Basic understading of subnetting is required.
Magic Numbers
| 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 |
|---|---|---|---|---|---|---|---|
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
Increment values.
Subnet Masks
| 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 |
|---|---|---|---|---|---|---|---|
| /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 |
255.255.255.128 == /25
These values are for the last octet. Subtract 8 each time you move one octet to the left.
So the values for the 3rd octet would be:
| /17 | /18 | /19 | /20 | /21 | /22 | /23 | /24 |
|---|
255.255.128.0 == /17
Multiples of 32
| 32 | 64 | 96 | 128 | 160 | 192 | 224 | 256 |
|---|
Useful for faster increments.
Useful Links
subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online