Home > learning, routing, switching > How much do you REALLY know about technology X?

How much do you REALLY know about technology X?

Think about something you know a fair amount about. It can be anything in the realm of networking. Now imagine yourself explaining it to someone. Not just anyone. Someone who has a decent grasp on it, but maybe not all of the particulars. Can you explain it to them on the fly without stammering and stuttering your way through it?

I am a Twitter addict. I use it primarily for IT related stuff. There are plenty of valuable links and comments that show up on a given day. Amazing things. Things I never thought about. Comments that come from people who’s books I have read. Comments that come from 4 and 5 time CCIE’s. Comments that come from people who’s podcasts I listen to every week driving to and from work. In short, it is almost as if you know them on some weird Internet non-stalker type level.

Today I saw and even somewhat participated in a discussion about EIGRP. That got me thinking. I like EIGRP. I think it’s neat as far as routing protocols go. It doesn’t have the whole “standards” thing going for it like OSPF or IS-IS. It doesn’t run the Internet like BGP. There aren’t very many books written about it. The CLI options are a lot smaller when compared to OSPF and BGP. The list goes on and on. The more I thought about it, the more I realized I don’t have the complete understanding of it that I wish I did.

Replace EIGRP with about 20 or 30 other networking technologies/protocols and I can make the same argument. I may know all the little acronyms or terms that go along with that technology or protocol, but can I break it down and explain it to someone who sort of understands it and just needs the finer points? Isn’t that what separates the really good engineers from the average ones?

Back to EIGRP though. I understand metric calculation. I understand K values. I understand several other things about EIGRP that go beyond the CCNP level and possibly approaching, maybe even exceeding, CCIE level. I am not bragging. I’ve just put in the hours from an “academic” standpoint, which translates to reading a lot of books, design guides, whitepapers, etc about EIGRP. However, I find myself struggling to come up with all of the arguments for why EIGRP is a hybrid routing protocol compared to a distance vector protocol and vice versa. There are people out there who swear it is one or the other. That should be a relatively simple thing to discern. It makes me think I really don’t understand EIGRP as well as I think I do. Granted, you can NEVER know it all about anything in the IT field, but we still have to try. We read questions on forums from people just starting out with something like EIGRP and think: “How could you not know that? Everyone knows that K1 is bandwidth and K3 is delay.” Maybe we pass by a CCNA book at the bookstore and chuckle at how trivial the description is of EIGRP. “What? You don’t even mention stub routers or how to avoid SIA conditions?” Admit it. You do it. If you don’t, then you are truly the example of a good engineer.

What to do about this? Well, I should study more. I should study and lab so much that when a CCIE walks up to me and says: “How does EIGRP do this?”, I can answer them in a fair amount of detail and even break out the whiteboard and draw it out. Or, crank out a config in a few minutes. Imagine if you knew the protocol or technology so well that you could just spew forth tons of factual information about it? Imagine if you could sit down with a blank piece of paper and fill it up on both sides with information about something like DWDM, 802.11n, PPP, or HSRP. What would that be like? Not just know from an academic standpoint, but be able to apply it to real world scenarios. There is tremendous value in that.

Just something to think about. Imagine having to teach cooking to Emeril. Or martial arts to Chuck Norris. Or basketball to Michael Jordan. Would you want to know your stuff? You betcha. Think about the things you deal with in the networking world and apply the same philosophy to it.

When I begin to understand something well enough to teach it to people that understand it as well and not have them laugh me out of the room, I will be at the level I want to be at. Impossible to do with all things network related, but definitely achievable to do with a dozen or so things. Perhaps the hardest part of it is dedicating the time to achieve that level of proficiency.

I’m going to revisit EIGRP over the next couple of weeks and try to increase my level of understanding even more. Then, I will read someone’s blog post or Twitter comment and realize how little I actually know and go back and do it all over again. Frustrating? Sure, but I will take that any day over a job where you can learn it all in a couple of months. Happy learning!

Categories: learning, routing, switching
  1. July 29, 2010 at 1:42 PM

    Well, the reason EIGRP is not a truly DV protocol is the ACTIVE/query/response thing. A DV protocol just redistributes what it knows (think RIP or BGP), it never actively queries others.

    • July 29, 2010 at 5:27 PM


      Thanks for the comment. You’ve just given perhaps the best argument I have heard to date for why EIGRP is not a DV protocol. Of course, after writing a book on EIGRP, I am sure you have a fairly good understanding of it. 🙂 Most of the books, blogs, white papers,etc that I have read regarding EIGRP mention that it is a DV with some LS features. Inevitably the word “hybrid” comes up. However, there are people out there that definitively state that EIGRP is a DV protocol. Take this presentation for example:


      It isn’t until the very end of the presentation that EIGRP is mentioned as having link state properties. The entire time it is compared to RIP. Additionally, I disagree with slide 26 where EIGRP is shown to be complex in implementation and maintenance. On top of that, this is a Cisco Networking Academy presentation! It seems as if there is a rather large attempt to categorize EIGRP as DV with just a little touch of LS. That’s where I get a little frustrated. Maybe it’s a small thing, but it bothers me all the same.

