Ethan Banks On productivity.

NMC DOiT Vol.2 Scenario 2 Day 2 – Unicast EIGRP + ODR + CDP Tunneling + BGP Conditional Advertisements


I got about 2 and half hours in on the rack tonight. I would have had another 45 minutes or an hour on top of that, but I was tied up with my wife’s new laptop. She was complaining that web images looked lousy, which they did. Since I went to a lot of trouble to buy her the best screen I could get, so to hear it looked nasty was bad news. Long story short, turns out Dell ships the laptop with this particular screen set to dot pitch of 120 instead of the normal 96. So pictures, indeed, looked nasty. So I set it back to 96 dpi, and everything looks crisp, albeit kind of small. :)

Tonight, I got up through BGP in the lab, meaning that all of my IPv4 IGPs + BGP are configured, including redistribution for end-to-end connectivity. Tomorrow, I need to sanity check routes on all routers to make sure I didn’t screw up the redistribution, then proceed into the IPv6 configuration.

Surprises of the day:

  • Unicast EIGRP – I actually had a clue on this one, but wasn’t sure about it until I looked it up. You use “neighbor” statements in the router eigrp paragraph. Note that whereas RIP requires that the interface be passive, EIGRP does not allow the interface to be passive. So how you do unicast RIP updates? Set the interface to passive and configure a neighbor statement. How do you unicast EIGRP updates? The interface must NOT be passive, and configure a neighbor statement.
  • ODR – On-demand routing is indeed on the lab blueprint, although it is NOT on the written blueprint v3. In a nutshell, ODR is intended as a lightweight protocol between stub-routers and a hub. ODR uses CDP to exchange routing information between ODR routers. It’s pretty easy to understand, and there’s not much to configure. So read up, slacker!
  • CDP Tunneling – I mentioned up above that ODR relies on CDP to exchange routes between 2 devices, right? So what happens when you have a Cisco switch sitting in between the 2 routers? That switch knows CDP, too, and will therefore get in the way of CDP messages between the routers. So what you want to do is take the switch out of the CDP loop so that the routers can talk CDP directly, right? Yes – you get the gold star! But how do you do this? Two steps.
    • On the switch interface, “no cdp enable”. Makes sense – you don’t want the switch sending CDP broadcasts out that interface.
    • On the switch interface, “l2protocol-tunnel cdp”. This command instructs the switch to pass CDP through untouched. Nifty, eh? I did not know you could do that until today.
  • BGP conditional advertisements – I learned a lot of stuff about BGP preparing for the written exam. But I did not learn that you can make a BGP router advertise a prefix – or not – based on whether another route is present in the routing table. This is done with the “neighbor xx.xx.xx.xx advertise-map” command.

I can say that just 1.5 labs into the 25 labs I’m planning to do, that I already feel a lot better about this whole thing than I did a few weeks ago. I know this is going to be a lot of work. A lot. But it seems like manageable work. I don’t think my brain is going to explode with impossible task after impossible task. I’m getting a lot quicker already (although I’m far from quick). I’m nowhere close the time I should be doing this in, but I’m making progress just going from lab 1 to lab 2. So that’s encouraging.

1 comment

By Ethan Banks
Ethan Banks On productivity.

You probably know Ethan Banks because he writes & podcasts about IT. For example, he co-authored "Computer Networks Problems & Solutions" with Russ White.

This site is Ethan on productivity--not tech so much.

Find out more on his about page.