Subnetting Logic

Hello All.
We are know very well subnet means a huge network divided into many sub networks.
so we take small example therefore we easily understand.
Example: company ABC have it's own network id: 220.220.21.0/24. Administrator want to divided into network 8 sub networks.

Answer: There are THREE Easy Step 1 2 3.
Step 1: Here total 8 networks means power(2)n where n is number of bits borrowed from host portions.so total 3 bit cause power(2)3 = 8.Basis on that we find subnet mask for networks is 255.255.255.224. How na? (easy 24 bit + 3 bit borrow so total /27).

Step 2: Calculate Block Size is also easy: last octant is minus from 256.
Block Size = 256 - last octant. (256-224 = 32)

Step 3: So finally we find block size is 32.
we create sub networks easily 0, 32, 64, 96, 128, 160, 192, 224, 256 ohh... wait...
256 it's over. we get first 8 network ids.
minus one from next network id we get broadcast address of current networks like 31, 63, 96, 127, 159, 191, 223, 255.
Between these range are usable IP address in networks.

Thank You,
Regards,
Jignesh