Configuring OSPF with Multiple Areas

In this lab, I use three Cisco 3725 routers [IOS 12.4(15)T10] to demonstrate how to setup OSPF with multiple Areas. Below is the network diagram for this lab.

Lab Diagram

Setup basic configuration on all routers:

R1

– enable
– configure terminal
– interface fastEthernet 0/0
– ip address 14.0.0.1 255.255.255.0
– no shutdown
– exit
– interface serial 0/0
– ip address 12.0.0.1 255.255.255.252
– no shutown
– exit
– interface loopback 1
– ip address 1.1.1.1 255.255.255.255
– exit
– exit
– write

R2

– enable
– configure terminal
– interface serial 0/0
– ip address 12.0.0.2 255.255.255.252
– no shutdown
– interface serial 0/1
– ip address 13.0.0.1 255.255.255.252
– no shutdown
– exit
– interface loopback 2
– ip address 2.2.2.2 255.255.255.255
– exit
– exit
– write

R3

– enable
– configure terminal
– interface serial 0/0
– ip address 13.0.0.2 255.255.255.252
– no shutdown
– interface fastEthernet 0/0
– ip address 15.0.0.1 255.255.255.0
– no shutdown
– exit
– interface loopback 3
– ip address 3.3.3.3 255.255.255.255
– exit
– exit
– write

Setup OSPF on all routers:

R1

– enable
– configure terminal
– router ospf 1
– network 12.0.0.0 0.0.0.3 area 1
– network 14.0.0.0 0.0.0.255 area 1
– network 1.1.1.1 0.0.0.0 area 1
– exit
– exit
– write

R2

– enable
– configure terminal
– router ospf 2
– network 12.0.0.0 0.0.0.3 area 1
– network 13.0.0.0 0.0.0.3 area 0
– network 2.2.2.2 0.0.0.0 area 0
– exit
– exit
– write

R3

– enable
– configure terminal
– router ospf 3
– network 13.0.0.0 0.0.0.3 area 0
– network 15.0.0.0 0.0.0.255 area 0
– network 3.3.3.3 0.0.0.0 area 0
– exit
– exit
– write

Below are some useful OSPF commands that can be used for troubleshooting/verification.

OSPF Ping Test From R1:

OSPF Ping Test

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Verification from R2:

show ip ospf interface brief

show ip ospf interface brief

show ip protocols

show ip protocols

show ip ospf neighbor

show ip ospf neighbor

An Area Border Router (ABR) is a router that belongs to two areas; it creates a summary of the prefixes in one area and announces it to the other area as a LSA Type 3. In every LSA Type 3, the ABR router puts itself as next-hop for the route. In the below output, you can see R2 is generating the LSA Type 3 packets respectively for R1 and R3.

show ip ospf database

show ip ospf database

show ip route

show ip route