In yesterday's post, titled "Have you seen my Router ID?", a challenge section was provided. This post will focus on scrutinizing the section itself, from a strategy / analysis point of view.
From a high level overview, we have two devices peering OSPF over a FastEthernet link, with some loopback networks advertised by one side, and received on the other router. If that was all that the section was asking for, then it should be a task that anyone at CCNA level could complete. When looking at the higher levels of certification, to some point you're still configuring some of the same items, but you are expected to know more and more about the underlying technologies, theories, and interactions.
Just like other practice lab sections, we are provided with a list of bullet points. In order to get full credit for the section, we need to make sure that we are meeting ALL of the stated requirements. In the event that you don't know how to complete ALL the items, you are usually better off skipping the section, unless it is needed for core connectivity. When you're in the studying phase, it's also a good idea to play "what if", and ask yourself how you would achieve the task if the section were worded slightly differently.
Make sure that you take the time to read carefully, rather than just diving into a configuration. Make sure that you are carefully taking the time to understand exactly what is being asked.
Taking a look at the individual bullet points:
1. R2 should see networks A, B, and C as OSPF routes in R2's routing table, but they should not appear as IA, E2, or E1.
Here we have a general requirement, but it is coupled with a restriction. With a solution in place, this should be easy to verify.
- What are the different types of OSPF routes that you might see in the routing table?
- Of the various OSPF route types, are there any that are NOT possible, given the information in the section?
- If there are route types that are NOT possible, why are they not possible?
- If the section was worded differently, and for example said they SHOULD appear as a certain type, do you know how you would configure that?
Self assessment: Will your proposed solution meet the requirements of this bullet point?
2. The output of “show ip ospf neighbor” on R2 should show 220.127.116.11 as the Neighbor ID for the adjacency to R1, even if R1 is reloaded. No other Neighbor IDs should show up on R2.
More requirements and restrictions, but still very straightforward regarding how to verify that a solution meets the requirements of this bullet point.
- What is the significance of R2 showing 18.104.22.168 as the Neighbor ID for the adjacency?
- What types of situations would cause a reload to have an effect on the Neighbor ID?
- What would cause R2 to see other Neighbor IDs?
Self assessment: Will your proposed solution meet these requirements?
3. You are not allowed to use the "router-id" command on R1.
This bullet point is an explicit restriction.
- What does the "router-id" command do?
- If this restriction was not here, would your solution be different?
- If the section was worded differently, and you were REQUIRED to use this command, do you know how to use it?
Self assessment: Were you careful to make sure your proposed solution was not using this command?
4. You are not permitted to shut down interfaces on R1, or remove any of the existing configuration on R1.
- How could shutting down an interface affect this scenario?
- How could removing configuration affect this scenario?
5. No additional configuration may be added to R2, all configuration for this challenge is done on R1.
Mostly just excess clarification here, to point out that only R1 needs to be configured.
Knowledge question: Would being able to make configuration changes on R2 affect anything in this scenario?
Note: The questions listed here are just some samples of the types of things that you might be thinking or asking yourself when practicing a technology, or working through a lab scenario.