Categories R&S

OSPF – Building the topology – Configure OSPF areas

Let’s continue building our OSPF topology by configuring OSPF areas.

 

Requirements :

 

Configure OSPF area 2 and 3.

Make sure R4 is the DR router and R6 is the BDR for area 2.

Configure OSPF point-to-point network between R4-R1 and R4-R2.

Configure OSPF point-to-point network between R8-R1 and R9-R1.

Advertise Lo0 prefixes .

 

 

Diagram:

OSPF area

 

 

Configuring area 2:

 

I’m enabling OSPF between R4, R5 and R6 using the network command and set the priority at the interface level to manipulate the DR/BDR election process.

 

router ospf 10
network 10.10.2.0 0.0.0.255 area 2

R4(config)#int Ethernet1/0
R4(config-if)#ip ospf prio 255

R6(config)#int Ethernet0/0
R6(config-if)#ip ospf prio 254

R5(config)#int Ethernet0/0
R5(config-if)#ip ospf prio 0

 

Let’s verify that our adjacencies are UP between those 3 routers and that DR election is ok.

R4#sh ip ospf neigh
Neighbor ID     Pri   State           Dead Time   Address         Interface
55.55.55.55       0   FULL/DROTHER    00:00:39    10.10.2.5       Ethernet1/0
66.66.66.66     254   FULL/BDR        00:00:38    10.10.2.6       Ethernet1/0

 

I’m also advertising Lo0 and Lo1 into area 2.

 

Connecting area 2 to the backbone area:

 

As you can see in the diagram, we have two links to connect to the backbone area.

R4(config)#int Ethernet0/0
R4(config-if)#ip ospf 10 area 2

R4(config-if)#int Ethernet0/1
R4(config-if)#ip ospf 10 area 2

R1(config)#int Ethernet1/0
R1(config-if)#ip ospf 10 area 2

You have to manually configure the network type otherwise it will be defaulted to broadcast network.

 

Ethernet1/0 is up, line protocol is up
  Internet Address 10.10.14.1/30, Area 2, Attached via Interface Enable
  Process ID 10, Router ID 11.11.11.11, Network Type BROADCAST, Cost: 10

R4(config-if)#ip ospf network point-to-point
R1(config-if)#ip ospf network point-to-point

Ethernet1/0 is up, line protocol is up
  Internet Address 10.10.14.1/30, Area 2, Attached via Interface Enable
  Process ID 10, Router ID 11.11.11.11, Network Type POINT_TO_POINT, Cost: 10

 

Same for R2.

 

We now have area 2 connected to the backbone area.

R1#    sh ip ospf int brief
Interface    PID   Area            IP Address/Mask    Cost  State Nbrs F/C
Lo0          10    0               1.1.1.1/32         1     LOOP  0/0
Lo1          10    0               11.11.11.11/24     1     P2P   0/0
Et0/0        10    0               10.10.1.1/24       10    DR    2/2
Et1/0        10    2               10.10.14.1/30      10    P2P   1/1

R2#sh ip ospf
 Routing Process "ospf 10" with ID 22.22.22.22
 Start time: 00:04:48.682, Time elapsed: 05:07:40.330
SNIP
    Area BACKBONE(0)
        Number of interfaces in this area is 3 (1 loopback)
        Area has no authentication
SNIP
    Area 2
        Number of interfaces in this area is 1
        Area has no authentication
SNIP

 

Configuring area 3:

 

I’m following the same step to configure area 3.

R8#sh ip ospf int brief
Interface    PID   Area            IP Address/Mask    Cost  State Nbrs F/C
Lo1          10    3               88.88.88.88/24     1     P2P   0/0
Lo0          10    3               8.8.8.8/32         1     LOOP  0/0
Et0/0        10    3               10.10.18.2/30      10    P2P   1/1
Et0/1        10    3               10.10.3.8/24       10    DR    2/2
R8#sh ip ospf neigh
Neighbor ID     Pri   State           Dead Time   Address         Interface
11.11.11.11       0   FULL/  -        00:00:35    10.10.18.1      Ethernet0/0
99.99.99.99       1   FULL/BDR        00:00:34    10.10.3.9       Ethernet0/1
100.100.100.100   1   FULL/DROTHER    00:00:35    10.10.3.10      Ethernet0/1

