Answers

Figure 1: Two Routers with IP Subnets

interface GigabitEthernet0/1
 ip ospf 50 area 0
!
interface GigabitEthernet0/2
 ip ospf 50 area 0
!
router ospf 50
 router-id 1.1.1.1

Example 3: R1 Config

interface GigabitEthernet0/1
 ip ospf 50 area 0
!
interface GigabitEthernet0/2
 ip ospf 50 area 0
!
router ospf 50
 router-id 2.2.2.2

Example 4: R2 Config

Commentary

The legacy method of configuring OSPF uses network statements inside of OSPF router configuration mode. The network command causes the OSPF process to match the interfaces that will be included into the OSPF area specified. The alternative is to use commands inside interface configuration mode to specify that it will be included inside the OSPF area specified. This newer interface method is considered by many to be easier and a more readable configuration method.

For this lab each of the routers will be configured with an OSPF process ID of 50 (this is a locally significant number only). R1 will be configured with a router-id of 1.1.1.1 and R2 will be configured with a router-id of 2.2.2.2 using the router-id command. This command is still located under OSPF router configuration mode even when using interface configuration commands to specify the included OSPF interfaces.

Note the absence of network commands under the router ospf commands.

Individual ip ospf process-id area area-id interface subcommands replace the network command’s purpose. Each of these commands enables the OSPF process listed by number. Because this lab asked you to use process ID 50 on both routers, and to put all interfaces in area 0, the answers show the command ip ospf 50 area 0 throughout the configuration, one per router interface.

Known Issues in this Lab

This section of each Config Lab Answers post hopes to help with those issues by listing any known issues with Packet Tracer related to this lab. In this case, the issues are:

Why Would Cisco Packet Tracer Have Issues?

(Note: The below text is the same in every Config Lab.)

Cisco Packet Tracer (CPT) simulates Cisco routers and switches. However, CPT does not run the same software that runs in real Cisco routers and switches. Instead, developers wrote CPT to predict the output a real router or switch would display given the same topology and configuration – but without performing all the same tasks, an actual device has to do. On a positive note, CPT requires far less CPU and RAM than a lab full of devices so that you can run CPT on your computer as an app. In addition, simulators like CPT help you learn about the Cisco router/switch user interface – the Command Line Interface (CLI) – without having to own real devices.

CPT can have issues compared to real devices because CPT does not run the same software as Cisco devices. CPT does not support all commands or parameters of a command. CPT may supply output from a command that differs in some ways from what an actual device would give. Those differences can be a problem for anyone learning networking technology because you may not have experience with that technology on real gear – so you may not notice the differences. So this section lists differences and issues that we have seen when using CPT to do this lab.

Beyond comparing your answers to this lab’s Answers post, you can test in Cisco Packet Tracer (CPT) or Cisco Modeling Labs (CML). In fact, you can and should explore the lab once configured. For this lab, once you have completed the configuration, try these verification steps. 

1. Each router should have one OSPF neighbor; verify that fact with the show ip ospf neighbor command.
2. Each router should list one OSPF-learned route, which you can verify with the show ip route command. (If you view the links between routers as a WAN link, the OSPF route will be for the remote LAN.)
3. Verify which interfaces are enabled for OSPF with the show ip ospf interface brief command.
4. Verify the OSPF router ID with the show ip ospf database command.