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Module 2: Single-Area OSPF (Overview)

Overview

The two main classes of IGPs are distance vector and link-state. Both types of routing protocols find routes through autonomous systems. Distance vector and link-state routing protocols use different methods to accomplish the same tasks.
Link-state routing algorithms, also known as shortest path first (SPF) algorithms, maintain a complex database of topology information. A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. In contrast, distance vector algorithms provide nonspecific information about distant networks and no knowledge of distant routers.
It is important to understand how link-state routing protocols operate in order to configure, verify, and troubleshoot them. This module explains how link-state routing protocols work, outlines their features, describes the algorithm they use, and points out the advantages and disadvantages of link-state routing.
Early routing protocols such as RIP v1 were all distance vector protocols. There are many distance vector routing protocols in use today such as RIP v2, IGRP, and the hybrid routing protocol EIGRP. As networks have grown larger and more complex, the limitations of distance vector routing protocols have become apparent. Routers that use a distance vector routing protocol learn about the network topology from the routing table updates of neighbor routers. Bandwidth usage is high because of the periodic exchange of routing updates, and network convergence is slow which results in poor routing decisions.
Link-state routing protocols differ from distance vector protocols. Link-state protocols flood route information, which allows every router to have a complete view of the network topology. Triggered updates allow efficient use of bandwidth and faster convergence. Changes in the state of a link are sent to all routers in the network as soon as the change occurs.
OSPF is one of the most important link-state protocols. OSPF is based on open standards, which means it can be developed and improved by multiple vendors. It is a complex protocol that is a challenge to implement in a large network. The basics of OSPF are covered in this module.
OSPF configuration on a Cisco router is similar to the configuration of other routing protocols. Similarly, OSPF must be enabled on a router and the networks that will be advertised by OSPF must be identified. OSPF has a number of features and configuration procedures that are unique. These features make OSPF a powerful choice for a routing protocol, but also make it a challenge to configure.
In large networks, OSPF can be configured to span many areas and several different area types. The ability to design and implement large OSPF networks begins with the ability to configure OSPF in a single area. This module also discusses the configuration of single-area OSPF.
This module covers some of the objectives for the CCNA 640-801 and ICND 640-811 exams. 
Students who complete this module should be able to perform the following tasks: 
  • Identify key link-state routing protocol features
  • Explain how link-state routing information is maintained
  • Discuss the link-state routing algorithm
  • Examine the advantages and disadvantages of link-state routing protocols
  • Compare and contrast link-state routing protocols with distance vector routing protocols
  • Enable OSPF on a router
  • Configure a loopback address to set router priority
  • Modify the cost metric to change OSPF route preference
  • Configure OSPF authentication
  • Change OSPF timers
  • Describe the steps to create and propagate a default route
  • Use show commands to verify OSPF operation
  • Configure the OSPF routing process
  • Define key OSPF terms
  • Describe the OSPF network types
  • Describe the OSPF Hello protocol
Identify the basics steps in the operation of OSPF

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