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CCNP Routing Studies: Basic Open Shortest Path First

Chapter Description

Understanding basic Open Shortest Path First (OSPF) routing principles not only applies to the CCNP certification but to all Cisco-based certifications. A concrete understanding of how OSPF routing works is fundamental for any small or large network. This chapter focuses on a number of objectives falling under the CCNP routing principles.


You have now completed some basic and challenging OSPF scenarios and discovered how powerful OSPF is when enabled on Cisco IOS routers.

OSPF can be configured in single or multiple areas. You saw that all OSPF areas must be connected to the backbone for proper and correct operation. Standard techniques using Cisco IOS show commands were demonstrated to ensure that you have all the required knowledge to monitor and maintain small or large OSPF networks.

Table 3-7 summarizes the commands used in this chapter.

Table 3-7 Summary of IOS Commands used in this Chapter



show ip route

Displays IP routing tables.

router ospf process id

Enables OSPF routing. The process ID is local to the router. You can have more than one OSPF running.

network mask

Enables network advertisements out of a particular interface and also the routing of the same interface through OSPF.

show ip ospf

Displays the OSPF process and details, such as OSPF process ID and router ID.

show ip ospf database

Displays router's topological database.

show ip ospf neighbor

Displays OSPF neighbors.

show ip ospf neighbor detail

Displays OSPF neighbors in detail, providing such parameters as neighbor address, hello interval, and dead interval.

show ip ospf interface

Displays information on how OSPF has been configured for a given interface.

ip ospf cost

Interface command that changes the cost of an OSPF interface.

ip ospf priority

Interface command that changes the DR/BDR election process.

ip ospf network

Interface command that changes the network type.

interface loopback number

Creates a loopback interface.

interface Ethernet mod/num

In configuration mode, enables you modify an interface number, for example interface E0/0.

interface serial mod/num

In configuration mode, enables you to modify serial interface parameters by module and interface number. For example, interface S0/0.

no ip domain-lookup

Disables automatic DNS lookup.

ip subnet-zero

Enables you to use subnet zero on a Cisco router.

show ip protocol

Displays all routing protocols in use on a Cisco router.

debug ip ospf adj

Troubleshooting command that displays messages, such as the state of the adjacency, received and sent by a Cisco router from or to neighboring OSPF routers.

hostname name

Configures a name on a router.

[no] shutdown

Enables or disables an interface. All hardware interfaces are shut down by default.