Classless Addressing (Part 2)

Summary

This lecture introduces the concept of classless addressing, also known as CIDR, which overcomes the limitations of classful addressing by allowing for more flexible and efficient IP address allocation. The session explains the drawbacks of classful addressing and demonstrates how classless addressing enables the creation of custom subnet masks, optimizing IP address usage. The importance of subnetting in achieving classless addressing is highlighted, and an activity is conducted to differentiate between valid and invalid subnet masks, emphasizing the need for consecutive ones followed by zeros in subnet masks. The lecture concludes with a homework question to reinforce the understanding of subnet masks.

Takeaways

• 😀 The session is focused on understanding the need for classless addressing and identifying valid and invalid subnet masks.
• 📚 Classful addressing has been replaced by classless addressing due to its drawbacks, such as lack of address flexibility, inefficient use of address space, and proliferation of router table entries.
• 🔍 Classless addressing, formally known as Classless Inter-Domain Routing (CIDR), allows for more efficient allocation of IPv4 addresses by breaking the constraints of class-based addressing.
• 💡 Subnetting is a crucial concept in computer networking that enables the creation of classless addressing and allows for the customization of network sizes based on device requirements.
• 🌐 In classless addressing, subnet masks can be customized to fit the needs of the network, rather than being limited to class A, B, or C subnet masks.
• 🔑 A valid subnet mask consists of consecutive binary '1's followed by consecutive '0's, with no mixture of ones and zeros in between.
• 📈 Subnet masks can be represented in decimal format, binary format, or using the slash notation, which indicates the number of consecutive '1's at the start of the mask.
• 📝 The script provides an activity to practice identifying valid and invalid subnet masks by converting decimal subnet masks to binary and analyzing their structure.
• 🚫 Invalid subnet masks have a mixture of ones and zeros that are not consecutive, which breaks the rule of continuous '1's followed by continuous '0's.
• 🎓 The lecture concludes with a homework question that challenges learners to apply their understanding of subnet masks to identify invalid options from a given list.
• 👋 The presenter encourages engagement by asking viewers to solve the homework problem and share their answers in the comment section.

Q & A

What are the five classes of IPv4 addresses?

There are five classes of IPv4 addresses: Class A, B, C, D, and E. Class D is used for multicast purposes, and Class E is reserved for experimental and research purposes.

Why is there a shift from classful to classless addressing?

The shift from classful to classless addressing is due to the drawbacks of classful addressing, which include lack of internal address flexibility, inefficient use of address space, and the proliferation of router table entries.

What is the formal name of classless addressing?

The formal name of classless addressing is Classless Interdomain Routing, pronounced as CIDR.

How does classless addressing help in the allocation of IPv4 addresses?

Classless addressing allows service providers to allocate IPv4 addresses on any address bit boundary, known as the prefix length, rather than being restricted to Class A, B, or C boundaries.

What is the significance of subnetting in classless addressing?

Subnetting is significant in classless addressing as it enables the creation of classless addressing and facilitates the creation of networks with a specific number of devices, allowing for the efficient use of IP addresses.

What are the possible values for a subnet mask octet?

A subnet mask octet can take values such as 255, 254, 252, 248, 240, 224, 192, 128, or 0.

What is the rule for the arrangement of bits in a valid subnet mask?

In a valid subnet mask, there must be a consecutive sequence of ones followed by a consecutive sequence of zeros, with no mixture of ones and zeros in between.

How can a subnet mask be represented?

A subnet mask can be represented in decimal format, binary format, or using slash notation.

What does a slash notation of 24 in a subnet mask signify?

A slash notation of 24 signifies that there are 24 consecutive ones in the subnet mask, followed by 8 zeros, which corresponds to a class C subnet mask.

What is the purpose of the activity involving the conversion of subnet masks from decimal to binary?

The purpose of the activity is to help learners understand how to identify valid and invalid subnet masks by analyzing the binary representation for the correct sequence of ones and zeros.

What is the homework question asked at the end of the session?

The homework question is to identify the invalid subnet mask from the following options: 255.240.0.0, 248.0.0.0, 255.255.128.0, 255.255.255.252, and 255.255.242.0.

Outlines

00:00

😀 Classless Addressing Overview and Objectives

This paragraph introduces the second part of a class on classless addressing, setting the stage for the session's learning outcomes. The learner is expected to understand the necessity of classless addressing and to discern valid from invalid subnet masks through an activity. The paragraph explains the transition from classful to classless addressing due to the drawbacks of classful addressing, such as lack of address flexibility and inefficient use of address space. It also introduces the concept of Classless Interdomain Routing (CIDR) and its advantages in allocating IPv4 addresses more efficiently, avoiding waste and enabling the creation of custom subnet masks tailored to network requirements.

