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.

Outlines

00:00

🧑‍💻 Introduction to VLSM and Subnetting Basics

This paragraph introduces the concept of VLSM (Variable Length Subnet Mask). The key idea is that subnets do not need to be of equal size, as long as their address ranges do not overlap. The paragraph explains that unequal-sized subnets can be created, providing flexibility for network designs. It highlights the importance of working from larger to smaller subnets, using an example of subnetting a /24 network into four equal-sized subnets using a /26 mask. This sets up the foundation for understanding how VLSM allows for more flexible subnetting.

🔄 Modifying Subnets with VLSM

In this section, the concept of modifying an existing subnet using VLSM is discussed. The example of subnetting the 192.168.1.192/26 network is presented, where the subnet range is from 192 to 255. The paragraph explains how VLSM can be applied to divide this address space into two smaller subnets, each using a /27 mask. This creates a total of five subnets—three with 64 hosts each, and two with 32 hosts each—demonstrating how VLSM offers flexibility in subnet size without overlapping address spaces.

🚀 Flexibility with VLSM

This paragraph concludes by emphasizing the power and flexibility that VLSM provides in subnetting. It highlights how VLSM allows network administrators to escape the traditional limitation of creating subnets in powers of two, which previously forced all subnets to be of equal size. With VLSM, subnets can be tailored to specific needs, allowing for greater optimization of address space based on network requirements. This flexibility is key to efficient IP management in modern network designs.

Keywords

💡VLSM (Variable Length Subnet Mask)

VLSM allows for the creation of subnets of different sizes within the same network. In the video, VLSM is the main concept being discussed, as it gives network administrators the flexibility to create subnets that fit the specific size needs of a network without wasting IP address space. It is demonstrated by subdividing a larger subnet into smaller ones while ensuring no address overlap.

💡Subnet

A subnet is a segmented portion of a larger network. In this video, the speaker explains how subnets can be created using VLSM and highlights how they can vary in size. For example, the network 192.168.1.0/24 is subnetted into four smaller subnets using a /26 mask, and then one of those subnets is further divided.

💡/24 Network

A /24 network refers to a network where 24 bits are used for the network portion of the IP address, leaving 8 bits for host addresses. The video begins with the speaker discussing a 192.168.1.0/24 network and how it can be subnetted into smaller sections, demonstrating how the number of available IP addresses decreases with subnetting.

💡/26 Subnet Mask

A /26 subnet mask uses 26 bits for the network portion, leaving 6 bits for host addresses. This creates subnets with 64 IP addresses each. In the video, the speaker initially subdivides the 192.168.1.0/24 network into four /26 subnets, each providing 64 IP addresses.

💡Subnetting

Subnetting is the process of dividing a larger network into smaller, more manageable subnets. The speaker demonstrates subnetting by splitting a /24 network into smaller /26 subnets and later explains how VLSM can be used to create subnets of varying sizes to meet different requirements.

💡Address Range

An address range refers to the set of IP addresses available within a subnet. The video explains that when subnetting, it is crucial to ensure that the address ranges of different subnets do not overlap. For example, the address range for 192.168.1.192/26 goes from 192.168.1.192 to 192.168.1.255.

💡Overlapping Subnets

Overlapping subnets occur when two subnets share some of the same IP address range. In the video, the speaker emphasizes that when using VLSM, care must be taken to ensure that newly created subnets do not overlap with existing ones. This is a key aspect of managing IP addresses efficiently.

💡/27 Subnet Mask

A /27 subnet mask uses 27 bits for the network portion, leaving 5 bits for host addresses, which results in 32 available IP addresses. In the video, the speaker takes one of the /26 subnets and further divides it into two /27 subnets, creating smaller networks with 32 addresses each.

💡Host Addresses

Host addresses are the IP addresses assigned to devices within a subnet. The size of the subnet mask determines how many host addresses are available in that subnet. For example, a /26 subnet has 64 available host addresses, while a /27 subnet has 32. The speaker uses this concept to illustrate how VLSM allows for the efficient allocation of IP addresses.

💡Powers of Two

Powers of two refer to the fact that the number of IP addresses in a subnet is always a power of two. In the video, the speaker explains that VLSM allows subnetting beyond the traditional constraints of powers of two by enabling subnets of different sizes to be created based on need. This flexibility is contrasted with the limitations of equal-sized subnetting.

Highlights

VLSM allows the creation of unequal-sized subnets as long as their address ranges do not overlap.

Subnets do not all need to be the same size when using VLSM.

It is easier to work from larger to smaller subnets when creating subnets.

Starting with a 192.168.1.0/24 network, you can subnet it into four /26 subnets, which increases by 64 in address space.

With VLSM, you can take one of the existing subnets and further divide it into smaller subnets.

Subnets created using VLSM should not intrude into other subnets’ address spaces.

An example: take the 192.168.1.192/26 subnet, and divide it into two /27 subnets.

Dividing a /26 subnet into two /27 subnets gives you two subnets with 32 hosts each.

The remaining three subnets in the original example remain with 64 hosts each.

VLSM allows you to create five subnets from the original four by subdividing one into smaller segments.

The flexibility of VLSM escapes the equal-sized subnet limitation of traditional subnetting.

VLSM enables subnetting in a more flexible manner based on network requirements.

This approach allows the creation of subnets in powers of two, but with varying sizes.

The main advantage of VLSM is being able to allocate IP addresses more efficiently, avoiding wasted addresses.

VLSM is a method that enhances network design flexibility by using variable length subnet masks.

Transcripts

the basics of vlsm or variable length

subnet masks works like this

one subnets do not have to be equal

sizes as long as their address ranges do

not overlap so we can create unequal

sized subnets they do not all have to be

the same size

two when creating subnets it is easier

to work from larger to smaller subnets

so for example i have the one nine two

one six eight one dot zero slash 24

network

i subnet the network into four subnets

slash 26 subnet masks

so the subnets go up by 64. i now have

four equal sized subnets

with vlsm or variable length subnet

masks

i can decide that i want to change one

of these subnets and further subdivide

them into smaller subnets as long as the

address spaces that i create or the

subnets that i create

do not intrude into the other subnets

for instance i could take this 192 168

1.192 subnet the address range for this

subnet goes from 192 all the way up to

255.

what i can do is is i can say

instead of having this subnet slash 26

what if i

take that address space and divide it

into two smaller subnets size 27 each

if i do this i effectively have created

five subnets

the three subnets up here are 64 hosts

each

and the two new subnets that i created

from the fourth subnet are 32 hosts each

the reason i can do this is because my

two smaller subnets do not intrude into

the larger subnets

this is variable length subnet masks

in this situation it has also allowed me

to create five subnets

thus escaping the equal sized subnet

limitation of creating subnets in powers

of two this gives me greater flexibility

and allows me to create subnets of

different sizes based on the

requirements of my network