OSPF Area Types & Where Filtering Works

Area types control which LSAs are allowed, to shrink tables and speed convergence. All routers in an area must agree. Area LSAs allowed External ASBR inside CLI Normal 1,2,3,4,5 yes yes default Stub 1,2,3 no (5 blocked) + default from ABR no area X stub Totally stub (Cisco) 1,2 no, only default no area X […]

OSPF Core — LSAs, Timers, Router ID

Link-state IGP, metric = cost, Dijkstra (SPF), protocol 89, AD 110, multicast 224.0.0.5 / 224.0.0.6 (DR/BDR). Area 0 is the mandatory backbone. Router ID & DR election Router-ID: manual → highest loopback → highest active interface IP. DR election: highest priority (tie: highest RID). Hello/Dead must match between neighbors or no adjacency: 10/40 s on […]