What is the Difference Between Classful and Classless Addressing

The main difference between classful and classless addressing is that classless addressing allows allocating IP addresses more efficiently than classful addressing.  

Every device in a network has an IP address. The address helps to identify each device in the network and allows communicating with other devices in the network. An IP address consists of 32 bits. Every 8 bits is an octet, and they are separated by a dot. The address consists of two sections as network ID and host ID. The network ID represents the network while the host ID represents the host. There are two IP addressing types as classful and classless addressing.

Key Areas Covered

1. What is Classful Addressing
     – Definition, Functionality
2. What is Classless Addressing
     – Definition, Functionality
3. What is the Difference Between Classful and Classless Addressing
     – Comparison of Key Differences

Key Terms

Classful, Classless Addressing, Classless Inter-Domain Routing (CIDR), IP Address

What is Classful Addressing

Classful addressing categorizes the IP addresses into five major classes: class A, B, C, D, and E.

Class A addresses allocate first 8 bits for the network and the remaining bits for the host.

Class B addresses allocate first 16 bits for the network and the remaining bits for the host.

Class C addresses allocate first 24 bits for the network and the remaining bits for the host.

Class D addresses do not have the network ID and host ID. These addresses are used for multicasting.

Class E addresses also do not have network ID and host ID. These addresses are reserved for future and for experiments.

Figure 1: IP Address

By reading the first octet, we can determine the class of an address to which it belongs.

1 – 126 – Class A address

128 – 191 – Class B address

192 – 223 – Class C address

224 – 239 – Class D address

240 – 254 – Class E address

Furthermore, the IP address 0.0.0.0 is used for broadcasting while 127.0.0.1 is used as a loopback address.

What is Classless Addressing

Classless addressing is also called Classless Inter-Domain Routing (CIDR). This addressing type helps to allocate IP addresses more efficiently. When the user requires a particular number of IP addresses, this method assigns a block of IP addresses concerning certain rules. And, this block is called a CIDR block and has the required number of IP addresses.

Classless addressing concerns the following three rules when assigning a block.

Rule 1 – All the IP addresses in the CIDR block must be contiguous.

Rule 2 – The block size should be presentable as a power of 2. Moreover, the number of IP addresses in the block is equivalent to the size.

Rule 3 – First IP address of the block must be dividable by the block size.

For example, assume that the classless address is 192.168.1.35/27

The number of bits for the network portion is 27, and the number of bits for the host is 5. (32-27)

Representing the address in binary is as follows.

11000000. 10101000. 00000001. 00100011

The highlighted bits represent the host bits.

First IP address –  11000000.10101000.00000001.00100000 (assigns 0 to all host bits)

192.168.1.32

Last IP address – 11000000.10101000.00000001.00111111 (assigns 1 to all host bits)

192.168.1.63

The range of IP addresses – 192.168.1.32 to 192.168.1.63

Difference Between Classful and Classless Addressing

Definition

Classful addressing is an IP address allocation method that allocates IP addresses according to five major classes. Classless addressing is an IP address allocation method that is designed to replace classful addressing to minimize the rapid exhaustion of IP addresses. Thus, this is the main difference between classful and classless addressing.

Usefulness

Another difference between classful and classless addressing is their usefulness. Classless addressing is more practical and useful than classful addressing.

Network ID and Host ID

In classful addressing, the network ID and host ID changes depending on the classes. However, in classless addressing, there is no boundary on network ID and host ID. Hence, this is another difference between classful and classless addressing.

Conclusion

Classful and classless addressing are two IP addressing types. The main difference between classful and classless addressing is that classless addressing allows allocating IP addresses more efficiently than classful addressing.  In brief, classless addressing can avoid running out of IP addresses that can occur in classful addressing.

Reference:

1. Singhal, Akshay, “Classless Addressing | CIDR in Networking” Gate Vidyalay, 13 Jan. 2019, Available here.
2. Singhal, Akshay, “IP Address in Networking | Classes of IP Address” Gate Vidyalay, 13 Jan. 2019, Available here.
3. “Classful Network.” Wikipedia, Wikimedia Foundation, 8 Jan. 2019, Available here.
4. “Classless Inter-Domain Routing.” Wikipedia, Wikimedia Foundation, 19 Jan. 2019, Available here.

Image Courtesy:

1. “Ipv4 address” By Indeterminate – Own work (Public Domain) via Commons Wikimedia
2. “Internet map 1024” By The Opte Project – Originally from the English Wikipedia (CC BY 2.5) via Commons Wikimedia