A hub forwards all packets to all ports while a switch learns to associate MAC addresses with ports to make more efficient one-to-one connections. This is one of the less arcane facts you'll learn from this study guide. Here's a more arcane one: The available cable ends for Cisco routers are EITA/TIA-232, EIA/TIA-449, V.35(for CSU/DSU), X.21(for X.25) and EIA-530. Pay close attention because you will be tested. An example multi-choice question asks, "What Cisco layer provides segmentation of contention networks?". Your choices are Access, Physical, Network, Distribution, Core, Transport, Data link.
This study guide highlights the differences between internetworking as a theoretical study and its implementation in the real world. This is the activity for which Cisco sells routers, hubs and switches. Reading this guide to is to glimpse the elephant on whose back rests the virtual world. It's fascinating and hermetic. It contains the spells the Net wizards use to abolish distance.
Like all magic, it is both precise and arbitrary. While 10Base2 can support a bus up to 185m long with 30 hosts 10Base5 can run to 500m and 208 users. But not 501m or 209 hosts because then the magic won't work. This is an excellent study guide for those who find hardcore technology capable of handling millions of events in tiny slivers of a second with utter reliability for months on end utterly fascinating.
Read the section on how the spanning tree protocol prevents network loops forming. By the way, did you know IEEE 802.1d STP supported by Cisco is incompatible with inventor DEC's version? You will. --Steve Patient
Some child psychologists will tell you that you should never talk down to your children. Rather than spoonfeeding 'em baby talk, you should speak to your kids using big words and long complex sentences--which is tougher on the kid at first, but ultimately makes them a lot smarter than they'd ever be from just hearing "goo goo ga ga".
In much the same way, Sybex's CCNA Study Guide is a book that uncompromisingly presents complex material and expects you to live up to it. While the explanations are dense and often intimidating, once you get through this book, you'll be ready to face--and pass!--the treacherous CCNA exam.
Todd Lammle assumes that the reader has a passing familiarity with basic networking concepts, and he launches straight into an in-depth review of the OSI networking model without even mentioning what hubs, routers, and switches are. He then works his way into explaining TCP/IP and TCP/IP subnetting, a notoriously confusing concept for beginners, and in truth, mid-level techies may be temporarily confused here as well.
Unlike many other CCNA study guides, which touch briefly on subnetting and then provide a list of common subnet masks for rote memorization, Lammle really wants you to understand why certain masks and address ranges work. His objective is for his readers to be able to compute subnets on the fly--a task which many network professionals fake to this day--and as such, he takes you deep into the binary mysteries of TCP/IP. The explanations here are real migraine-inducers, but that's more the fault of TCP/IP's innate complexity than Lammle's explanations. Lammle himself admits that he expects his audience to have to reread the TCP/IP chapter at least once--but if you take the time to bear down, do the math, and really study, you'll never need to read another chapter on TCP/IP subnetting again.
The next sections of the book deal with Cisco routing commands, and it is here that the CCNA Study Guide truly shines. Cisco router commands are infamous for providing the user with floods of information, and the incoming tide of network statistics often sends fledgling CCNA trainees into info-shock. When you have three pages worth of data zipping by on your screen, how do you decide what the important bits are?
Lammle does an extremely good job of walking his students through the various Cisco commands. He explains what each command is meant to do, shows how it's done, and then shows you what you should be looking for after it's done. The chapters here are methodical, thorough, and dense, but they hang together excellently. The only problem is that Lammle assumes you'll be practicing these commands on an actual router--and many CCNA students don't have a practice lab to work with. However, if you purchase the CCNA Virtual Lab, a highly recommended piece of software that simulates Cisco routers in an connected environment, you'll have the next best thing to hands-on router experience. A preview edition of the Virtual Lab is included with the book.
The last section of the book is devoted to WAN protocols, and this part of the book is slightly disappointing. While the details presented in the WAN chapters are solid, they seem slightly out of proportion: while Wide Area Networks, and in particular, ISDN, are a reasonably large part of the CCNA exam, the ISDN section here is all of 20 pages. It's not that there's not enough to pass, but Lammle doesn't provide his usual wealth of details in the final chapter.
Like every good certification book, there are quizzes to test your skill, and you won't be lacking for choices here--seven "open answer" questions, 20 multiple-choice questions, and hands-on workshops grace the end of each chapter. The book ends with a 60-question final exam. The questions are moderately hard, and are a good test of your overall comprehension, but you can probably expect to find harder questions on the actual exam.
Rounding out this book is a voluminous hands-on walk-through of Catalyst 1900 Switch configuration, a comprehensive list of CCNA router commands, and a 70-page glossary. In short, this guide is like a stern teacher: it's not always easy to follow, and it's sometimes frustrating. But by the time you're finished, you'll understand the material better than you could have ever dreamed. --William Steinmetz
