0 -p tcp --dport $PROXY_PORT -j ACCEPT
  export TRANSPARENT_PROXY="1"
else
  echo "This script has already run!"
  echo "If it hasn't, unset \$TRANSPARENT_PROXY manually via the shell."
fi


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. From either Telnet/SSH_and_the_Command_Line

# nvram set rc_firewall="
PASTE
EDITED 
SCRIPT
HERE
"
# nvram commit


You can confirm that the changes were made by executing

# nvram get rc_firewall

There is an error in trying to paste that script into the dd-wrt nvram. However here is a method that does work. Take the iptables part

  /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 \
    -j DNAT --to $PROXY_SERVER:$PROXY_PORT
  /usr/sbin/iptables -t nat -A POSTROUTING -o br0 -s $INTERNAL_NETWORK -p tcp -d \
    $PROXY_SERVER -j SNAT --to $ROUTER_IP
  /usr/sbin/iptables -t filter -I FORWARD -s $INTERNAL_NETWORK -d $PROXY_SERVER -i br0 \
    -o br0 -p tcp --dport $PROXY_PORT -j ACCEPT

and replace the variables with the right information : i.e. $INTERNAL_NETWORK, $PROXY_SERVER, $PROXY_PORT, and $ROUTER_IP. Once that is done, just copy and paste those three lines where you were trying to paste that whole script.. don't for get the " at the end on a line by itself.

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:

PROXY_PORT="8080"