transparent proxy for squid in bridge configuration

Squid Config Example
Fully Transparent With TPROXY

Linux: Setup a transparent proxy with Squid in three easy steps

Squid Cache, TProxy, dan Mikrotik (Alternate Configuration for Simple Networks)

Configuring a Transparent Proxy/Webcache in a Bridge using Squid and ebtables

Squid 2.6 + tproxy + bridge + gentoo

To configure a bridge interface

ifconfig eth0 0.0.0.0 promisc up
ifconfig eth1 0.0.0.0 promisc up

brctl addbr br0
brctl addif br0 eth0
brctl addif br0 eth1

ifconfig br0 200.1.2.3 netmask 255.255.255.0 up
route add default gw 200.1.2.254 dev br0

To intercept the concerned connections:

bash# ebtables -t broute -A BROUTING -p IPv4 --ip-protocol 6 \
        --ip-destination-port 80 -j redirect --redirect-target ACCEPT

bash# iptables -t nat -A PREROUTING -i br0 -p tcp --dport 80 \
        -j REDIRECT --to-port 3128

The first command says that packets passing through the bridge going to port 80 will be redirected to the local machine, instead of being bridged. The second uses iptables to redirect those packets to local port 3128, so squid can take care of them.