When SPF Runs
Triggers:
- New LSA received
- LSA ages out
- Link state changes
- OSPF process starts
Partial SPF: Only affected routes recalculated
Full SPF: Entire tree rebuilt
SPF Timers
router ospf 1
timers throttle spf 5000 10000 10000
Format: start hold max (milliseconds)
- Start: Delay before first SPF
- Hold: Min time between SPFs
- Max: Max wait between SPFs
Monitoring SPF
R1# show ip ospf | include SPF
SPF algorithm last executed 00:15:23.456 ago
SPF algorithm executed 8 times
Many SPF runs = unstable network
Summary
✅ LSDB — Link-state database (network map)
✅ SPF — Dijkstra's algorithm (calculates best paths)
✅ Triggers — Topology changes
✅ SPF timers — Control calculation frequency
Next: Route Summarization (Article 28)
Internal Links:
- ← LSA Types (Article 26)
- → Route Summarization (Article 28)
- → Design Best Practices (Article 30)