OSPF Multi-Area Configuration

The network is growing, and it is being reorganized into areas.
The senior network engineer sends you the plan:

Figure 1 - The network plan

All interfaces already have their IP addresses configured.
OSPF is already running on R1, R4, R5, and R6.

Your job is to configure the two routers that connect the areas together: R2 and R3.

When you are ready, mark this step as complete and continue.

Start the OSPF process, define a router ID, and when advertising networks, specify the correct area.

R2# conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# router ospf 1
R2(config-router)# router-id 2.2.2.2
R2(config-router)# network 10.1.12.0 0.0.0.3 area 1
R2(config-router)# network 10.0.23.0 0.0.0.3 area 0
R2(config-router)# end

R2 is connected to 10.1.12.0 in Area 1 and to 10.0.23.0 in Area 0.

Now move to R3, which connects Area 0 and Area 2.

R3# conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)# router ospf 1
R3(config-router)# router-id 3.3.3.3
R3(config-router)# network 10.0.23.0 0.0.0.3 area 0
R3(config-router)# network 10.2.34.0 0.0.0.3 area 2
R3(config-router)# end

Look at the messages on the screen.
Two neighbors reached FULL: R2 in Area 0, and R4 in Area 2.
All three areas are now connected.

Same routine as the last course: configure, then verify.
First, check that the interfaces of R2 belong to the correct areas.

R2# show ip ospf interface brief 
Interface    PID   Area            IP Address/Mask    Cost  State Nbrs F/C
Gi0/0        1     0               10.0.23.1/30       1     DR    1/1
Gi0/1        1     1               10.1.12.2/30       1     BDR   1/1

Each interface of R2 is in the correct area.
Now, check the routes learned by R2.

R2# show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O IA     10.2.34.0/30 [110/2] via 10.0.23.2, 00:04:04, GigabitEthernet0/0
O IA     10.2.100.0/24 [110/3] via 10.0.23.2, 00:04:03, GigabitEthernet0/0

R2 has learned the networks 10.2.34.0/30 and 10.2.100.0/24, which belong to Area 2.
From R2, the networks of Area 2 are reachable.

Notice that these routes are marked O IA, not O.
You will find out what IA means in the next course.