===== Ubuntu Transparent Proxy =====

First up set up a box with 2 network cards installed, install Ubuntu Server onto it, and assign the network cards with static IP address.

Install squid sudo apt-get install squid and edit the /etc/squid/squid.conf file to your taste. Once you have squid working just how you like it, make sure the following directives are included:

<code>httpd_accel_host virtual
httpd_accel_port 80
httpd_accel_with_proxy on
httpd_accel_uses_host_header on</code>

Now create a file called proxy.sh - I got this script from an [[http://www.cyberciti.biz/tips/linux-setup-transparent-proxy-squid-howto.html|excellent Red Hat Linux tutorial]] 

You just need to edit the top bits labelled SQUID_SERVER, INTERNET, LAN_IN and SQUID_PORT.

<code>#!/bin/sh
# squid server IP
SQUID_SERVER=“192.168.1.1″
# 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</code>

Move script to /etc/init.d - Make it executable sudo chmod a+x proxy.sh and test it /etc/init.d/proxy.sh by setting the internet facing port as the gateway on a client machine.

Visit a few websites on the client machine, and see if they’re appearing in your squid access log tail /var/log/squid/access.log

To make sure your firewall rules work after a reboot, set your script to run during the startup process by making a symbolic link to the rc2.d directory ln -s /etc/init.d/proxy.sh /etc/rc2.d/S95proxy

Now if you change the gateway address the DHCP server gives to wireless clients ([[publicwifi:dhcpd.conf|the config file here]] if you're setting up [[publicwifi:public_wireless_internet_access|WiFiDog using the tutorial here]]), to the interface assigned to your LAN on the proxy, all traffic to port 80 will pass through your squid box thus being logged.