R9#sh ip ospf int brief
Interface    PID   Area            IP Address/Mask    Cost  State Nbrs F/C
Lo0          10    3               9.9.9.9/32         1     LOOP  0/0
Lo1          10    3               99.99.99.99/24     1     P2P   0/0
Et0/0        10    3               10.10.39.2/30      10    P2P   1/1
Et0/1        10    3               10.10.3.9/24       10    BDR   2/2
R9#sh ip ospf neigh
Neighbor ID     Pri   State           Dead Time   Address         Interface
33.33.33.33       0   FULL/  -        00:00:35    10.10.39.1      Ethernet0/0
88.88.88.88       1   FULL/DR         00:00:36    10.10.3.8       Ethernet0/1
100.100.100.100   1   FULL/DROTHER    00:00:37    10.10.3.10      Ethernet0/1

 

We have now fulfill all the requirements.

 

As you can see R5 routing table is getting all the routes from the different areas.

 

R5#sh ip route ospf
Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/21] via 10.10.2.4, 00:38:49, Ethernet0/0
      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/21] via 10.10.2.4, 00:37:52, Ethernet0/0
      3.0.0.0/32 is subnetted, 1 subnets
O IA     3.3.3.3 [110/31] via 10.10.2.4, 00:37:52, Ethernet0/0
      4.0.0.0/32 is subnetted, 1 subnets
O        4.4.4.4 [110/11] via 10.10.2.4, 00:06:58, Ethernet0/0
      6.0.0.0/32 is subnetted, 1 subnets
O        6.6.6.6 [110/11] via 10.10.2.6, 00:05:59, Ethernet0/0
      8.0.0.0/32 is subnetted, 1 subnets
O IA     8.8.8.8 [110/31] via 10.10.2.4, 00:02:50, Ethernet0/0
      9.0.0.0/32 is subnetted, 1 subnets
O IA     9.9.9.9 [110/41] via 10.10.2.4, 00:02:18, Ethernet0/0
      10.0.0.0/8 is variably subnetted, 9 subnets, 3 masks
O IA     10.10.1.0/24 [110/30] via 10.10.2.4, 00:37:52, Ethernet0/0
O IA     10.10.3.0/24 [110/40] via 10.10.2.4, 00:02:50, Ethernet0/0
O IA     10.10.10.10/32 [110/41] via 10.10.2.4, 00:01:55, Ethernet0/0
O        10.10.14.0/30 [110/20] via 10.10.2.4, 00:41:50, Ethernet0/0
O IA     10.10.18.0/30 [110/30] via 10.10.2.4, 00:04:42, Ethernet0/0
O        10.10.24.0/30 [110/20] via 10.10.2.4, 00:41:40, Ethernet0/0
O IA     10.10.39.0/30 [110/40] via 10.10.2.4, 00:04:07, Ethernet0/0
      11.0.0.0/24 is subnetted, 1 subnets
O IA     11.11.11.0 [110/21] via 10.10.2.4, 00:38:49, Ethernet0/0
      22.0.0.0/24 is subnetted, 1 subnets
O IA     22.22.22.0 [110/21] via 10.10.2.4, 00:37:52, Ethernet0/0
      33.0.0.0/24 is subnetted, 1 subnets
O IA     33.33.33.0 [110/31] via 10.10.2.4, 00:37:52, Ethernet0/0
      44.0.0.0/24 is subnetted, 1 subnets
O        44.44.44.0 [110/11] via 10.10.2.4, 00:06:48, Ethernet0/0
      66.0.0.0/24 is subnetted, 1 subnets
O        66.66.66.0 [110/11] via 10.10.2.6, 00:05:59, Ethernet0/0
      88.0.0.0/24 is subnetted, 1 subnets
O IA     88.88.88.0 [110/31] via 10.10.2.4, 00:02:50, Ethernet0/0
      99.0.0.0/24 is subnetted, 1 subnets
O IA     99.99.99.0 [110/41] via 10.10.2.4, 00:02:18, Ethernet0/0
      100.0.0.0/24 is subnetted, 1 subnets
O IA     100.100.100.0 [110/41] via 10.10.2.4, 00:01:55, Ethernet0/0

 

I will keep working to finalize the topology in the next posts.

 

 

Thank you for reading.

 

OSPF – Building the topology – Configure OSPF areas