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Difficulty: HardOSPFv2 Neighbor Adjacencies and Router ID

Two Cisco routers, R1 and R2, are connected via their GigabitEthernet0/0 interfaces over a point-to-point Ethernet link. A network engineer notices that OSPFv2 fails to establish a neighbor relationship between them. The engineer issues verification commands on both routers and observes the following command outputs:

R1# show ip ospf interface gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.1.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

R2# show ip ospf interface gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.1.1.2/24, Area 10
Process ID 2, Router ID 2.2.2.2, Network Type BROADCAST
Timer intervals configured, Hello 15, Dead 60, Wait 60, Retransmit 5

Which TWO configuration changes will resolve the neighbor adjacency failure between R1 and R2? (Select TWO.)

  1. Reconfigure R2's interface so that its OSPF Area ID matches Area 0.Answer
  2. Adjust R2's Hello and Dead timers to 10 seconds and 40 seconds respectively to match R1.Answer
  3. C
    Change R2's OSPF Process ID from 2 to 1 so that both routers use identical process numbers.
  4. D
    Configure R2 with a Router ID of 1.1.1.1 to match R1's Router ID.

Answer

The two required configuration changes are: reconfiguring R2's interface so its OSPF Area ID matches Area 0, and adjusting R2's Hello and Dead timers to 10 seconds and 40 seconds to match R1.
To form an OSPFv2 neighbor adjacency over a connected link, routers must exchange Hello packets that agree on several mandatory fields. The Area ID (Area 0 vs Area 10) and the Hello/Dead timer intervals (10/40 vs 15/60) are mismatched in the output. Reconfiguring R2 to use Area 0 and setting its timers to Hello 10s / Dead 40s removes both blocking conditions, allowing neighbor adjacency to complete.

Step-by-Step Solution

1
Analyze the CLI output for OSPF Area ID configuration on both routers.
R1 is in Area 0 while R2 is in Area 10.
OSPF interfaces on the same subnet must belong to the exact same area for an adjacency to form.
2
Compare the configured OSPF Hello and Dead timer values between R1 and R2.
R1 has Hello 10s / Dead 40s, whereas R2 has Hello 15s / Dead 60s.
Mismatching Hello/Dead timers prevent OSPF routers from accepting Hello packets and forming a neighbor relationship.
3
Evaluate the non-matching parameters (Process ID and Router ID) to determine if they impact adjacency.
Process IDs do not need to match (local significance only), and Router IDs must remain unique rather than identical.
Only Area ID, Hello/Dead timers, Subnet Mask, MTU, and Authentication fields must satisfy adjacency checks in Hello exchanges.

Key Concept

OSPFv2 Neighbor Adjacency Requirements
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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