Cisco ROUTE 2.0: Link-State Database and Optimizing OSPF Behavior

Course details

• OSPF as a link state protocol uses several different packets to exchange information about network topology between routers. These packets are called link-state advertisements and they describe the network topology in great detail. Each router stores the received LSA packets in the link-state database. After LSDBs are synced between the routers, OSPF uses the shortest path first algorithm to calculate the best routes. The best intra-area routes are calculated inpidually by each OSPF router. For the best interarea route calculation, the internal router must also rely on the best path information received from the ABRs. Scalability, improved CPU and memory utilization, and the ability to mix small routers with large routers are all the benefits of using proper route summarization techniques. A key feature of the OSPF protocol is the ability to summarize routes at area and AS boundaries. The OSPF protocol defines several special-case area types, including stub areas, totally stubby areas, and NSSAs. The purpose of all three types of stub areas is to inject default routes into an area so that external and summary LSAs are not flooded. Default routes reduce the routing table size, and also reduce the memory and the CPU utilization. OSPF injects a default route unconditionally or based on the presence of a default route inside the routing table. This course explains how OSPF builds the routing table. This course also defines different types of route summarization and describes the configuration commands for each type. The OSPF area types and the benefits of default routes are also described.
• start the course
• describe different LSA types
• describe functions of type 1 LSAs
• describe functions of type 2 LSAs
• describe functions of type 3 LSAs
• describe functions of type 4 LSAs
• describe functions of type 5 LSAs
• recognize LSA types in the LSBD
• recognize how OSPF maintains link-state sequence numbers
• recognize the procedure to synchronize LSDBs
• recognize the function of the DR in the synchronization process
• identify how OSPF uses the OSFP algorithm
• recognize how OSPF determines link costs to calculate the best paths
• recognize how OSPF determines the best paths in a multiarea AS
• identify the properties of OSPF route summarization
• identify features of interarea route summarization
• identify how summarization can be performed for extern