05:01

😎 Understanding Subnet Masks and CIDR Notation

The second paragraph delves into the specifics of subnet masks in the context of classless addressing. It explains the valid values a subnet mask can take and the importance of consecutive ones followed by zeros in the mask. The paragraph also discusses the representation of subnet masks in decimal, binary, and CIDR notation, providing examples to illustrate the concept. An activity is introduced to help learners identify valid and invalid subnet masks, with examples demonstrating the conversion of decimal subnet masks to binary and their corresponding CIDR notations. The paragraph concludes with a homework question that challenges learners to apply their understanding of subnet masks to identify invalid options.

10:01

🎉 Conclusion and Homework Assignment

The final paragraph wraps up the lecture with a summary of the key points covered, including the need for classless addressing and the identification of valid and invalid subnet masks. It encourages learners to complete the homework problem and share their answers in the comment section. The paragraph ends with a note of thanks and appreciation for the audience's engagement, signaling the end of the session with applause and music, creating a sense of closure and celebration of the learning experience.

Keywords

💡Classless Addressing

Classless Addressing, also known as Classless Interdomain Routing (CIDR), is a method that allows for a more flexible and efficient allocation of IPv4 addresses. It moves away from the traditional classful addressing system, which divided IP addresses into classes A, B, and C, each with a fixed number of addressable hosts. In the video, classless addressing is discussed as a solution to the drawbacks of classful addressing, such as the inefficient use of address space and lack of address flexibility. It enables the creation of custom subnet masks to better suit the needs of a network, thus conserving IP addresses.

💡Subnet Mask

A subnet mask is a 32-bit number that divides the IP address into network and host portions, defining the boundary of a network. In the context of the video, subnet masks are crucial for implementing classless addressing as they determine the size of the network and the number of available host addresses. The script explains that a valid subnet mask contains consecutive bits set to '1' followed by consecutive bits set to '0', and provides examples of valid and invalid subnet masks.

💡IPv4

IPv4, or Internet Protocol version 4, is the fourth version of the Internet Protocol and is the most widely used networking protocol for the Internet. It provides the means for devices to communicate over the network by assigning each device a unique IP address. The video discusses the limitations of IPv4, particularly in the context of classful addressing, and the transition to classless addressing to better manage the finite number of IPv4 addresses available.

💡Classful Addressing

Classful addressing is the traditional system of IP address allocation where addresses are divided into classes (A, B, C, D, and E) based on the first octet of the IP address. This system has limitations, as discussed in the video, such as the fixed number of host addresses in each class, leading to inefficiencies in address allocation. The video script contrasts classful addressing with classless addressing, highlighting the need for the latter due to the drawbacks of the former.

💡CIDR Notation

CIDR notation is a way of representing subnet masks using a forward slash ('/') followed by a number that indicates the number of bits set to '1' in the subnet mask. This notation simplifies the representation of subnet masks and is used in the video to illustrate different subnet sizes. For example, a 'slash 24' in CIDR notation corresponds to a subnet mask of 255.255.255.0, indicating that the first 24 bits of the IP address are used for the network portion.

💡Subnetting

Subnetting is the process of dividing a network into smaller networks, known as subnets. This is done to improve the management and efficiency of IP addresses within a network. In the video, subnetting is mentioned as a key technique that facilitates the implementation of classless addressing, allowing for the creation of custom subnet masks to suit specific network requirements.

💡IP Address

An IP address is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. In the video, IP addresses are discussed in the context of classful and classless addressing, emphasizing the importance of understanding how these addresses are allocated and managed within a network.

💡Binary Representation

Binary representation is the way of writing numbers using only two symbols, 0 and 1. In the context of the video, binary representation is used to illustrate the structure of subnet masks and to determine their validity. The script explains that a valid subnet mask in binary form will have consecutive '1's followed by consecutive '0's, with no mixture of the two in between.

💡Network Layer

The network layer is a layer in the OSI model that is responsible for the transmission of data between devices on different networks. In the video, the network layer is mentioned in relation to subnetting and classless addressing, which are techniques used at this layer to manage and route data efficiently across a network.

💡Slash Notation

Slash notation, as discussed in the video, is a shorthand way of writing subnet masks using CIDR notation. It is a quick way to denote the number of continuous '1's in the subnet mask. For example, a 'slash 19' subnet mask means that there are 19 consecutive '1's in the mask, followed by '0's, making it a more concise way to express subnet masks than the traditional dotted decimal notation.

