Answers: Multi-area OSPF 2

By certskills May 5, 2016 09:10

Think back to when you did this lab before looking here for the answer. Did you have to learn about the IPv4 addressing plan to configure the lab? You actually do not have to think about the router interface addresses, as long as you trust that the documentation in the lab figure is correct. That’s just one interesting fact about the OSPF interface configuration option shown in this lab. As always, do the lab first, and then check your answer here.


Figure 1: Multi-area OSPF Topology


Example 1: Core1 Config


Example 2: Core2 Config


Example 3: Branch1 Config


Example 4: Branch2 Config



For this lab you are tasked with configuring the four different routers with OSPF and placing each of the interfaces into their respective areas by using ip ospf interface subcommands. This style of OSPF configuration can be simple to configure, especially if you have good documentation about router interfaces and areas. This lab supplies a figure with the routers, interface numbers, and areas. For about half of the requirements of this lab, all you have to do is issue a command like ip ospf 50 area 0 or similar under each interface.

Work through examples 1 through 4, focusing on only the ip ospf commands under each interface. Compare those commands to Figure 1. You should see the ip ospf 50 area 0 command on both Core1 and Core 2, under the interfaces that connect Core1 and Core2. This command references each router’s local process ID (50), and the area number into which to put that link. Continuing through the various examples:

  • Router Branch1 uses the same ip ospf 50 area 10 command on both interfaces, enabling OSPF process 50 on both, and placing both in area 10.
  • Router Branch2 uses the same ip ospf 50 area 20 command on both interfaces, enabling OSPF process 50 on both, and placing both in area 20.
  • Router Core1 uses the ip ospf 50 area 10 command on its G0/2 interface (which connects to router Branch1), placing that link into area 10.
  • Router Core2 uses the ip ospf 50 area 20 command on its G0/2 interface (which connects to router Branch1), placing that link into area 20.

As for the routers’ process IDs, the lab asks that all routers use process ID 50. Note that all show the router ospf 50 command as a result.

Finally, on the topic of OSPF router IDs (RIDs), the requirements asked you to explicitly configure the RID on Core1 and Core2, so those routers list the router-id and router-id commands, respectively. For the two branch routers, just for variety, the lab asked you to let these routers set their RID based on the IP addresses of their loopback0 interfaces. To make that work, you have to first create the loopback interface (interface loopback 0), and then configure the IP address. (Note that if you tried this on your own lab, you need to create the loopback interface first, before bringing up the OSPF process, so that the loopback interface is up when OSPF comes up.)

Multi-area OSPF 2
IPv6 Special Addresses 1
By certskills May 5, 2016 09:10
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  1. Efrain January 18, 21:47

    Muy bien explicado!

    Algo a señalar es que en vez del área 100 es el área 10 y en vez del área 200 es 20.

    Gracias por compartir tus conocimientos!

    Reply to this comment
    • certskills Author January 19, 09:53

      Hi Efrain,
      Glad you like it!
      Thanks for the notice about the 100/200 for areas instead of 10/20. I just changed the post. Thanks again,

      Reply to this comment
  2. Daniel April 23, 09:33

    Hello Wendell,
    the lab asked to use loopback interfaces IP addresses with a mask of /32, but the answer has as mask, instead of

    Reply to this comment
  3. Josh Gold May 5, 02:51

    Can i use interface range gi0/1-2 for configuring OSPF on the branch routers in order be more efficient / faster?

    Reply to this comment
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