CHAPTER
21-1
Cisco ASA 5500 Series Configuration Guide using ASDM
OL-20339-01
21
Configuring OSPF
This chapter describes how to configure the adaptive security appliance to route data, perform
authentication, and redistribute routing information, using the Open Shortest Path First (OSPF) routing
protocol.
The chapter includes the following sections:
• Information About OSPF, page 21-1
• Licensing Requirements for OSPF, page 21-3
• Guidelines and Limitations, page 21-3
• Configuring OSPF, page 21-3
• Customizing OSPF, page 21-4
• Monitoring OSPF, page 21-20
• Configuration Example for OSPF, page 21-19
• Feature History for OSPF, page 21-21
Information About OSPF
OSPF is an interior gateway routing protocol that uses link states rather than distance vectors for path
selection. OSPF propagates link-state advertisements rather than routing table updates. Because only
LSAs are exchanged instead of the entire routing tables, OSPF networks converge more quickly than RIP
networks.
OSPF uses a link-state algorithm to build and calculate the shortest path to all known destinations. Each
router in an OSPF area contains an identical link-state database, which is a list of each of the router
usable interfaces and reachable neighbors.
The advantages of OSPF over RIP include the following:
• OSPF link-state database updates are sent less frequently than RIP updates, and the link-state
database is updated instantly rather than gradually as stale information is timed out.
• Routing decisions are based on cost, which is an indication of the overhead required to send packets
across a certain interface. The adaptive security appliance calculates the cost of an interface based
on link bandwidth rather than the number of hops to the destination. The cost can be configured to
specify preferred paths.
The disadvantage of shortest path first algorithms is that they require a lot of CPU cycles and memory.
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