Which Fields Must Match in OSPF Hello Packet?

BCD

OSPF (Open Shortest Path First) is a routing protocol used to exchange routing information within a single autonomous system (AS). It is designed to operate within a larger network and uses a hierarchical structure to reduce the size of the routing table and improve network efficiency.

When OSPF is configured on two routers over a point-to-point link, certain fields in the OSPF hello packet must match to establish and maintain neighbor adjacency. These fields include:

1. Network mask: This field specifies the subnet mask used by both routers on the point-to-point link. The subnet mask must be identical on both routers for neighbor adjacency to be established.

2. Hello interval: This field specifies the time interval at which OSPF hello packets are sent between the two routers. The hello interval must be the same on both routers for neighbor adjacency to be established.

3. Dead interval: This field specifies the time interval after which a router declares a neighboring router to be dead if it does not receive hello packets from the neighbor. The dead interval must be the same on both routers for neighbor adjacency to be maintained.

Other fields in the OSPF hello packet that do not need to match include:

1. Options: This field contains various flags that control the behavior of OSPF. The options field does not need to match between routers for neighbor adjacency to be established.

2. Backup designated router: This field identifies the router that will take over as designated router (DR) if the current DR fails. The backup designated router does not need to match between routers for neighbor adjacency to be established.

In summary, when deploying OSPF between two routers over a point-to-point link, the network mask, hello interval, and dead interval fields in the OSPF hello packet must match for neighbor adjacency to be established and maintained.