Transparent Layer 2 Bridge

sudo apt-get install bridge-utils

sudo brctl addbr br0

echo 8 | sudo tee -a /sys/class/net/br0/bridge/group_fwd_mask

sudo brctl addif br0 eth1

sudo brctl addif br0 eth2

sudo ifconfig eth1 up

sudo ifconfig eth2 up

sudo ifconfig br0 up