Subnetting

Applying a subnet mask to an IP address allows you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s.

Default subnet masks:

• Class A - 255.0.0.0 - 1111 1111 . 0000 0000 . 0000 0000 . 0000 0000
• Class B - 255.255.0.0 - 1111 1111 . 1111 1111 . 0000 0000 . 0000 0000
• Class C - 255.255.255.0 - 1111 1111 . 1111 1111 . 1111 1111. 0000 0000

For an IP range = 256 ( 0 - 255 )
0 is a Network Address, while 255 is a Broadcast Address. This number can't be used/set as an IP address. Any IP number that were set as a Network/Broadcast Address can't be used.


eg. A customer/client needs you to set 4 subnet for her/him. What can you do?
255 . 255 . 255 . 0
0000 0000
1100 0000
2^n = 4
2^2 = 4
▒ 4 -> segments
▓ Subnet mask = 128 + 64 = 192
▓ Subnet = 2 (1's) = 2^2 = 4
▓ Hosts = 2 (0's) = 2^6 = 64

Table of Network, Broadcast, & IP range

Network	Hosts		Broadcast Address
	from	to
192.168.1.0	192.168.1.1	192.168.1.62	192.168.1.63
192.168.1.64	192.168.1.65	192.168.1.126	192.168.1.127
192.168.1.128	192.168.1.129	192.168.1.190	192.168.1.191
192.168.1.192	192.168.1.193	192.168.1.254	192.168.1.255

eg. In KISMEC, there were 9 dept. You were ask to create 9 subnet for them. Calculate it?
255 . 255 . 255 . 0
0000 0000
1111 0000
2^n = 16
2^4 = 16
▒ 16 -> segments
▓ Subnet mask = 128 + 64 + 32 + 16 = 240
▓ Subnet = 2 (1's) = 2^4 = 16
▓ Hosts = 2 (0's) = 2^4 = 16

Table of Network, Broadcast, & IP range

Network	Hosts		Broadcast Address
	from	to
192.168.1.0	192.168.1.1	192.168.1.14	192.168.1.15
192.168.1.16	192.168.1.17	192.168.1.30	192.168.1.31
192.168.1.32	192.168.1.33	192.168.1.46	192.168.1.47
192.168.1.48	192.168.1.49	192.168.1.62	192.168.1.63
192.168.1.64	192.168.1.65	192.168.1.78	192.168.1.79
192.168.1.80	192.168.1.81	192.168.1.94	192.168.1.95
192.168.1.96	192.168.1.97	192.168.1.110	192.168.1.111
192.168.1.112	192.168.1.113	192.168.1.126	192.168.1.127
192.168.1.128	192.168.1.129	192.168.1.142	192.168.1.143
192.168.1.144	192.168.1.145	192.168.1.158	192.168.1.159
192.168.1.160	192.168.1.161	192.168.1.174	192.168.1.175
192.168.1.176	192.168.1.177	192.168.1.190	192.168.1.191
192.168.1.192	192.168.1.193	192.168.1.206	192.168.1.207
192.168.1.208	192.168.1.209	192.168.1.222	192.168.1.223
192.168.1.224	192.168.1.225	192.168.1.238	192.168.1.239
192.168.1.240	192.168.1.241	192.168.1.254	192.168.1.255

For more help on calculating subnet mask, click here.
For information on IP Classes, click here