CCIE: OSPF
The Basics: Link state routing protocol. Uses IP protocol 89. Hellos sent on 224.0.0.5. Uses Dijkstra SPF algorithm independently on each router against the local LSDB to calculate the best routes. Hellos sent every 10 seconds on LAN and 30 seconds on WAN interfaces. Dead time is 4x hello, so 40sec and 120 sec respectively. Router ID: 1) Configured “router id” 2) Highest loopback 3) Highest non loopback interface in up/up state. Hello Process Sanity check: Pass authentication (verify with “debug ip ospf adj”)…