An enterprise router configured with OSPF receives a Link-State Update (LSU) packet containing a newer Link-State Advertisement (LSA) for a remote network segment. In what chronological order does the router process this update from initial receipt to global RIB installation?
- 1Validate the incoming LSU packet and confirm that the contained LSA sequence number is higher than the existing entry in the local LSDB.
- 2Update the local Link-State Database (LSDB) and flood the LSU packet out all active OSPF-enabled interfaces except the receiving interface.
- 3Run Dijkstra's Shortest Path First (SPF) algorithm on the updated LSDB topology map.
- 4Calculate new cumulative metric path costs and update the protocol-specific OSPF routing table.
- 5Offer the candidate route to the global Routing Information Base (RIB), evaluating Administrative Distance against competing protocol routes.
Answer
The correct sequence for processing an incoming OSPF LSU is: 1) Validate the incoming LSU packet and confirm a higher LSA sequence number; 2) Update the local LSDB and flood the LSU out active OSPF interfaces; 3) Run Dijkstra's Shortest Path First (SPF) algorithm; 4) Calculate new cumulative path costs and update the internal OSPF routing table; 5) Offer the candidate route to the global Routing Information Base (RIB) using Administrative Distance.
Upon receiving an LSU, the router verifies that the LSA sequence number is newer than its existing LSDB record. It then updates the LSDB and immediately floods the update out other interfaces to propagate the change across the OSPF area. Next, the router executes the SPF calculation to build an updated shortest-path tree, calculates cumulative metric path costs for OSPF routing, and finally submits the route to the global RIB where Administrative Distance comparison determines final forwarding entry installation.
Step-by-Step Solution
Key Concept
OSPF Link-State Processing and Convergence Sequence