Router 1
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface FastEthernet0/0
Router(config-if)#ip add 172.16.3.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#interface Serial2/0
Router(config-if)#ip add 172.16.2.1 255.255.255.0
Router(config-if)#clock rate 9600
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#ip route 0.0.0.0 0.0.0.0 serial 2/0
Router 2
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface FastEthernet0/0
Router(config-if)#ip add 172.16.1.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#interface Serial2/0
Router(config-if)#ip add 172.16.2.2 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#interface Serial3/0
Router(config-if)#ip add 192.168.1.1 255.255.255.0
Router(config-if)#clock rate 9600
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#ip route 172.16.3.0 255.255.255.0 serial 2/0
Router(config)#ip route 192.168.2.0 255.255.255.0 serial 3/0
Router 3
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface FastEthernet0/0
Router(config-if)#ip add 192.168.2.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#
Router(config)#interface Serial2/0
Router(config-if)#ip add 192.168.1.2 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#ip route 172.16.0.0 255.255.252.0 serial 3/0
PC1
Ip address 172.16.3.2
Subnet mask 255.255.255.0
Default gateway 172.16.3.1
PC2
Ip address 172.16.1.2
Subnet mask 255.255.255.0
Default gateway 172.16.1.1
PC3
Ip address 192.168.2.2
Subnet mask 255.255.255.0
Default gateway 192.168.2.1