Translating the Theory and Practice of OSPF: a CCNA-ish/CCNP Puzzle

Working from home has some pros and cons, of course. With a combo of ice and snow this week in the Midwest US of A, it's been three days with no school, plenty of stuff to get off the driveway, and I always wonder at what age the kid will quit wanting to go play in the snow some more. And we have an awesome built-in sledding hill in the back yard. Anyway... this has nothing to do with OSPF, but I'm heading to the sledding hill as soon as I post - and make up for it tonight.

After a few weeks on the career topics, it's time to get back to some OSPF. Feel free to ask for some other techie topics. I've got MPLS on the radar, but that's not in CCNA, so feel free to ask for a CCNA topic in particular. Anyway, starting in late November, I've made some posts on OSPF, particularly about LSA types. (Go here to see the list of recent posts, and browse around.)

Anyway, I'm going to start a series of a few more OSPF posts with a bit of a puzzle. It's not exactly like an exam question, but it'll maybe generate some thought. The initial parts will be like a complex CCNA topic, and then morph into a level you'd expected in CCNP. First, let's start with this figure:

The figure shows the pertinent interfaces, IP addresses, and OSPF areas. Note that the interfaces near the top that aren't in areas 1 or 4 are in area 0; it was just too cluttered with the additional area circle. And you can ignore networks 11.0.0.0 and 21.0.0.0 for now.

Next, look at this link. I can't make the output from a router look nice in the blog as text, and there are width restrictions in the blog with figure widths - so just open the link in another window.

With the figure and command output in mind, your job, if you want to work the puzzle, is to:

  1. Build a minimal OSPF config for all 5 routers that would conform to the details in the figure as well as in the output of "show ip route".
  2. You cannot change the reference bandwidth.
  3. The configuration should ignore any external routes.
  4. After completing your configuration, make a list of all alternative configurations that result in the same OSPF metrics as shown in the output of "show ip route".

I'll leave this one out there until early next week, and then start examining what's there.

If you do have questions, comments, etc, please post, but if you don't mind, don't put the answers in your heading, and skip a few lines before listing any of your opinions on the answers. Just don't want to give the answer away to others.

Off to the sledding hill!

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