This is good for Cisco exams, and work, if you ever need to figure out subnets on paper.
To figure out the valid addresses in a subnet:
Take the octet that is not 0 or 255, for example starting with 255.255.224.0, take 224, and subtract that value from 256 (256 – 224 = 32). Now make a chart starting at 0, and adding the value from that last step with each line, up to 256 (the note board I got for the CCNA had gridlines, which made it even easier)
| 0 32 64 96 128 160 192 224 256 |
Now, leaving room in between, write on each line the value of the line below, minus 1
| 0 31 32 63 64 95 96 127 128 159 160 191 192 223 224 255 256 |
The values on the left are the valid subnet addresses, and the right is the broadcast address.
If you want, now fill in the valid ranges in between
| Code: |
| 0 1-30 31 32 33-62 63 64 63-94 95 96 97-126 127 128 127-158 159 160 161-190 191 192 192-222 223 224 225-254 255 256 |
There you go, all your addresses, with subnet and broadcast addresses.