Advanced Subnetting Details, Sick of Simple!

Unanswered Question
Jul 20th, 2008

Honestly, this gets me so frustrated I can't even think straight. Every book I've purchased, every CBT Video I've bought, every website I've browsed says the same thing!

What's that you ask?

"I'm going to show you a very simple, dumb down, non-explained process just to make it simple for you!"

After reading and doing their method, I'm left sitting here wondering how to subnet. I don't understand, I can't memorize any of these methods and I honestly can't figure out how it works. I just know several methods which have a motto of, "Don't worry about the details, just do this".

As a person I need to understand something to master it. I need to know the grit and grime behind the science. I need to understand exactly what is happening behind the scenes!

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Hi There

Not sure which books/CBT's you have gone through, however the one book I thought had the best explanation of subnetting was the Sybex book "CCNA Study Guide" by Todd Lammle.

It starts off by showing you how you subnet using the long, written down binary maths method, so you understand the mechanics of subnetting. Then moves on to not a "dumbed down" method but a method which will have you subnetting in your head with ease. This is a skill you will need for the exam and indeed throughout your working life in networking.


Best Regards,


scottmac Sun, 07/20/2008 - 10:50

I understand your frustration. IMHO, every new networking person show absolutely learn it "by the bits and masks" including what makes a classfull address a Class A, B, C, D, or E.

Once those concepts are firmly planted, THEN look to ways of shortcutting so you can do it in your head.

There are so many concepts that are based on bit-level (and byte-level)interpretation if students took the time to learn them, it would be so much easier to pick the more advanced concepts later.

"Build the good foundation, then build the house"

The Lammie book mentioned above contains a very good explanation; I too think you'll like it.

Good Luck


howtonetwork Sun, 07/20/2008 - 23:15


have you tried

there are also several videos on YouTube.

It can often take quite some time for subnetting to sink in. I prefer to learn the easy way and then go back to the mechanics behind it for an understanding.

It took me 6 weeks to understand subnetting but now I am teaching it so if I can learn it anybody can.



brianjpisa Fri, 07/25/2008 - 07:56

I learned subnetting from the cisco press CCNA exam cert guide by Wendell Odom....not the newest edition, but the from a few years ago. I had to read the chapter a couple times before I understood, but after doing it for a while everything gets repeatitive and you start seeing patterns. Now I'm a human subnet calculator. Is that one of the books you learned from? Also there is a chapter in the cisco press book, Routing TCP/IP Volume I, by Jeff Doyle that breaks down IPv4 networking and subnetworking.

ChaosInMind Fri, 07/25/2008 - 09:33

I went through all of the following:

* ICND1 Official Exam Cert Guide (Wendell Odom) and all included videos

* CBT Nuggets ICND1

* Sybex book "CCNA Study Guide" by Todd Lammle

* Exam Cram ICND1

* Various Subnetting Videos from Online

* Various documents, wiki's, forums concerning the subject

I went through the information more than just once, trust me. I went through the CBT nuggets subnetting videos approximately six times and each book on subnetting twice, including large articles and documentation on the subject. I think somewhere I went through some RFC's.

As an update though, I passed my CCENT with a 922 on July 21st. I can vouch that if you do not know subnetting YOU WILL FAIL. I took the test once already and bombed because I couldn't answer half the questions/scenarios.

What really pulled it through for me is the CBT Nuggets subnetting videos and the "CCNA Study Guide" by Todd Lammle. Both CBT and Sybex use the exact same method, which was the most detailed and straight forward.

It took a while, and I still don't "understand" whats going on, but I can at least do it very quickly....Which is probably the whole point anyway, right?

So a bit of advice. If anyone "doesn't get" subnetting, just shove it and focus on what they are telling you. My recommendations would be CBT Nuggets ICND1 and Sybex CCNA Study Guide by Todd Lammle.

michael.leblanc Fri, 07/25/2008 - 13:10

Understanding subnetting and masks is too important to ignore. I think you should pursue this until your concern is resolved.

Can you articulate what it is that you don't understand?

Perhaps you should post an example, and work through the "thought process" rather than the scripted methodology.

I'm not talking about a race to see which respondent can give you the whole answer, or the most impressive method.

The goal would be to determine where your misunderstanding lies. At each step through the process, you describe what you believe you understand, and allow it to be commented on, before proceeding to the next step.

juniortech Fri, 07/25/2008 - 16:31

I think this is a real good idea. I too am having a difficult time with subnetting. I would like to see this post continue and perhaps I could have my questions answered as well. I hope ChaosInMind responds.

By the way, thanks for the links to the above subnetting sites.


michael.leblanc Sat, 07/26/2008 - 11:02


If he hasn't expressed interest in pursuing it within a few days, perhaps you can participate in that role.

michael.leblanc Wed, 07/30/2008 - 14:57


Doesn't look like he'll return.

Are there any questions you'd like to pursue?

ChaosInMind Wed, 07/30/2008 - 18:59

Well, I have been monitoring this thread. I'll repeat myself again from my previous post... I passed my CCENT, and nobody will pass it without fluently understating subnetting.

What did I not understand about subenetting? The "Method behind the madness".

It VERY hard to explain, but I'm NOT very good at math.

I reviewed the subnetting tables, I worked the math, I multiplied, I divided, I added, I subtracted, I made my own tables, I analyzed!!!

I looked over the info so much, I finally got it!

Do I really know subnetting? NO! But I can do it! Thats all that matters :-)

I passed with a 922 VS. MY 750


I was just offered a job at $40/HR

If learning math doesnt mean $40/hr to you, YOUR CRAZY!!!!!!




I hate math!

I was never good at it!

Honestly, just keep at it... Nothing will stop you!

brianjpisa Thu, 07/31/2008 - 06:09

I don't know how really not knowing subnetting, but being able to do it works. The way that sounds, it will not help to much in the real world. Answering a multiple choice question on a test is completely different than having to plan or figure out ip addressing for a network. Also, if being unable to "completely" understand ipv4 subnetting down to the bit, then ipv6 will be very hard to learn. Either way keep cracking the books and learning and good luck with the new job.

I realize that your question has been answered in a few ways... but I just wanted to give my 2 cents!

If you want to know subnetting and want to know why and what makes up subnetting... understand two concepts:

1. Binary. Whether you suck at math or a math genius... know your binary. And when it comes down to Cisco... know binary up to 8 bits.

2. Ethernet packet structure. Its all based upon binary but if you can understand the packet... I think (IMHO) you will understand why Cisco uses its subnetting methods.

albert1975 Sat, 08/30/2008 - 03:20

Like having a car and drive it. Do you need to know how the machine works and all that?

If you really know how it works behind the scene, you may have choose a wrong career.

dwgray0422 Fri, 09/12/2008 - 07:32


Aug 30, 2008, 4:20am PST

Like having a car and drive it. Do you need to know how the machine works and all that?

If you really know how it works behind the scene, you may have choose a wrong career.

If you chose to be a mechanic you need to know the inner workings of the car. If you chose to be a network technician, you need to understand the inner workings of TCP/IP.



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