Howard, thanks for your input. Comments inline... Hal
> -----Original Message----- > From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, May 14, 2002 7:22 AM > To: [EMAIL PROTECTED] > Subject: RE: Is IGRP actually supported by other vendors? [7:43994] > > > At 4:25 PM -0400 5/13/02, Logan, Harold wrote: > >You're right about IGRP still being listed on the CCNA > objectives. While > >I've sometimes found it frustrating to teach an outdated > protocol, IGRP is > >useful as a teaching tool. With IGRP you can easily > demonstrate the concept > >of composite metrics, poison reverse, holddown timers, split > horizon, and > >unequal-cost load balancing, but you don't have multicast > updates, neighbor > >relationships, incremental updates, and VLSM's adding to the > confusion. > > You make some interesting instructional points that I want to think > about. Let me make some observations. > > No modern routing protocol uses composite metrics, in the sense that > a numerical value is computed from several factors. I don't know if > you'd consider route preference (e.g., OSPF intraarea over interarea > over external) to be composite; I don't. >From this statement I'm inferring that you don't consider EIGRP to be a modern protocol? If so, I would concede that it's not as scalable as OSPF or IS-IS. But it's still deployed in networks, and anyone going through cisco's certification program has to learn it. Or am I missing something on EIGRP's calculation of a metric based on bandwidth and delay? At any rate, I haven't had enough caffeine today to wrestle with intraarea, interarea, and external routes as part of a composite metric. I suppose if someone really wanted to they could try to argue that External Type 1 routes qualify as a composite metric, but I think even that's pushing it. > Poison reverse, split horizon and holddown are explained decently in > the very readable RIP RFC. Agreed. Whenever possible I like to demonstrate protocols in action, rather than tell a student to take my word for it, or even take an RFC's word for it. Besides, I almost have to threaten physical violence before I can get a student to read an RFC. (Considering that I work for a state-funded community college, physical threats are usually frowned upon) RIP does work nicely along those lines; if a student does some debugging and sees an advertisement go out with a hop count of 16, usually a connection gets made to the idea of advertising a network as unreachable, and viola. Poison Reverse is now associated with a network the student has set up, and seen in action, rather than a paragraph from a textbook or an RFC. The benefit of demonstrating the same concepts again using IGRP is simple reinforcement. > Unequal cost load balancing is increasingly deprecated; there are > better ways to do traffic engineering. That's why I don't spend a lot of time covering it. I do however have an obligation to at least pay lip service to it, enough to ensure that students associate the variance command with UCLB. When Cisco takes it off the cert exams, I'll stop teaching it. > > > >If EIGRP replaces IGRP on the CCNA, then hopefully the > certification team > >will draw a clear line indicating which features of eigrp > will be tested and > >which ones won't. The way things are right now, IGRP makes > for a smooth > >transition from the CCNA to the CCNP Routing exam. Someone > who understands > >IGRP doesn't need to reinvent the wheel to learn EIGRP, > > I'd argue that other than some similarities in commands and metrics, > IGRP and EIGRP are completely different protocols. This is conjecture on my part, as I won't teach my first CCNP class until January... but it seems to me that when put in a class where they have to learn the basics of EIGRP, OSPF, and BGP, students are going to focus first and foremost on the configuration commands. Considering that the only difference between the basic configuration process for igrp and for ip eigrp is the addition of the mask option after the network command (along with the addition of a vowel) I believe that will free up some CPU cycles so that students can focus on DUAL, multiple topology tables, summary addresses, feasible successors, and other new concepts. > There is a trivial case of neighbor relationships in RIP, as a router > with a RIP-enabled interface will suppress outgoing updates until it > hears a RIP query from a router on the medium. That is a form of > neighbor discovery. > > It is different from using a hello subprotocol to know if a neighbor > is still alive. See, I call that a useful comparison. When I field questions, I'd say at least half of them boil down to "how does this compare to what I already know?" > Personally, when I'm teaching beginning IP, I start with binary, and > then VLSM/CIDR becomes a natural idea. I then introduce dotted > decimal, and only as an afterthought mention classes. Works well > whenever I've tried it. I very rarely have the luxury of teaching beginning IP. Usually by the time I get ahold of a networking class they've already been taught how to subnet using the 256 subtraction shortcut, and they've only been taught how to subnet a class C address. So right off the bat, I get people who've been taught how not to use binary, and who have a mental block about subnetting anything other than a class C. The first thing I do when I discuss IP addressing with a class is (try to) tell them with a straight face that I'm too dumb to do the 256 subtraction, and from there we work on unlearning "IP subnetting for dummies." One of the downsides of teaching the networking academy classes for an entire semester rather than doing 2 and 3 week classes is that many of the students expect things to be spoon-fed to them, and don't retain information as well as they might in a seminar format. My experience has been that most beginning networkers need at least 2 solid exposures to binary numbering and IP subnetting before it starts to sink in. > >and once one has > >supernetting and neighbor relationships in his or her belt, > they can deal > >with OSPF area types and LSA's and the like. > > > >Hal Logan CCAI, CCDP, CCNP:Voice > >Network Specialist / Adjunct Faculty > >Computing & Engineering Technology > >Manatee Community College > > -- > "What Problem are you trying to solve?" > ***send Cisco questions to the list, so all can benefit -- not > directly to me*** > ************************************************************** > ****************** > Howard C. Berkowitz [EMAIL PROTECTED] > Chief Technology Officer, GettLab/Gett Communications http://www.gettlabs.com Technical Director, CertificationZone.com http://www.certificationzone.com "retired" Certified Cisco Systems Instructor (CID) #93005 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44245&t=43994 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
