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2. OSPF Link-State Routing & Area Topologies
Open Shortest Path First (OSPF) & Dijkstra Algorithm
OSPF is an Interior Gateway Protocol (IGP) operating inside an Autonomous System. It uses Dijkstra's Shortest Path First (SPF) algorithm to calculate loop-free topology maps from Link-State Advertisements (LSAs).
OSPF networks are organized into Areas, where Area 0 (Backbone Area) acts as the central hub connecting all other non-backbone areas.
Security Operator Note: Enable MD5 or HMAC-SHA256 authentication on OSPF interfaces to prevent unauthorized routers from poisoning the LSA database.
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# Inspecting OSPF neighbor status on Linux via Vtysh/FRR vtysh -c 'show ip ospf neighbor'
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