OSPF

OSPF passive-interface stops Hellos and adjacencies on an interface but still advertises its subnet. Config, the default pattern, and the route-filter gotcha.

OSPF cost explained: the formula, the default reference bandwidth that breaks at 1 Gbps and above, manual overrides per interface, ECMP, and the misconfigurations to avoid.

All 8 OSPF neighbor states (Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, Full), what triggers each transition, and what to check when a neighbor is stuck.

When OSPF and BGP both know about the same prefix, who wins? A practical walkthrough of mutual redistribution, the admin-distance trap, and why BGP into OSPF needs a filter or it takes down your domain.

OSPF has a lot of moving parts. The state machine. The LSA types. The area types and what each one

Run OSPF, EIGRP, and BGP across GRE tunnels on Cisco IOS XE. Recursive routing fix, OSPF network types, EIGRP metric tuning, and BGP update-source.