Listing 1. setup_network_connections.sh

###### create the br0 and br1 bridge with the brctl utility
brctl  addbr br0
brctl  addbr br1

##### delete all old configurations if they exist
ifconfig br0 0.0.0.0 down
brctl  delif br0 tap0
brctl  delif br0 tap1
ifconfig br1 0.0.0.0 down
brctl  delif br1 tap3
brctl  delif br1 tap4

##### flush all filter and nat rules
iptables -t nat -F
iptables  -F


##### turn on debug prints
set -x

####  make all tap interfaces up.
ifconfig tap0 0.0.0.0 up
ifconfig tap1 0.0.0.0 up
ifconfig tap3 0.0.0.0 up
ifconfig tap4 0.0.0.0 up

#### add tap0 and tap1 to br0 bridge
brctl addif br0 tap0
brctl addif br0 tap1

#### add tap3 and tap4 to br1 bridge
brctl addif br1 tap3
brctl addif br1 tap4

##### assign br0 with 192.168.10.1 ip and make it up
ifconfig br0 192.168.10.1 netmask 255.255.255.0    up

##### assign br1 with 192.168.30.1 ip and make it up
ifconfig br1 192.168.30.1 netmask 255.255.255.0    up

##### assign tap2 interface with 192.168.20.1 ip and make it up
ifconfig tap2 192.168.20.1  netmask 255.255.255.0  up

##### enable ip forward
echo 1 > /proc/sys/net/ipv4/ip_forward

##### make the default policy of the forward chain as accept
##### to avoid any possibility of dropping packets in filter chain
iptables -P FORWARD ACCEPT

##### add a NAT rule to Masquerade packets from uml-R to the host machine.
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE