When an OSPF router detects a broken link, it sends out an LSA (Link State Advertisement) informing all other routers of the failed link. This LSA is flooded throughout the OSPF network, so that all routers can update their OSPF topology database to reflect the change.
Each router then recalculates the shortest path tree (SPT) to all destinations based on the updated topology database. The new SPT is used to update the router’s forwarding table, so that packets are directed to the appropriate next-hop router.
If a router has alternate paths to a destination, it may switch its forwarding to one of these alternate paths to avoid the failed link. This process of recalculating the SPT and updating forwarding tables is done automatically by OSPF, ensuring that traffic is rerouted as quickly as possible in the event of a link failure.
