CCNA - VLSM Basics

Summary

This script explains the concept of Variable Length Subnet Masking (VLSM), which allows for the creation of subnets of varying sizes without overlapping address ranges. It demonstrates how a single network can be divided into equal-sized subnets and then further subdivided into smaller ones without infringing on existing subnets. VLSM provides flexibility in network design, enabling subnets to be tailored to specific needs rather than adhering to a strict power-of-two sizing.

Takeaways

• 😀 Subnets do not have to be of equal sizes as long as their address ranges do not overlap.
• 🔍 VLSM (Variable Length Subnet Masks) allows for the creation of subnets of different sizes.
• 📏 It is easier to create subnets by starting from larger ones and then dividing them into smaller subnets.
• 🌐 A network, such as 192.168.1.0/24, can be subdivided into smaller subnets, like /26, creating four equal-sized subnets.
• 📊 With VLSM, you can further subdivide one of these subnets into even smaller subnets, such as breaking a /26 subnet into two /27 subnets.
• ⚖️ VLSM provides the flexibility to create subnets of different sizes, based on the network's needs, without violating address space boundaries.
• 🧮 In this example, dividing a subnet into two /27 subnets results in one network with five total subnets.
• 📉 Three of the subnets will have 64 hosts each, and the two smaller ones will have 32 hosts each.
• 🔐 The key to using VLSM is ensuring that no subnets intrude into each other's address spaces.
• 💡 VLSM helps escape the limitation of equal-sized subnets, offering more flexibility in network design.

Q & A

What does VLSM stand for and how does it differ from traditional subnetting?

VLSM stands for Variable Length Subnet Masking. Unlike traditional subnetting, where all subnets must be the same size, VLSM allows for the creation of subnets with different sizes, provided that their address ranges do not overlap.

How does VLSM increase flexibility in network design?

VLSM increases flexibility by allowing network designers to create subnets of varying sizes based on the specific needs of different segments, rather than being restricted to equal-sized subnets.

What is the benefit of working from larger to smaller subnets when using VLSM?

Working from larger to smaller subnets ensures that address ranges are allocated efficiently, reducing the risk of overlap and ensuring that all necessary subnets fit within the available address space.

How are the address ranges affected when creating four subnets from a /24 network using a /26 subnet mask?

When creating four subnets from a /24 network using a /26 subnet mask, the subnets are created in increments of 64 IP addresses each. This results in four equal-sized subnets.

How does VLSM handle further subdividing one of the subnets from a /26 mask?

VLSM allows further subdivision by using a smaller subnet mask. For example, a /26 subnet can be subdivided into two /27 subnets, each with 32 IP addresses.