CCNA 新版（英文）D20S05L07.pps

© 2002, Cisco Systems, Inc. All rights reserved.
© 2002, Cisco Systems, Inc. All rights reserved.
2
Enabling OSPF
Objectives
pleting this lesson, you will be able to:
Describe the features and operation of OSPF
Use Cisco mands to configure dynamic routing for a single area work, given a functioning router
Use show and mands to identify anomalies in dynamic routing operation using OSPF, given an operational router
Introducing OSPF
Open standard
Shortest path first (SPF) algorithm
Link-state routing protocol (vs. distance vector)
OSPF as a Link-State Protocol
OSPF propagates link-state advertisements rather than routing table updates.
LSAs are flooded to all OSPF routers in the area.
The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers.
OSPF uses the SPF algorithm to calculate the shortest path to a destination.
Link = router interface
State = description of an interface and its relationship to neighboring routers
OSPF Hierarchical Routing
Consists of areas and autonomous systems
Minimizes routing update traffic
Shortest Path First Algorithm
Places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost
Cost = 108/bandwidth (bps)
Configuring Single Area OSPF
Router(config-router)#network address mask area area-id
works to a specific OSPF area
Router(config)#router ospf process-id
Defines OSPF as the IP routing protocol
OSPF Configuration Example
Configuring Loopback Interfaces
Router ID:
Number by which the router is known to OSPF
Default: The highest IP address on an active interface at the moment of OSPF process startup
Can be overridden by a loopback interface: Highest IP address of any active loopback interface