OSPF Routing Protocol Summary

What Is OSPF?
• Open Shortest Path First
• Link State Protocol using the Shortest Path First algorithm (Dijkstra) to calculate loop-free routes
• Used purely within the TCP/IP environment
• Designed to respond quickly to topology changes but using minimal protocol traffic
• Used in both Enterprise and Service Provider Environment
• Uses IP protocol 89
• Metric is cost, based on interface bandwidth by default (10^8 / BW in bps)
• Sends partial route updates only when there are changes
• Send hello packets every 10 sec with dead timer of 40 sec over Point to Point & Broadcast networks
• Send hello packets every 30 sec with dead timer of 120 sec over NBMA networks
• Uses multicast address (ALL SPF Routers)
• Uses multicast address (ALL DR Routers)

Different Types of OSFP LSAs
1. Router Link State Advertisement (Type 1 LSA)
2. Network Link State Advertisement (Type 2 LSA)
3. Summary Link State Advertisement (Type 3 and Type 4 LSA)
4. External Link State Advertisement (Type 5 LSA)

Different types of OSPF Packet
1. Hello
2. Database description
3. Link State Request
4. Link State Update
5. Link State Acknowledgement


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