classful networking refers to a method of dividing IP addresses into predefined classes based on their first few bits. It was used in the early days of the internet to allocate IP addresses and manage network routing.
In classful networking, IP addresses are classified into five classes: A, B, C, D, and E. Each class has a specific range of IP addresses reserved for different purposes.
· Class A addresses start with a binary 0 as the first bit and have a range of 1.0.0.0 to 127.0.0.0. These addresses were initially intended for large networks.
· Class B addresses start with binary 10 as the first two bits and have a range of 128.0.0.0 to 191.255.0.0. They were designed for medium-sized networks.
· Class C addresses start with binary 110 as the first three bits and have a range of 192.0.0.0 to 223.255.255.0. They were meant for smaller networks.
· Class D addresses start with binary 1110 as the first four bits and are used for multicast addresses. They are not typically assigned to individual devices or networks.
· Class E addresses start with binary 1111 as the first four bits and are reserved for experimental purposes.
Class A
A Class A network must use 0 as the first value of the IP address and have a network mask of 255.0.0.0 . This means that the first octet of the IP address can only be between 1 and 127 (explained below) and that this is going to be the “network address”
00000001 – 01111111
1 – 127
In a class A address the first 8 bits are the network address
00000101.00011111.01010110.00001101
5. 31. 86. 13
This means our network mask for a class A network would be
255.0.0.0
Class B
A Class B network must use 10 as the first 2 bits of an IP address and have a network mask of 255.255.0.0. This means our network addresses will be between 128.0 and 191.255 (explained below)
10000000.00000000 – 10111111.11111111
128.0 – 191.255
In Class B the first 16 bits are the network address
10000101.00011111.01010110.00001101
133. 31. 86. 13
This means our network mask for a class B network would be
255.255.0.0
Class C
A class C network must use 110 as the first 3 bits of an IP address and have a network mask of 255.255.255.0. This means our network addresses will be between 192.0.0 and 223.255.255 (explained below)
11000001.00000000.00000000 – 01111111.11111111.1111111
192.0.0.0 – 223.255.255
In Class C the first 24 bits are the network address
11000000.10101000.00001010.00001101
192. 168. 10. 13
This means our network mask for a class C network would be
255.255.255.0
Classful networking was based on fixed boundaries between classes, which resulted in inefficient use of IP address space. As the internet grew, classless inter-domain routing (CIDR) was introduced to allow for more flexible allocation of IP addresses and more efficient address usage.
Today, classful networking is less commonly used, and CIDR is the prevailing method for IP address allocation and routing, allowing for variable-length subnet masking and better address management.
