Open Shortest Path First, the link-state IGP behind most enterprise networks. Articles tagged OSPF cover neighbor relationships, LSA types, areas, DR/BDR election, and Cisco IOS XE configuration.
show ip ospf database prints five section headers and none of them says "Type 1". Here is every LSA type identified on real output from a three-router, two-area CML lab with an ASBR, on IOS XE 17.18.2, plus the route code each type ends up as.
On broadcast networks, mismatched subnet masks leave OSPF stuck in Init or 2-Way. Here is the fast diagnosis with show ip ospf neighbor and the one-line fix.
Real OSPF design rules: keep Area 0 stable and small, cap routers per area, use stub where you can, and make summarization a feature of your area boundaries.
Learn to configure and verify single-area OSPFv2 on Cisco routers with complete Router ID setup, network commands, and wildcard masks. Includes hands-on Cisco CML lab with full verification outputs and troubleshooting steps.
A complete single-area OSPF configuration on three Cisco routers, with every output block captured live from IOS XE 17.18: neighbors, routes, DR/BDR, ECMP, and the defaults worth changing.
OSPF uses five packet types (Hello, DBD, LSR, LSU, LSAck) to discover neighbors and sync the LSDB. Here is what each one does and where it fits in the adjacency process.
OSPF vs EIGRP, RIP, BGP, and IS-IS: how they differ on convergence, scalability, vendor support, and metric logic, and when OSPF is actually the right choice.
OSPF gives every router in an area an identical map and lets each compute its own shortest paths. How the LSDB, adjacencies, DR/BDR, cost, and areas actually fit together, with live captures.
OSPF is a link-state routing protocol that builds an LSDB, runs Dijkstra, and converges fast. Here is what problem it solves, how it works, and where it fits.