I. IP Address Classes
IP addresses consist of 32-bit binary numbers, which is written in 4 groups of 8 bytes (octets) separated by a dot as the example below:
11000000.00010000.00001010.00000001
Or can be written in the form of 4 groups of decimal numbers (0-255) is 192.16.10.1

W

X

Y

Z

IP address consists of 2 parts of the network id and host id, network ID to determine the network address, while the host ID to determine the host address or computer.
Classes of IP address:

Kelas	Network id	Host id	Range	Default subnetmask
A	W.	X.Y.Z	1 - 126	255.0.0.0
B	W.X.	Y.Z.	128 - 191	255.255.0.0
C	W.X.Y	Z	192 - 223	255.255.255.0
D			224 - 239
E			240 - 247

Class Network Host id id Range Default subnet mask

In order to know the class of equipment an IP address, then each must have an IP address in decimal numbers Subnetmask 255 or binary 11111111 indicates a default Subnetmask concerned that the octet of IP address is for a network id, while the decimal or binary 0 is the host id 00,000,000. Actually there are more classes D and E are rarely used but you need to remember, the class D is used for multicast addresses and class E was prepared utuk experiments.
In addition, there are also some additional rules as follows that you also need to know, namely:

• Number 127 in the first octet is used for loopback, ie to test their own computer in the network.
• If an octet consisting of the number 1 means that all broadcast address (sender of the message)
A. Subnetting

Here I'll show a quick way to determine the subnet, it will be useful if you follow the CCNA exam, for example will be used network ID 132.200.0.0 with a 255.255.192.0 Subnetmask same. This method is easier to understand if the described examples and enggunakan following ways:
• From the first octet and the value of a given subnet, IP address can be known is the class to Bdengan octet-3 covered with numbers 192
Use the formula (256 - number octet of the most backward) = 256 to 192 = 64
• well, the subnet that can be used is a multiple of 64, ie 64 and 128
• So the range of IP that has been in the subnet is
132.200.64.1 until 132,200,127,254
132.200.128.1 until 132,200,191,254
191 is the limit of this subnet by the subnet mask, and not exceed 192 (octet end), so we do not need to memorize the table subnetting.
Another example
Suppose we use a class C network ID 192.168.81.0 with Subnetmask 255,255,255,240 in the same way:
•
Calculate (from 256 to 240) = 16, a group of subnets that can be used is a multiple of the number 16, ie 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, and 224
thanks./febtian