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Implementing OSPF for IPv4

Chapter Description

In this sample chapter fromCCNA Routing and Switching ICND2 200-105 Official Cert Guide, author Wendell Odom covers implementation details for Open Shortest Path First Version 2 (OSPFv2) —that is, OSPF as used for IPv4. This chapter looks at how to configure and verify a variety of OSPFv2 features

Chapter Review

One key to doing well on the exams is to perform repetitive spaced review sessions. Review this chapter’s material using either the tools in the book, DVD, or interactive tools for the same material found on the book’s companion website. Refer to the “Your Study Plan” element for more details. Table 8-5 outlines the key review elements and where you can find them. To better track your study progress, record when you completed these activities in the second column.

Table 8-5 Chapter Review Tracking

Review Element

Review Date(s)

Resource Used:

Review key topics


Book, DVD/website

Review key terms


Book, DVD/website

Answer DIKTA questions


Book, PCPT

Do labs



Review Config Checklists


Book, DVD/website

Review command tables



Review All the Key Topics


Table 8-6 Key Topics for Chapter 8

Key Topic Element


Page Number


Example OSPF wildcard masks and their meaning


Example 8-4

Example of the show ip ospf neighbor command



Rules for setting the router ID



Actions IOS takes when an OSPF interface is passive


Example 8-14

Example of a multiarea OSPFv2 configuration


Figure 8-5

Popular OSPF show commands and their general purposes


Example 8-15

Example of the show ip ospf interface brief showing interfaces in multiple areas


Figure 8-6

Actions taken by the OSPF default-information originate command



Rules for setting OSPF interface cost


Example 8-22

Differences in show ip ospf interface output with OSPF interface configuration


Key Terms You Should Know

  • reference bandwidth

  • interface bandwidth

  • maximum paths

Command References

Tables 8-7 and 8-8 list configuration and verification commands used in this chapter. As an easy review exercise, cover the left column in a table, read the right column, and try to recall the command without looking. Then repeat the exercise, covering the right column, and try to recall what the command does.

Table 8-7 Chapter 8 Configuration Command Reference



router ospf process-id

Enters OSPF configuration mode for the listed process.

network ip-address wildcardmask area area-id

Router subcommand that enables OSPF on interfaces matching the address/wildcard combination and sets the OSPF area.

ip ospf process-id area area-number

Interface subcommand to enable OSPF on the interface and to assign the interface to a specific OSPF area.

ip ospf cost interface-cost

Interface subcommand that sets the OSPF cost associated with the interface.

bandwidth bandwidth

Interface subcommand that directly sets the interface bandwidth (Kbps).

auto-cost reference-bandwidth number

Router subcommand that tells OSPF the numerator in the Reference_bandwidth / Interface_bandwidth formula used to calculate the OSPF cost based on the interface bandwidth.

router-id id

OSPF command that statically sets the router ID.

interface loopback number

Global command to create a loopback interface and to navigate to interface configuration mode for that interface.

maximum-paths number-of-paths

Router subcommand that defines the maximum number of equal-cost routes that can be added to the routing table.

passive-interface type number

Router subcommand that makes the interface passive to OSPF, meaning that the OSPF process will not form neighbor relationships with neighbors reachable on that interface.

passive-interface default

OSPF subcommand that changes the OSPF default for interfaces to be passive instead of active (not passive).

no passive-interface type number

OSPF subcommand that tells OSPF to be active (not passive) on that interface or subinterface.

default-information originate [always]

OSPF subcommand to tell OSPF to create and advertise an OSPF default route, as long as the router has some default route (or to always advertise a default, if the always option is configured).

Table 8-8 Chapter 8 EXEC Command Reference



show ip ospf

Lists information about the OSPF process running on the router, including the OSPF router ID, areas to which the router connects, and the number of interfaces in each area.

show ip ospf interface brief

Lists the interfaces on which the OSPF protocol is enabled (based on the network commands), including passive interfaces.

show ip ospf interface [type number]

Lists a long section of settings, status, and counters for OSPF operation on all interfaces, or on the listed interface,including the Hello and Dead Timers.

show ip protocols

Shows routing protocol parameters and current timer values.

show ip ospf neighbor [type number]

Lists brief output about neighbors, identified by neighbor router ID, including current state, with one line per neighbor;optionally, limits the output to neighbors on the listed interface.

show ip ospf neighbor neighbor-ID

Lists the same output as the show ip ospf neighbor detail command, but only for the listed neighbor (by neighbor RID).

show ip ospf database

Lists a summary of the LSAs in the database, with one line of output per LSA. It is organized by LSA type (first type 1, then type 2, and so on).

show ip route

Lists all IPv4 routes.

show ip route ospf

Lists routes in the routing table learned by OSPF.

show ip route ip-address mask

Shows a detailed description of the route for the listed subnet/mask.

clear ip ospf process

Resets the OSPF process, resetting all neighbor relationships and also causing the process to make a choice of OSPF RID.

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