OSPF Multi-Area

OSPF is a hierarchical because it allows the configuration of multi-areas. Having a layer approach does benefit an organization by having more efficient and concise routing tables, less SPF recalculations and less LSU and LSA traffic. Areas can retain problem from spreading across the enterprise. Below I configured OSPF on each router with their respect areas.

In this frame relay topology, the hub is the only DR and the spokes have been manually remove from the election process.

R1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/DROTHER    00:01:53    172.12.123.2    Serial0/0
3.3.3.3           0   FULL/DROTHER    00:01:43    172.12.123.3    Serial0/0

Here is some more useful information about the setup. I can see that the network type is non-broadcast, that R1 is the DR, the timer intervals are set at default .

R1#show ip ospf interface

Serial0/0 is up, line protocol is up

  Internet Address 172.12.123.1/24, Area 0

  Process ID 1, Router ID 1.1.1.1, Network Type NON_BROADCAST, Cost: 64

  Transmit Delay is 1 sec, State DR, Priority 1

  Designated Router (ID) 1.1.1.1, Interface address 172.12.123.1

  No backup designated router on this network

  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

    oob-resync timeout 120

    Hello due in 00:00:29

  Index 1/1, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 3

  Last flood scan time is 0 msec, maximum is 4 msec

  Neighbor Count is 2, Adjacent neighbor count is 2

    Adjacent with neighbor 2.2.2.2

    Adjacent with neighbor 3.3.3.3

  Suppress hello for 0 neighbor(s)

Loopback0 is up, line protocol is up

  Internet Address 1.1.1.1/32, Area 1

  Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1

  Loopback interface is treated as a stub Host

IP routes with the O IA  label are inter-area routes learned by OSPF.

R1#show ip route ospf
     2.0.0.0/32 is subnetted, 1 subnets
O IA    2.2.2.2 [110/65] via 172.12.123.2, 00:06:30, Serial0/0
     3.0.0.0/32 is subnetted, 1 subnets
O IA    3.3.3.3 [110/65] via 172.12.123.3, 00:06:30, Serial0/0