There are two types of Subnetting: FLSM and VLSM. In FLSM, all subnets have an equal number of host addresses and use the same subnet mask. In VLSM, subnets have a flexible number of host addresses. They use a subnet mask based on the number of hosts.
Default IP subnets have a large number of IP addresses. Most networks do not need too many IP addresses. If they use the default subnet, all unused IP addresses become useless. To utilize free IP addresses, we use subnetting.
Subnetting allows us to break default IP subnets. There are two types of subnetting: FLSM and VLSM.
FLSM stands for Fixed Length Subnet Mask. In it, we break the default IP subnet into the same-sized subnets. For example, if the default subnet has 12 IP addresses, we can break it into three equal-sized subnets having 4 IP addresses in each.
VLSM stands for Variable Length Subnet Mask. In it, we break the default IP subnet into subnets having various sizes. For example, if the default subnet has 12 IP addresses, we can break it into two subnets where the first subnet has 8 IP addresses and the second subnet has 4 IP addresses.
Differences between FLSM Subnetting and VLSM Subnetting
The following table lists the differences between FLSM and VLSM.
| FLSM (Fixed Length Subnet Masks) Subnetting | VLSM (Variable Length Subnet Masks) Subnetting |
| All subnets are equal in size. | Subnets are variable in length. |
| All subnets have an equal number of hosts. | Subnets have a variable number of hosts. |
| All subnets use the same subnet mask. | Subnets use different subnet masks. |
| It is easy to configure and manage. | It is complex in configuration and administration. |
| It wastes a lot of IP addresses. | It wastes minimum IP addresses. |
| It is also known as classful subnetting. | It is also known as classless subnetting. |
| It supports both classful and classless routing protocols. | It supports only classless routing protocols. |
This tutorial is the eighth chapter of the tutorial series. Other chapters of this series are the following.
Chapter 01 Introduction to Subnetting
Chapter 02 Network Address Basic Concepts Explained with Examples
Chapter 03 The Subnet Mask and Slash Notation
Chapter 04 Convert Decimal IP address in Binary and Binary in Decimal
Chapter 05 Basic Subnetting in Computer Networks Explained
Chapter 06 Subnetting Tutorial - Subnetting Explained with Examples
Chapter 07 Subnetting Tricks Subnetting Made Easy with Examples
Chapter 09 VLSM Subnetting Explained with Examples
Chapter 10 VLSM Subnetting Examples and Calculation Explained
Chapter 11 Route Summarization Advantages and Disadvantages
Chapter 12 Supernetting Tutorial: - Supernetting Explained with Examples
