Which event typically triggers a recalculation of SPF in OSPF?

Which event typically triggers a recalculation of SPF in OSPF?

• A. Regular timer every 60 seconds
• B. When a router becomes adjacent to a new neighbor
• C. Topology change or LSA update
• D. Only on startup

Answer: (C)

OSPF recalculates its shortest-path tree whenever the router’s view of the network changes. That view is stored in the link-state database, which is updated whenever new information arrives or existing information changes. When an LSA is received and the LSDB is updated, or when an adjacency change occurs (such as a neighbor becoming reachable or dropping out), the topology changes. This triggers a new SPF computation so the router can rebuild the shortest-path tree and refresh its routing table accordingly. There is typically a short SPF delay to batch multiple changes, but the essential trigger is the topology change or LSA update, not a fixed timer. The initial SPF runs at startup to build the initial topology, but ongoing recalculations happen after changes.

OSPF recalculates its shortest-path tree whenever the router’s view of the network changes. That view is stored in the link-state database, which is updated whenever new information arrives or existing information changes. When an LSA is received and the LSDB is updated, or when an adjacency change occurs (such as a neighbor becoming reachable or dropping out), the topology changes. This triggers a new SPF computation so the router can rebuild the shortest-path tree and refresh its routing table accordingly. There is typically a short SPF delay to batch multiple changes, but the essential trigger is the topology change or LSA update, not a fixed timer. The initial SPF runs at startup to build the initial topology, but ongoing recalculations happen after changes.