Classful Addressing Vs. Classless Addressing

How To Stop DNS Hijacking?

Classful Addressing Vs. Classless Addressing

The Internet is an integral part of our everyday life. It is important to know whether the Internet Protocol (IP) of the internet we use follows Classful or Classless addressing systems. So, what is the difference between Classful Addressing and Classless Addressing?

The main difference between classful and classless addressing is that classful addressing is divided into three parts: a network, subnet, and host, and classless addressing is divided into two parts: subnet and host. Thus, classless addressing is more flexible.

The internet we use is required to follow a set of rules or protocols about the format of data sent with the local network or the internet. This is called “Internet Protocol” or, more commonly, IP Address. This IP address may use either classful or classless addressing. We will go through the process of how each addressing system works and the differences between the two.

Jess here. I made 6-Figures in IT without needing a degree. If you like my blog, you can support it by checking out my progress to $188k per year in tech. (P.S. Now, I work remotely.)

Classful Addressing

Classful addressing or classful routing is a network routing system where all the available IP addresses are divided into five classes: A, B, C, D and E. This system was initially the only method of IP addressing.

Because IP addresses can only belong to any of the five classes, classful addressing leaves no room for flexibility. For example, if an internet provider requires a high number of host machines as provided by Class C but only a few host addresses as provided by Class B, the provider will have to opt for Class C with unused host addresses available.

Classful routing is divided into three parts which make it send the complete network address rather than sending subnet information. The router supplies its own subnet masks based on the locally configured subnets.

Classless Addressing

Classless addressing system is a revised IP addressing system. It has been introduced as a more efficient alternative to classful addressing.

Also known as Classless Inter-Domain Routing (CIDR), classless routing works by allocating and specifying the internet addresses more flexibly. Instead of the original Internet Protocol (IP) address classes, it uses inter-domain routing.

For example, think about the internet provider’s problem with the classful routing when there is a mismatch between the number of host machines and host addresses needed. The problem can be solved with classless addressing.

Classless addressing thus effectively solved the problems of classful addressing by providing a new and more flexible way to specify network addresses in routers. This allows internet providers to buy the exact amount necessary and avoid wastage of host addresses.

Differences Between Classful And Classless Addressing

Classless addressing came years after the invention of classful addressing. So we can think of classless routing as an improved and revised version of the classful addressing system.

In every feature where classless routing differs from classful routing, it brings more efficiency. Let’s look at the main differences between classful and classless routing.


VLMS or Variable Length Subnet Mask is not supported in classful routing. But it is available in classless routing. Thus, in classless addressing, subnet masks can change in the topology which is not possible in classful addressing.


Classless Inter-Domain Routing (CIDR) is not supported in classful addressing but available in classless addressing. This allows classless addressing to have variety in the number host machine and host addresses instead of a few fixed classes.

Subnet Mask

Classful routing does not import subnet masks and does not display subnets in other major subnets. While in classless routing, subnet masks are imported, and the subnets are displayed in other major subnets.

Address Division

In classful routing, the address is divided into three parts which are the Network, Subnet and Host. The classless addressing system is divided into two parts which are the Subnet and Host. Thus, classful addressing can only send the complete network address.

Bandwidth Requirement

Classful addressing requires more bandwidth than classless addressing. This makes the classful routing system slower and comparatively more costly.


Because the classful addressing system is divided into three parts, troubleshooting and detecting problems is easier. Troubleshooting in classless routing is much trickier and complicated.


In classful addressing, updates are regular or periodic, while updates in classless addressing systems are triggered updates.

So in most aspects, classless addressing is a much more efficient system. There are comparatively more advantages to using the classless addressing system.

Advantages Of Classless Addressing

Classless addressing has advantages over the classful addressing system since it was designed to solve the shortcomings of classful routing. The advantages of using classless addressing are:

  • The address space provided by the classless addressing is more efficient than the classful addressing.
  • In classless addressing, memory is allocated in the form of bits and bytes making it faster than classful routing, which stores a chunk of contiguous memory.
  • The class imbalance between hosts is solved in the classless addressing system
  • Classless addressing system does not require any separate entities for subnetting. So the subnet mask can change in the topology.
  • Classless addressing is flexible and has more efficient routing entries.

Problems With Classful Addressing

Classful addressing only provides IP addresses belonging to one of the five classes. The problems with each of these classes are:

Class A. There are millions of class A addresses wasted since the host ratios are very impractical.

Class B. Similarly, multiple class B addresses are wasted.

Class C. The number of addresses provided in class C is very small. So it fails to cater the needs of most institutions.

Class D. Multicast routing is the only option for class D, which means that the addresses are available as a single block only.

Class E. The IP addresses in this class are reserved.

The most concerning problem with the classful routing system was that it was running out of addresses very quickly due to the huge wastage of addresses in most classes. Classless routing was introduced in 1993 and solved this problem by its Classless Inter-Domain Routing (CIDR) system.

Classful addressing has become almost obsolete. Because of the shortcomings in almost all aspects of classful addressing, the classless routing system has become the popular choice. So the classless addressing system is the usual IP addressing currently.

Recent Posts