NMC DOiT Vol.2 Scenario 8 Day 2


Not one of my better days at work. Hopped from one early morning issue where we largely failed to recreate a problem we’ve been troubleshooting, then moved to a crisis, where one of our big mainframes was in a death spiral. I escaped work after the mainframe crisis, made it home a bit early, and crashed for a couple of hours with one of the cats. Then I got up and worked on scenario 8 for a two and a half or three hours. I spent most of the time nailing down all of the connectivity issues and lighting up the IGPs. Then I reviewed the redistribution scenario on paper, trying to think through all of the potential problems. I didn’t actually try to write code to support the redistribution, since my brain isn’t in top form right now. But I drew a big picture with lots of arrows, and wrote down things I think may be important. Tomorrow or Thursday, I’ll actually do the redistribution and make sure I meet all the scenario requirements for what routes are supposed to converge on who.

Then I should be able to get BGP done, although I’m still not sure how to do it. I drew out the BGP scenario, but I’m not sure yet if there’s some gee whiz feature of BGP I’m supposed to use to fulfill the requirements or not…it’s kind of a weird layout. I think I have a solution to meet the requirements using what I already know about BGP, but the requirements has funny wording, giving me that vibe that there’s a command or two I’m not aware of that’s probably the desired answer. Thursday/Friday/Saturday, I should be able to get the rest of the scenario done. There’s a bunch of QoS stuff to do, particularly on the Catalyst 3560, which seems to come up more frequently than I would have expected, and a number of miscellaneous tasks.

I think the NMC ratings on “hard” versus “moderate” scenario difficulties are nonsense. I’m finding each scenario comparably difficult, plus I think that they are getting slightly harder as they have progressed. For instance, this scenario featured CHAP authentication over frame relay. My brain said, “Hey, you can’t do CHAP over frame – that’s a PPP technology.” And my brain was right. You have to run PPP over the top of frame-relay…and then run CHAP. So that was a trip down IOS documentation lane to figure that out. Then the scenario wanted me to do frame-relay between 2 routers with no frame switch in the middle, and neither router acting as a frame switch, either. You need a “no keepalive” on the serial interfaces to make that magic happen. Plus the scenario wanted me to make RIP run on a link where the IP addresses on either end of the link were members of a different subnet. And that magic is the “no validate-update-source” command in the “router rip” paragraph. Stuff like that seems trivial perhaps, but when those kinds of things are critical for basic connectivity and IGP task fulfillment, they can be maddening when you don’t know the answer. I guess that’s the point of the practicing, right? To be exposed to all these IOS features that you may never use in real life, but that you need to master to truly be an expert.

Ah, well – I am beat. Heading back to bed, so that I can get up and do it all over again in the morning. I think I have a bunch of change controls to do first thing in the morning. Woo hoo!

By Ethan Banks

Ethan Banks is a podcaster and writer with a BSCS and 20+ years in enterprise IT. He's operated data centers with a special focus on infrastructure — especially networking. He's been a CNE, MCSE, CEH, CCNA, CCNP, CCSP, and CCIE R&S #20655. He's the co-founder of Packet Pushers Interactive, LLC where he creates content for humans in the hot aisle.