💡Homework Problem

The homework problem presented in the video script is an exercise for the learners to apply their understanding of valid and invalid subnet masks. It provides a list of subnet masks and asks learners to identify which ones are invalid, reinforcing the concepts taught in the lecture about the structure and rules for subnet masks.

Highlights

Introduction to classless addressing and its benefits over classful addressing.

Classful addressing limitations: lack of address flexibility, inefficient address space use, and router table proliferation.

Classless addressing, formally known as Classless Interdomain Routing (CIDR), allows for more efficient IP address allocation.

Class A, B, and C IP addresses are the primary classes used, with D and E reserved for multicast and experimental purposes.

The necessity of moving from classful to classless addressing due to IP address wastage.

Subnetting as a key concept in enabling classless addressing and efficient network design.

Explanation of how subnet masks function in a network to identify devices and neighbors.

Subnet masks can take eight specific values and must have consecutive bits set to 1 followed by zeros.

Binary representation of subnet masks and the importance of consecutive ones and zeros.

Different ways to represent subnet masks: decimal, binary, and slash notation.

Understanding slash notation and its relation to subnet mask values.

Class A, B, and C subnet masks and their corresponding slash notations.

Activity to identify valid and invalid subnet masks using decimal and binary conversions.

Analysis of provided subnet masks to determine their validity based on the rules of consecutive bits.

Homework problem presented to engage learners in identifying invalid subnet masks.

Summary of the lecture's key points and the importance of understanding classless addressing.

Conclusion and call to action for viewers to participate in the homework problem and comment their answers.

Transcripts

we are now in part two of classless

addressing let's start the session with

the outcomes

upon the completion of this session the

learner will be able to outcome number

one we will understand the need for

classless addressing and outcome number

two we will identify the valid and

invalid subnet mask with the help of an

activity let's start the session with

the classful addressing we know

basically there are five classes in ipv4

addresses class a b c d and e class d

for multicast purpose and class e is for

experimental and research purpose so we

are left with only class a b and c for

our usage and we have already seen in

the previous lecture that classful

addressing based ip addresses and that's

why we are migrating from class full

addressing to classless addressing we

have some drawbacks with classful

addressing the drawbacks include the

lack of internal address flexibility the

inefficient use of address space and the

proliferation of router table entries we

have elaborately discussed about this in

the previous lecture that is in part one

of classless addressing if you are not

clear with the drawbacks i request you

to watch my previous lecture titled

classless addressing part one we are

clear that classful addressing vast ip

addresses and that's why we are focusing

on classless addressing

the formal name of classless addressing

is classless interdomain routing it is

cider cidr it is pronounced as cider

why do we need decider or classless

addressing it created a new set of

standards that allowed service providers

to allocate ipv4 addresses on any

address bit boundary that is the prefix

length instead of only by a class a b or

c we know basically the class a b and c

are used for our purpose but when we go

with class a b or c there are chances

for the ip addresses getting wasted and

that's why we are moving towards

classless in classless addressing we can

create our own set of standards that is

we can create a new subnet mask where

this new subnet mask can help us to

determine how many devices are needed

for our network so that it enable us to

sparingly use the ip addresses rather

wasting a huge set of ip addresses so

this classless addressing is possible

with the help of subnetting there is an

important topic in computer networks the

two in network layer which is the

subnetting so subnetting helps us to

create classless addressing and it also

facilitates us to create our own network

with the number of devices we need we

will talk about the subnetting

elaborately in the upcoming lectures but

before going into the subnetting topic

we need to know the subnet mask ip

address says who are you in the network

and subnet mask says who are your

neighbors in your network let's see the

valid subnet mask so a subnet mask will

take only these eight possible values

there are basically four octets in an ip

address likewise there are four octets

in a subnet mask as well say if it is a

class a subnet mask it will be

255.0.0.0.

if it is class b it is 255.255.0.0

if it is class c it is 255.255.255.0

but we are going to create our own

subnet mask based on our need and

requirement isn't it so these are the

values that is possible in a subnet mask

an octet value can be 255 or 254 252 248

240 224 192 128 or even zero so how can

we know this in a subnet mask there will

be a consecutive ones followed by

consecutive zeros so there will not be a

mixture of zeros and ones always

remember this point in a subnet mask

there will be consecutive ones followed

by consecutive zeros say we have already

witnessed this in a classful addressing

also say if it is a class b subnet mask

what will be the subnet value it will be

255.255.0.0

when it is two five five two five five

zero zero when we write it in binary we

will get a continuous 16 once followed

by continuous 16 zeros right so that's a

valid subnet mask let's see more about

this in the upcoming slide we already

know a subnet mask can be represented

either in the decimal format or in the

binary format or even it can be

represented using a slash notation so

this is the slash notation when it is

slash one what does it mean it means

only one one is there followed by

continuous zeros i will explain this

when it is slash one there is only one

one in the binary notation so this is a

valid subnet mask um what is the decimal

equivalent for this 1 means it's 128 so

the first octet is 128 and there are no

ones in the other places obviously this

is 128.0.0.0.

