Here you go:
Step 1
Grab a sheet of paper and in the top right corner write the number 1. To the left double it and write 2, to the left double it and write 4 and keep going eight times until you reach 128 which is one binary octet.
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
Step 2
Along the left hand of the sheet to the left of the above row write a column of numbers. Start with 128 and then under that add 64 to it to get 192. Add 32 to it to get 224 then add 16 to it to get 240. Keep going until you have added all the numbers from the top row.
| 128 |
| 192 |
| 224 |
| 240 |
| 248 |
| 252 |
| 254 |
| 255 |
These are all the possible subnet values you could have in a subnet mask.
Step 3
Underneath the above row write out a powers of two column. We use this column for network design questions. These are explained in detail on the subnetting secrets videos.
| 2(-2) |
| 4 |
| 8 |
| 16 |
| 32 |
| 64 |
| 128 |
| 256 |
| etc .. |
That is how you write out the Subnetting Secrets Cheat Sheet. Here it is in full:
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | ||
| 128 | |||||||||
| 192 | |||||||||
| 224 | |||||||||
| 240 | |||||||||
| 248 | |||||||||
| 252 | |||||||||
| 254 | |||||||||
| 255 | |||||||||
| 2 (-2) | |||||||||
| 4 | |||||||||
| 8 | |||||||||
| 16 | |||||||||
| 32 | |||||||||
| 64 | |||||||||
| 128 | |||||||||
| etc ... |
Please write this chart out on a sheet of paper over and over until you can do it by heart. To see how to use the chart please visit the easy way to subnet page for an example. There are over 40 examples using Class A, B and C addresses in Subnetting Secrets along with some network design examples.
