OSPF - Routing Protocols and Concepts - page 500

OSPF Algorithm

Each OSPF router maintains a link - state database containing the LSAs received from all other routers.
After a router has received all LSAs and built its local link - state database , OSPF uses Dijkstra's short-
est path first ( SPF ) algorithm to create an SPF tree. The SPF tree is then used to populate the IP rout-
ing table with the best paths to each network.

Administrative Distance

With this chapter, you have learned all the administrative distances for the routing protocols covered on
the CCNA exam. Fill in the missing route sources and administrative distance (AD) values in Table 11-1.

Table 11-1 Default Administrative Distances

Route Source AD

Connected 0

Static 1

EIGRP summary route 5

External BGP 20

Internal EIGRP 90

IGRP 100

OSPF 110

IS-IS 115

RIP 120

External EIGRP 170

Internal BGP 200

Basic OSPF Configuration

Now that you have a good understanding of how OSPF works, it is time to learn the configuration
commands you use for OSPF. The first exercise in the following sections will take you step by step
through an OSPF configuration. The second exercise reviews verification commands.

Learn the OSPF Commands Exercise

Document the command syntax, including the router prompt, to configure the OSPF routing
process.
Router(config)# router ospf process-id

1.

The value for process-id can be any number between 1 and 65,535 . 2.

True or False: All routers in an area must have the same process-id .

3.

False. The process-id is only significant to the local router and has no meaning to other OSPF neigh-
bors. OSPF neighbors are unaware of what process ID the local router is using. However, it is consid-
ered a best practice to maintain a consistent process ID throughout the routing domain.