OSPF

EIGRP vs OSPF in 2026. The technical differences, the convergence story, vendor reality (EIGRP is still Cisco-only in practice), and the design implications for new vs existing networks.

BGP and OSPF solve different problems and almost always run together in production. The technical differences, when each is the right answer, and the architecture pattern most enterprises end up with.

On multi-access OSPF networks, the DR and BDR centralize LSA exchange so routers do not flood 45 sessions across 10 neighbors. A practical guide to what the DR and BDR do and why OSPF design depends on them.

Put 200 routers in one OSPF area and SPF, LSDB size, and flooding all break down. Areas fix scalability by isolating LSAs, SPF runs, and flooding. A plain-English guide to OSPF area design and why Area 0 is special.

OSPF neighbors progress through 8 states from Down to Full, and understanding the packet exchange at each step is the key to troubleshooting adjacency problems. A guide to OSPF neighbor states with real packet captures.

Router IDs, ABRs, ASBRs, stub areas, LSAs, costs, and adjacencies: the OSPF vocabulary is large. A plain-English reference to the key terms and concepts every network engineer working with OSPF should know.