Lab 4-1: Implementing OSPF in a Multi-area Environment

Physical Topology Diagram

  • Visual Topology
  • Command Line
  • Task 1: Configuring a multi-area OSPF network.

Visual Topology

Command List

Command Description
network address wildcard mask area id Specifies which interfaces are OSPF capable and links them to an OSPF area
router ospf process id Enters the OSPF router configuration mode
show ip ospf interfaces brief Displays OSPF interface information
show ip ospf neighbor Displays the contents of the adjacency table
show ip protocols Display information about active running protocols.
show ip route Displays the contents of the IPv4 routing table. (best paths)
show ip route ospf Filters the output display to only show OSPF entries in the routing table.

Task 1: Configuring a Multi-area OSPF Network

Step 1: Access the CLI on your router

Step 2: Check that your IPv4 addresses are still in place and create interface loopback0 and assign the IP address from the table below.

R#sh ip int brief
C:\>ipconfig

Rectify any IPv4 address problems

Router Interface IPv4 address Mask
R1 fa0/0 or gi0/0 10.1.1.1 255.255.255.0
R1 fa0/1 or gi 0/1 172.16.1.17 255.255.255.240
R1 loopback 0 1.1.1.1 255.255.255.255
R2 fa0/0 or gi0/0 10.2.2.1 255.255.255.0
R2 fa0/1 or gi0/1 172.16.1.18 255.255.255.240
R2 loopback 0 2.2.2.2 255.255.255.255

Step 3: Enter the OSPF router configuration mode and assign a process id of 1

Do process IDs need to match for routers to form an adjacency?

Step 4: Use the Network command with an explicit wildcard mask to enable the ethernet and the loopback interfaces. Use the table below for their area assignment

Router Interface Area
R1 fa0/0 or gi0/0 1
R1 fa0/1 or gi0/1 0
R1 loopback 0 0
R2 fa0/0 or gi0/0 2
R2 fa0/1 or gi0/1 0
R2 loopback 0 0

Step 5: Enter the sh ip protocol command and write down the router ID

Why did the router select this value.

Is there another way of controlling the router ID and if so, how?

Step 6: Run the sh ip ospf nei command (these are example outputs)

Note that both the router ID and the actual IP address of the neighbours interface are displayed using this command. The top picture displays a neighbour with a router ID of 2.2.2.2 and a connecting interface of 172.16.1.18.

Why do we see a DR and BDR in the pictures above but below we see a DR and DRother?

Using the sh ip protcol command we can find out information about the OSPF configuration.
Run this command on your router and analyze the result.

This display clearly identifies the Router ID, which networks (interfaces) are allocated to which areas, and a maximum equal cost load balancing of up to 4 paths.

Why is it an Area Border Router (ABR) ?

Step 7: View the contents of the IPv4 routing table and would you expect to see any OSPF entries?

You should observe OSPF generated O and O IA entries in your routing table.

Explain the difference between the two?

Step 7: Save your running-config.

Lab Answer Keys:

Recommended For You

About the Author: Linux Tips

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.