and what about the second example that

is slash two slash two means there are

two ones followed by six zeros in the

first octet and obviously there will be

remaining zeros in the other octet as i

mentioned once followed by continuous

zeros and there will not be mixture of

zeros and ones in any octane so if it is

a one it will be continued and then a

zero is started it will be continued

till the last so this is an example

slash two notation a slash 2 means what

is the equivalent decimal notation slash

2 means it's 128 plus 64 the bit

position values it is 128 plus 64. it is

192. so this is

192.0.0.0. so 192.0.0.0

let's take slash three slash three means

it's three ones followed by 29 zeros

three ones means it's 128 plus 64 plus

32 which is 224 and the remaining three

octets are zero how many bit values are

there in subnet mask in ipv4 we know

there are 32 bits so the subnet mask is

also of 32 bit so it can be from slash 1

to slash 32 slash 1

slash three slash four up two slash

thirty two is possible and we know slash

eight means it's class full of

addressing it is class a subnet mask

slash sixteen means it's class b subnet

mask and slash twenty four means it's

class c subnet mask and that's why it's

mentioned in a different color let's

take another example it is slash 19.

slash 19 means 19 ones followed by zeros

so how many zero values so out of 32

there are 19 ones so this is eight right

first octet is of eight bits so we are

putting eight ones another eight ones in

the second octet so eight plus eight is

sixteen so sixteen plus three is

nineteen so we are putting three ones in

the third octave so we have 19 ones and

followed by 13 zeros so we are clear

that there are consecutive ones followed

by consecutive zeros so slash 30 means

30 ones and two zeros let's see an

activity it will be more clear for you

to understand the valid and invalid

subnet mask

so the subnet mask in decimal is given

and we are required to find whether they

are valid or invalid let's take the

first example which is 255.255.255.240.

let's convert this into binary so we

have the binary representation of the

decimal subnet mask mentioned here so

when we convert this into binary we can

see its continuous once followed by

zeros so there is no mixture of zeros

and ones in between so obviously this is

a valid subnet mask so we can say this

is a valid subnet mask and what is the

slash notation eight ones eight ones

eight ones and here four ones

so eight plus eight plus eight is twenty

four twenty five twenty six twenty seven

twenty eight so this is slash twenty

eight perfect let's take the second one

which is two five five or two thirty or

two fifty five dot zero when we convert

this into binary we are ending up with

this binary value so obviously this is

not a valid subnet mask because we know

a continuous once when a 0 is started it

should continue till the last if we

notice here a 0 has started and then

still we have wants and zeros

combinations it's obviously an invalid

subnet mask and we can't give a slash

notation for this let's convert the

binary equivalent for all the subnet

mask we have the binary representation

of all the subnet masks now let's

analyze whether it is valid it's

obviously valid because continuous ones

if a zero is started continuous zeros

are there and no one is interrupting

after that so obviously this is valid

and it's slash 16 it's a class b subnet

mask why there are 16 ones then

240.0.0.0

yes it is also valid four ones followed

by remaining zeros it is valid subnet

mask it's a slash four subnet mask right

then coming to the next one it's 223.0

when we convert this into binary we are

ending up with continuous ones followed

by a zero and then it should be all

zeros right if it is valid but here we

are finding one so it is obviously

invalid and coming to the last one it's

255.0.255.0 so we are ending up with

once

again zeros and then one is interrupting

right so it should not be the case if it

is a valid subnet mask so the last

subnet mask mentioned here is also

invalid

let's see the homework question

identify the invalid subnet mask from

the following option yay 255.240.0.0

option b 248.0.0.0

option c 255.255.128.0

option d 255.255.255.252

and option e 255.255.242.0

solve this question and post your answer

in the comment section

and that's it guys i hope now you

understood the need for classless

addressing and we also identified valid

and invalid subnet mask with the help of

an activity don't forget about the

homework problem i hope you guys enjoyed

the lecture and thank you for watching

[Applause]

[Music]