Establishing OSPF Neighbor Adjacency and Synchronizing Network Topology and Routing Information

What happens immediately after two OSPF routers have exchanged hello packets and have formed a neighbor adjacency?

After two OSPF routers have exchanged hello packets and formed a neighbor adjacency, the following steps occur:

1. Database Exchange: The routers exchange their link-state databases, which contain information about the network topology, reachable networks, and router capabilities.

2. Database Synchronization: The routers compare their link-state databases and synchronize them. This ensures that both routers have the same view of the network topology.

3. Designated Router (DR) and Backup Designated Router (BDR) Election: If the routers are in a multi-access network (such as Ethernet), they participate in a DR and BDR election process. The DR and BDR are responsible for maintaining neighbor adjacencies and exchanging routing updates with other routers in the network.

4. Link-State Advertisement (LSA) Generation and Flooding: Each router generates LSAs based on its own link-state database. These LSAs contain information about the router’s connected networks and reachability. The LSAs are then flooded throughout the OSPF network to inform all routers about the network’s topology.

5. Shortest Path First (SPF) Calculation: Once the LSAs have been flooded, each router independently runs a SPF algorithm to calculate the shortest path to each network in the OSPF domain. The SPF algorithm uses the link-state database and the cost associated with each link.

6. Routing Table Update: Based on the SPF calculation, each router updates its routing table to reflect the shortest paths to reach networks within the OSPF domain.

Overall, the OSPF routers go through a series of steps to establish neighbor adjacency and ensure the network topology and routing information are synchronized. This enables efficient routing and communication within the OSPF domain.

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