A. Test topology:
Two. Basic configuration:
A.r1
Interface Loopback0
IP address 192.168.1.1 255.255.255.0
Interface fastethernet0/0
IP address 10.1.1.1 255.255.255.0
No shut
B.r2
Interface ethernet0/0
IP address 10.1.1.2 255.255.255.0
No shut
Interface ETHERNET0/1
IP address 202.100.1.2 255.255.255.0
No shut
C.r3
Interface fastethernet0/0
IP address 202.100.1.3 255.255.255.0
No shut
Interface FASTETHERNET0/1
IP address 202.100.2.3 255.255.255.0
No shut
D.r4
Interface ethernet0/0
IP address 20.1.1.4 255.255.255.0
No shut
Interface ETHERNET0/2
IP address 30.1.1.4 255.255.255.0
No shut
Interface ETHERNET0/1
IP address 202.100.2.4 255.255.255.0
No shut
E.r5
Interface Loopback0
IP address 192.168.2.5 255.255.255.0
Interface fastethernet0/0
IP address 20.1.1.5 255.255.255.0
No shut
F.r6
Interface Loopback0
IP address 192.168.3.6 255.255.255.0
Interface fastethernet0/0
IP address 30.1.1.6 255.255.255.0
No shut