This chapter covers the following exam topics:
3.0 IP Connectivity
3.2 Determine how a router makes a forwarding decision by default
3.2.b Administrative distance
3.2.c Routing protocol metric
3.4 Configure and verify single area OSPFv2
3.4.a Neighbor adjacencies
3.4.b Point-to-point
3.4.c Broadcast (DR/BR selection)
3.4.d Router ID
OSPFv2 requires only a few configuration commands if you rely on default settings. To use OSPF, all you need to do is enable OSPF on each interface you intend to use in the network, and OSPF uses messages to discover neighbors and learn routes through those neighbors. OSPF performs many background tasks, and you can discover details about that work using a large number of OSPF show commands. However, configuring OSPF, using mostly default settings for all the optional features, requires only a few commands. This chapter sets about to help you learn those minimal settings.
The first major section of this chapter focuses on traditional OSPFv2 configuration using the network command, along with the large variety of associated show commands. This section teaches you how to make OSPFv2 operate with default settings and convince yourself that it really is working through use of those show commands.
The second major section shows an alternative configuration option called OSPF interface mode, in contrast with the traditional OSPF configuration shown in the first section of the chapter. This mode uses the ip ospf process-id area area-number configuration command instead of the network command.
Along the way, the first major section includes the detail of how to set the OSPF router ID (RID). While optional, configuring a predictable and stable OSPF RID allows easier operation and troubleshooting of OSPF and may be the most important of the optional OSPF settings.
“Do I Know This Already?” Quiz
Take the quiz (either here or use the PTP software) if you want to use the score to help you decide how much time to spend on this chapter. The letter answers are listed at the bottom of the page following the quiz. Appendix C, found both at the end of the book as well as on the companion website, includes both the answers and explanations. You can also find both answers and explanations in the PTP testing software.
Table 22-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping
Foundation Topics Section |
Questions |
|---|---|
Implementing OSPFv2 Using network Commands |
1–4 |
Implementing OSPFv2 Using Interface Subcommands |
5, 6 |
1. Which of the following network commands, following the command router ospf 1, enables OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?
network 10.0.0.0 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
network 10.0.0.0 0.0.0.255 area 0
network 10.0.0.0 0.0.255.255 area 0
2. Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?
network 10.1.0.0 0.0.255.255 area 0
network 10.0.0.0 0.255.255.0 area 0
network 10.1.1.0 0.x.1x.0 area 0
network 10.1.1.0 255.0.0.0 area 0
3. Which of the following commands list the OSPF neighbors off interface serial 0/0? (Choose two answers.)
show ip ospf neighbor
show ip ospf interface brief
show ip neighbor
show ip interface
show ip ospf neighbor serial 0/0
4. When reloading and choosing a new OSPF router ID (RID), a router had working interfaces loopback 1 with IP address 10.8.8.8, loopback 2 with address 10.7.7.7, and GigabitEthernet0/0/0 with 10.9.9.9. The router did not have a router-id command in the OSPF process configuration. What RID did the router choose?
10.7.7.7
10.8.8.8
10.9.9.9
The router would fail to choose an RID.
5. An engineer migrates from a more traditional OSPFv2 configuration that uses network commands in OSPF configuration mode to instead use OSPFv2 interface configuration. Which of the following commands configures the area number assigned to an interface in this new configuration?
The area command in interface configuration mode
The ip ospf command in interface configuration mode
The router ospf command in interface configuration mode
The network command in interface configuration mode
6. An enterprise avoids using the OSPF network command, instead preferring to enable OSPF per-interface with the ip ospf process-id area area-id interface subcommand. Which show command identifies whether an interface has been configured with the ip ospf process-id area area-id interface subcommand? (Choose two answers.)
The show ip ospf interface command
The show ip ospf interface brief command
The show ip ospf neighbor command
The show ip protocols command