      • July 30, 2010 at 12:50 AM

        Well, to be honest, EIGRP has zero (0.0000) LS features. A router using link-state protocol can use authoritative information from routers beyond its immediate neighbors (the LS topology database) to make routing decisions (the SPF algorithm).

        EIGRP has no information whatsoever beyond what the neighbors advertise in their routing updates; the only thing it can do that makes is different from a traditional DV protocol is that it can actively ask the neighbors for new information instead of passively waiting for the updates.

  2. July 30, 2010 at 11:26 AM

    I appreciate your responses! It seems the deeper I go down the rabbit hole, the more confusing it gets.

    From chapter 6 (Understanding EIGRP) of Troubleshooting IP Routing Protocols I read this:

    “EIGRP is neither a classic distance vector routing protocol nor a link-state protocol—it is a hybrid of these two classes of routing protocol. Like a distance vector protocol, EIGRP gets its update from its neighbors. Like a link-state protocol, it keeps a topology table of the advertised routes and uses the Diffusing Update Algorithm (DUAL) to select a loop-free path.”

    On the other hand, from chapter 4 (Dynamic Routing Protocols) and chapter 7 (EIGRP) of Routing TCP/IP Volume 1, I read the following:

    Chapter 4:”Distance vector routing protocols include the following:

    * Routing Information Protocol (RIP) for IP

    * Xerox Networking System’s XNS RIP

    * Novell’s IPX RIP

    * The Cisco Systems Internet Gateway Routing Protocol (IGRP) and Enhanced Internet Gateway Routing Protocol (EIGRP)

    * DEC’s DNA Phase IV

    * AppleTalk’s Routing Table Maintenance Protocol (RTMP)

    Chapter 7: “First released in IOS 9.21, Enhanced Interior Gateway Routing protocol (EIGRP) is, as the name says, an enhancement of the Cisco Interior Gateway Routing Protocol (IGRP). The name is apt because unlike RIPv2, EIGRP is far more than the same protocol with some added extensions. Like IGRP, EIGRP is a distance vector protocol and uses the same composite metrics as IGRP uses. Beyond that, there are few similarities.”


    “EIGRP is occasionally described as a distance vector protocol that acts like a link-state protocol. To recap the extensive discussion in Chapter 4, “Dynamic Routing Protocols,” a distance vector protocol shares everything it knows, but only with directly connected neighbors. Link-state protocols announce information only about their directly connected links, but they share the information with all routers in their routing domain or area.”

    Both of those sources I cited are “CCIE” references that people use to educate themselves, or to study for the CCIE lab exam.

    Additionally, here is what chapter 2 (Configuring EIGRP) of the Cisco IP Routing (ROUTE) Foundation Learning Guide has to say about EIGRP:

    “EIGRP is a Cisco-proprietary protocol that combines the advantages of link-state and distance vector routing protocols. EIGRP has its roots as a distance vector routing protocol and is predictable in its behavior. Like its predecessor IGRP, EIGRP is easy to configure and is adaptable to a wide variety of network topologies. What makes EIGRP an advanced distance vector protocol is the addition of several link-state features, such as dynamic neighbor discovery.”

    That book is used by CCNP candidates to study for their ROUTE exam. It appears to have the clearest explanation from the Cisco Press books that I have seen yet, and no, I have not read your EIGRP book yet. It’s on my list though.

    From the description that came from the ROUTE book above, it appears to be the closest to what your description of EIGRP is. Maybe in the grand scheme of things it doesn’t really matter if a bunch of people call EIGRP a DV/LS hybrid. Or maybe it does. You have made some good points in regards to why EIGRP is not an LS protocol and why it is not truly a DV protocol. These kinds of things, small as they may seem, actually matter to me. Thanks again for your comments.

    • July 30, 2010 at 11:38 AM

      Amazing how much misinformation there is out there. EIGRP is no more a LS routing protocol than BGP; they don’t have a clue what’s behind their immediate neighbors, they just don’t forget the stuff they don’t currently need.

      Likewise “dynamic neighbor discovery” has nothing to do with LS routing protocols (apart from the fact that RIP does not do it). In the same vein, BGP with anonymous neighbors has some LS functionality 😀

      On a tangential topic: Can I use your research (obviously with proper attribution) for an “EIGRP myths debunked” post?

      • July 30, 2010 at 11:42 AM

        Absolutely! Feel free to use whatever you need. I look forward to reading your post. Thanks.

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