IPv4 Address and Class

IPv4 addresses are divided into classes. Below is the class range of IP addresses and default subnet masks:-

Class	Range	Default Subnet Mask
A	1.0.0.0 – 127.255.255.255	255.0.0.0
B	128.0.0.0 – 191.255.255.255	255.255.0.0
C	192.0.0.0 – 223.255.255.255	255.255.255.0

Network mask

A network mask enables you to identify the network portion of an IP Address and the potion that represent the node (host). Class A, B, and C networks have default network masks, also known as natural masks, as shown here:

Class A: 255.0.0.0 (11111111.00000000.00000000.00000000) binary

Class B: 255.255.0.0 (11111111.11111111.00000000.00000000) binary

Class C: 255.255.255.0 (11111111.11111111.11111111.00000000) binary

Class A:

255.0.0.0 (24 bits)

In a Class A address, the first octet is the network portion while the remaining three octets are for the network manager to divide into subnets and  node (hosts). Class A addresses are used for networks that have more than 65,536 hosts (actually, up to 16777214 hosts!).

Class B

255.255.0.0 (16 bits)

In a Class B address, the first two octets is the network portion while the remaining two octets are for the network manager to divide into subnets and nodes (hosts). Class B addresses are used for networks that have between 256 and 65534 hosts.

Class C

255.255.255.0 (8 bits)

In a Class C address, the first three octets is the network portion while,

 the remaining octet is for local subnets and hosts - perfect for networks with less than 254 hosts.

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