Subnetting Study Stages

By CCENTSkills February 20, 2018 13:05

IPv4 subnetting sits at the top of the list of challenges for #CCNA. I’m wrapping up the development of a new subnetting course, and as a result, I’ve been thinking a lot about how people learn about subnetting. How do you move from first learning the basics of subnetting, to mastering subnetting well enough to pass the CCNA Exam? I’ve broken the process into several stages for the course (you’re welcome to attend – next one is March 13-14). I also thought the rest of you might be interested in those subnetting learning stages, so I’ve made a few blog posts about it.

Three Stages of Learning Subnetting for the Exam

Subnetting uses many processes, each with small bits of math, with each process supplying some facts or analysis about IPv4 addressing or subnetting. The figure shows a list of the most common procedures. For instance, the process called “convert masks” might be helpful if a question listed a subnet mask in dotted decimal notation (DDN), but you might need to think about the mask in binary or prefix notation.

If you think about the progression of how someone new to subnetting might learn the “convert masks” process, you can see several steps along the way to becoming fully ready to do well on the exam. Before the exam, you need to:

  1. Learn the Concepts and Process(es):
    • Learn that masks can be written in three different formats
    • Realize that you can benefit from working with a mask in a different format (motivation to change formats)
    • Learn the conversion process(es)
    • Memorize the conversion process(es)
  2. Perfect Your Skills Using the Process(es):
    • Practice the process until you can correctly convert the mask every time
    • Practice without notes (as if you are taking the exam)
  3. Accelerate to Exam Speed:
    • Practice to improve your speed


The subnetting learning stages idea breaks the learning process into the same three steps shown above. For the course, I’ll ask the students a question that quickly identifies whether they are in stage 1, 2 or 3 for any particular topic in subnetting, using the ideas in Table 1. Following the table, I’ll get into a little detail on each stage.

Stage Primary Study Goal Understood and Memorized Ideas and Processes? Do You 
Get 100% Correct? Do You

Go Fast?

1 Learning No
2 Perfecting Yes No
3 Accelerating Yes Yes No
4 Completed Yes Yes Yes

Table 1: Stages and Questions


Stage 1: Learning (While Ignoring Accuracy and Speed)

For any part of the varied subject area of subnetting, ask yourself that first question, in the middle column of the table. If the answer is still “No,” you are still in stage 1. The question:

Have you understood and memorized the ideas and processes?

For instance, with the earlier example of converting subnet mask formats, do you:

  • Understand the three mask formats and the meaning of each?
  • Do you understand how to convert from DDN to prefix notation? Vice versa?
  • Memorization: Could you empty your desk and computer of all your notes, and convert the following masks to the other two formats, without using your notes?
    • /27
    • 255.252.0
    • 11111111 11111111 11100000 00000000

Do not be discouraged by being at stage 1! Everyone begins knowing little or nothing. Then you spend a little time in stage 1 while learning before moving on to stage 2. While in stage 1, you just need to do slightly different activities compared to stages 2 and 3 (more on study activities in the next post).


Stage 2: Perfecting (While Ignoring Speed)

I call stage 2 the “perfecting” stage because you are perfecting your skills. To reach stage 2, you have to answer that first question with a “Yes,” but the second question with a “No”.  That is:

Yes: you have completed your learning. You understand and have memorized the concepts and processes.

No: Could you get all questions correct if given a test right now, with no notes available?

Expounding a bit, if you have completed stage 1, you understand the topic, and you have memorized the process. However, you may not have done enough practice problems yet so that you get every answer correct. Maybe you get 100% of the more natural questions correct but struggle with the more difficult problems. It’s like math class in school – we all do better with some practice.

Summarizing the ideas of the stage 2 question which puts you in stage 2 if you answer “No”:

Do you get 100% of the questions correct, with no notes available, but with all the time you need?


Stage 3: Accelerating

I call this third stage the accelerating stage because your goal is to get faster and faster. When you reach stage 3, you have gotten to the point at which you can get the right answer consistently, with no notes available, but without rushing. Stage 3 asks you to accelerate your speed until you go fast enough for the exam.

Why go fast? The need for speed has everything to do with the exam. In real life, you may not need to perform many of the subnetting processes at the speeds required to do well on the CCNA exam. The exam, of course, includes some time pressure, and one of the best ways to reduce time pressure is to perform subnetting processes with speed.

The question that helps you determine if you are in stage 3 is:

Do You Go Fast?

If you now answer “Yes” to the first two questions, but answer “No” to this question, you have reached stage 3. But of course, this latest question begs an obvious question: how fast is fast enough? In my Cert Guides, I suggest a goal for many subnetting processes, and I’ve listed those in table 2 – but you should set your own goals.

Subnetting Processes Book Speed Goals Your Speed Goal
Classful Networks: Find Key Facts * 10
Converting Subnet Mask Formats * 10
From Address/Mask, Find Subnet ID, Broadcast Address, and Address Range 30
Interpret Design Based on Mask to Predict # Subnets, # Hosts/Subnet 15
Based on Design Criteria, Choose 1 Mask 15
For Network w/ 1 Mask, Find All Subnet IDs 45

*Time to think, ignoring the time to write

Table 2: Subnetting Processes and Speed Goals


What’s Your Stage for Each Process?

To wrap today’s post, think for a moment about where you are in your CCNA journey and CCNA study. At what stage are you for each of the subnetting processes listed in Table 3 below? I’d be curious to know – post a comment here, or tweet @WendellOdom (even use the #IPv4Subnetting hashtag we’ll use for the upcoming course).

Subnetting Processes Described Shortname At What Stage are You Today?
Classful Networks: Find Key Facts * Network Facts
Converting Subnet Mask Formats * Convert Masks
From Address/Mask, Find Subnet ID, Broadcast Address, and Address Range Subnet Facts
Interpret Design Based on Mask to Predict # Subnets, # Hosts/Subnet Interpret Mask
Based on Design Criteria, Choose 1 Mask Choose Mask
For Network w/ 1 Mask, Find All Subnet IDs Find Subnets

Table 3: Subnetting Processes: What’s Your Stage?

Next post, I’ll give you a few suggestions about how to study depending on your stage. Hope to see you in the upcoming live IPv4 Subnetting course on March 13-14! (If you want to learn more about live training on Safari, check out this earlier post.)












Wendell is Teaching Again! Live Courses on Safari.
Subnetting Study Stages and Stage 1 (Learning)
By CCENTSkills February 20, 2018 13:05
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