Solved

Mnemonic for Subnetting

Posted on 2014-02-08
7
463 Views
Last Modified: 2014-02-16
Hi

I’m teaching our trainees how to find out Subnets by mental arithmetic as they need it for School.
This is the way I learned how to.

First we where told to learn and write this chart before the Exams:

chart1
This chart is been calculated so :

chart2
I just learned for MS Exams Subnet Mask /20 - /32. But the trainees must learn /8 - /32. I think this chart can be easily continued till /8. I also told them to lean the power of 2 (till 12). Is this the easiest way? Alternatively, do you have any other better mnemonic’s?

Many thanks in advance
0
Comment
Question by:*** Hopeleonie ***
7 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 39844514
2^(32-n)
0
 
LVL 19

Author Comment

by:*** Hopeleonie ***
ID: 39844530
Hi ozo

Can you please explain 2^(32-n)  in an example?
I was never good in maths :-)

Many thanks
0
 
LVL 44

Accepted Solution

by:
Darr247 earned 167 total points
ID: 39844583
If you work the first chart backwards, you might notice the mask subtracted from 256 tells you how many addresses are in a subnet (then you would subtract 1 for the network ID and 1 for the broadcast IP).
So, for a /29 the mask is
255.255.255.248
256-248=8 -1 (for network ID), -1 (for broadcast) = 6 usable IPs.

Not a mnemonic, but you may also find this to be a useful visualization:
00000000.00000000.00000000.00000000 = /0  = 0.0.0.0
10000000.00000000.00000000.00000000 = /1  = 128.0.0.0
11000000.00000000.00000000.00000000 = /2  = 192.0.0.0
11100000.00000000.00000000.00000000 = /3  = 224.0.0.0
11110000.00000000.00000000.00000000 = /4  = 240.0.0.0
11111000.00000000.00000000.00000000 = /5  = 248.0.0.0
11111100.00000000.00000000.00000000 = /6  = 252.0.0.0
11111110.00000000.00000000.00000000 = /7  = 254.0.0.0
11111111.00000000.00000000.00000000 = /8  = 255.0.0.0

11111111.10000000.00000000.00000000 = /9  = 255.128.0.0
11111111.11000000.00000000.00000000 = /10 = 255.192.0.0
11111111.11100000.00000000.00000000 = /11 = 255.224.0.0
11111111.11110000.00000000.00000000 = /12 = 255.240.0.0
11111111.11111000.00000000.00000000 = /13 = 255.248.0.0
11111111.11111100.00000000.00000000 = /14 = 255.252.0.0
11111111.11111110.00000000.00000000 = /15 = 255.254.0.0
11111111.11111111.00000000.00000000 = /16 = 255.255.0.0

11111111.11111111.10000000.00000000 = /17 = 255.255.128.0
11111111.11111111.11000000.00000000 = /18 = 255.255.192.0
11111111.11111111.11100000.00000000 = /19 = 255.255.224.0
11111111.11111111.11110000.00000000 = /20 = 255.255.240.0
11111111.11111111.11111000.00000000 = /21 = 255.255.248.0
11111111.11111111.11111100.00000000 = /22 = 255.255.252.0
11111111.11111111.11111110.00000000 = /23 = 255.255.254.0
11111111.11111111.11111111.00000000 = /24 = 255.255.255.0

11111111.11111111.11111111.10000000 = /25 = 255.255.255.128
11111111.11111111.11111111.11000000 = /26 = 255.255.255.192
11111111.11111111.11111111.11100000 = /27 = 255.255.255.224
11111111.11111111.11111111.11110000 = /28 = 255.255.255.240
11111111.11111111.11111111.11111000 = /29 = 255.255.255.248
11111111.11111111.11111111.11111100 = /30 = 255.255.255.252
11111111.11111111.11111111.11111110 = /31 = 255.255.255.254
11111111.11111111.11111111.11111111 = /32 = 255.255.255.255

Open in new window


With IPv6 becoming more prevalent, I see less and less usefulness for subnet masks in the future. It's like teaching kids how to do long square roots manually instead of using the SqRt key on their calculators. Not quite as useful as learning long division. You can't memorize EVERYthing, so just remember where to look up some things.
0
Windows Server 2016: All you need to know

Learn about Hyper-V features that increase functionality and usability of Microsoft Windows Server 2016. Also, throughout this eBook, you’ll find some basic PowerShell examples that will help you leverage the scripts in your environments!

 
LVL 84

Assisted Solution

by:ozo
ozo earned 167 total points
ID: 39844705
2^0 = 1
2^1 = 2
2^2 = 2*2 = 4
2^3 = 2*2*2 = 8
2^4 = 2*2*2*2 = 16
2^5 = 2*2*2*2*2 = 32
...
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 166 total points
ID: 39846163
With IPv6 becoming more prevalent, I see less and less usefulness for subnet masks in the future.
Next time you take a Microsoft, Cisco, HP, Juniper exam, tell them you're not going to answer any IPv4 questions.  Let us know how that works out for you.  :-)
0
 
LVL 19

Author Comment

by:*** Hopeleonie ***
ID: 39846487
Next time you take a Microsoft, Cisco, HP, Juniper exam, tell them you're not going to answer any IPv4 questions.  Let us know how that works out for you.  :-)

LOL :-)
0
 
LVL 19

Author Closing Comment

by:*** Hopeleonie ***
ID: 39863931
Thanks to all again!
0

Featured Post

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

SSL is a very common protocol used these days when browsing the web.  The purpose is to provide security to communication, but how does it do it?  There are several pieces at work that have to be setup before SSL will even work and it requires both …
We recently endured a series of broadcast storms that caused our ISP to shut us down for brief periods of time. After going through a multitude of tests, we determined that the issue was related to Intel NIC drivers on some new HP desktop computers …
This is a video describing the growing solar energy use in Utah. This is a topic that greatly interests me and so I decided to produce a video about it.
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…

829 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question