Which statement about OSPF neighbor adjacencies is correct?
- The hello/dead timers, area IDs, and authentication information must match within the LSAck messages for two devices to form an OSPF neighbor relationship.
- Only the hello/dead timers and authentication information must match within the hello messages for two devices to form an OSPF neighbor relationship. Area IDs and router IDs must be unique.
- The hello/dead timers, area IDs, and authentication information must match within the hello messages for two devices to form an OSPF neighbor relationship.
- The hello/dead timers, area IDs, and router ID information must match within the hello messages for two devices to form an OSPF neighbor relationship.
- The hello/dead timers, area IDs, and authentication information must be unique within the DBD messages for two devices to form an OSPF neighbor relationship.
Explanation: OSPF routers use the Hello protocol to discover neighbors and establish adjacencies. For a neighbor relationship to form, routers must agree on specific parameters carried within their hello messages.
Specifically, the following information must match:
- Hello and Dead Intervals: These timers specify how often hello packets are sent and how long a router waits before declaring a neighbor down. If these are mismatched, an adjacency will not be established.
- Area ID: Neighbors must share a common segment and their interfaces must be assigned to the same OSPF area.
- Authentication Data: If authentication is enabled, both routers must use the same authentication type and exchange matching keys.
- Stub Area Flag: Routers must also agree on whether the area is a stub area.
In contrast, Router IDs must be unique for each router within an OSPF network to avoid identification issues and potential outages; they should not match between neighbors. Furthermore, these compatibility checks occur during the initial hello packet exchange, not within LSAck, DBD, or other subsequent packet types.
Related exam: Modules 8 – 13: Checkpoint Exam: Network Routing Answers (CCNP ENCOR v9)
