From the blog.

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IEWB Vol.3 PDFs Should Be Fixed + Re-Reading + Equal-Cost OSPF E2s Tiebreaker Is Cost to ASBR

612 Words. Plan about 4 minute(s) to read this.

Brian Dennis contacted me about a post I’d written complaining about the typos in IEWB volume 3. He figured out the source of the differences between the lab tasks and answer key tasks, and told me that the updated PDFs should be available to members really soon. I haven’t checked, but it might be done already. Kudos to IE for sorting out the problem.

I spent several hours over the weekend re-reading all of my posts on the NMC DOiT series. That was a recommendation in a unicast to me from someone who just earned their digits. Re-reading my notes helped reinforce some technical concepts I’ve studied, and also brought to mind some topics I haven’t thought about for a while. I also think I know the direction I would like to head with this site, once I pass the lab exam…if I ever pass the lab exam. :) I want to create a lab series that a candidate can do in sequential order, with escalating difficulty. Lab 1 should be easy – just enough for the candidate to get his feet wet. Lab 2 should build on Lab 1, and so on. Each lab would then be more challenging than the last, at least to a point. I say this because I did all of the NMC DOiT labs from start to finish, 1 to 25. There was no “building” or “ramping up” process. NMC just drops the bomb on you, and off you go. A gentler progression would help the candidate to both create a lab exam strategy and retain key configuration challenges.

Because of the time I spent re-reading my own material, I haven’t completed IEWB volume 3 lab 7 yet. The rack is configured for lab 7, and I printed out the PDFs. I did a first read-through of the lab as well, and ran into an interesting redistribution task. Imagine R4 and R2 sitting at the edge of the EIGRP and OSPF domains, and both routers redistributing EIGRP routes into OSPF as E2’s. The task was to make all the OSPF routers prefer R4 to R2 for the redistributed routes, but not to make any changes on R4 or R2 to accomplish this.

Since you can’t do anything on R4 or R2, the obvious solutions are out: you can’t make R4 redistribute E1’s instead of E2’s; you can’t summarize routes on R2, allowing R4’s more specific routes to be preferred. You have to make a change downstream. Knowing what kind of change to make (and where to make it) means that you know this fact: when presented with 2 identical cost type-5 LSAs, an OSPF router will break the tie by determining the cost to the ASBR that announced the external LSA. Therefore, to make the OSPF domain prefer R4, increase the cost to R2 by putting an “ip ospf cost xx” statement on an appropriate interface in your topology, where “xx” is the cost you’ve assigned. Where did I find that nugget of info? It shows up in chapter 10 of the OECG, 3rd edition (or chapter 11, 2nd edition).

BTW, that entire chapter was a good read. Odom covers redistribution, route summarization, and default routing. Considering some of the thinking and over-thinking I do relating to these specific topics when in a lab, it was a very good time for me to re-read the chapter. There was also a handy chart listing what default-route injection methods are supported by which IGPs. That’s a chart I was going to make myself, only to find it right there in the book.

Default Routing Chart from OECG

Default Routing Chart shown above is
©CCIE Routing & Switching Official Exam Certification Guide 3rd edition
by Wendell Odom, Rus Healy, and Naren Mehta