Know About IPv4
An IP address (version 4) is a 32-bit sequence of ones and zeros. For every 8 bits, it will be separated by a dot. One example is 11000000.10101000.00000001.00001000. However IP addresses are seldom written in binary as it is very hard for us to remember. So instead of using binary, IP addresses are normally written in decimal. So based on the example, the IP address in decimal is 192.168.1.8.
IP address is a type of OSI Layer 3 address. It is also known as logical address. The range of the IP address in decimal is from 0.0.0.0 to 255.255.255.255. So how many unique IPv4 addresses are there?
Total unique IPv4 addresses: 256 x 256 x 256 x 256 = 4,294,967,296 which is about 4.3 billions. The estimated world's population is 6.8 billions in 2009. If all the people in the world need an IP address, there won't be enough unique address for everyone.
Different classes of IPv4 addresses
There are five classes of IPv4 addresses. The above table shows the 3 commonly used classes of IPv4 addresses, namely class A, class B and class C. The range of IP addresses and other default values for each classes are also shown in the table.
As mentioned in section 5.3, ip address consists of two parts, the network number(ID) and host number(ID). For class A, the first decimal number(or first 8 bits) represents the network ID. For class B, the first and second decimal number(or first 16 bits) represents the network ID. For class C, the first, second and third decimal number(or first 24 bits) represents the network ID. For each class, the remaining number or bits that are not used for network ID will be used as host ID.
IP addresses with the same network ID are belonged to the same network.
Class A examples:
10.1.1.1 and 10.2.2.2 are in the same network
10.1.1.1 and 11.2.2.2 are in the different network
Class B examples:
129.1.1.1 and 129.1.3.3 are in the same network
129.1.1.1 and 129.3.1.1 are in the different network
Class C examples:
192.168.1.1 and 192.168.1.3 are in the same network
192.168.1.1 and 192.168.2.1 are in the different network
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