cfg /etc/network/interfaces

auto lo
iface lo inet loopback

auto br0
iface br0 inet static
 address <ipv4 addr>
 netmask 255.255.255.0
 gateway <ipv4 addr>

pre-up tunctl -u root -t tap0
pre-up ifconfig eth0 0.0.0.0 promisc up
pre-up ifconfig tap0 0.0.0.0 promisc up
pre-up brctl addbr br0
pre-up brctl addif br0 eth0
pre-up brctl addif br0 tap0
post-down tunctl -d tap0
post-down brctl delbr br0

allow-hotplug eth0
iface eth0 inet manual
pre-up ifconfig eth0 0.0.0.0 promisc up
pre-up brctl addif br0 eth0
pre-down brctl delif br0 eth0
pre-down ifconfig eth0 down

bounce network interfaces

connect gns3 cloud to rtr