Subnetting (Solved Problem 6)

Summary

This educational video script explains how to determine the limited broadcast address in a subnet using two methods. First, it introduces the reverse engineering method, starting with a Class B subnet mask of 255.255.0.0, and identifying the network and broadcast addresses for the subnet. The second method involves a bitwise OR operation after taking the one's complement of the subnet mask. The script uses the example of an IP address 25.34.12.56 with a /16 subnet mask to demonstrate the process, resulting in a broadcast address of 25.34.255.255. The lecture concludes with a homework question involving an IP address range and asks viewers to find the broadcast address.

Takeaways

• 😀 The video script discusses subnetting, specifically finding the broadcast address in a block of addresses.
• 🔍 The example uses an IP address of 25.34.12.56 with a subnet mask represented in slash notation as /16.
• 📚 The subnet mask /16 is equivalent to 255.255.0.0 in decimal, which is a Class B subnet mask.
• 👉 The reverse engineering method starts with the subnet mask and involves converting it into binary to find the network range.
• 💡 The first subnet range is calculated to be from 25.34.0.0 to 25.34.255.255, using the subnet mask.
• 🎯 The given IP address falls within the first subnet, and the last address of this subnet is the broadcast address.
• 🛠️ For finding the broadcast address, a bitwise OR operation is used after taking the one's complement of the subnet mask.
• 📝 The process involves converting the IP address and the inverted subnet mask into binary and performing the OR operation.
• 🔢 The result of the OR operation gives the broadcast address in binary, which is then converted back to decimal to find 25.34.255.255.
• 📚 The video also mentions a homework question asking to find the broadcast address for an IP block with an address range of 182.44.82.16-26.
• 👏 The lecture concludes with a recap of the process and an encouragement for viewers to apply the knowledge to solve the homework question.

Q & A

What is the IP address given in the script?

The IP address given in the script is 25.34.12.56.

What is the subnet mask notation used in the script?

The subnet mask notation used in the script is slash 16, which is equivalent to 255.255.0.0 in decimal.

What is the reverse engineering method mentioned in the script?

The reverse engineering method starts with the subnet mask and involves converting it to binary, identifying the subnet generator, and determining the network ranges.

What is the subnet generator in the given subnet mask?

The subnet generator in the given subnet mask is 1, and it is located in the second octet.

How is the first subnet range determined in the script?

The first subnet range is determined by using the network address 25.34.0.0 and the broadcast address 25.34.255.255.

What is the difference between finding the network address and the broadcast address in terms of bitwise operations?

For finding the network address, a bitwise AND operation is used, whereas for finding the broadcast address, a bitwise OR operation is used after performing the subnet mask complement.

Why is the subnet mask complement necessary before finding the broadcast address?

The subnet mask complement is necessary to convert all ones to zeros and all zeros to ones in the subnet mask, which is then used in the bitwise OR operation to determine the broadcast address.

What is the broadcast address of the subnet where the given IP address resides?

The broadcast address of the subnet where the given IP address 25.34.12.56 resides is 25.34.255.255.

How does the bitwise OR operation work in determining the broadcast address?

The bitwise OR operation sets an output bit to 1 if at least one of the input bits is 1, resulting in the broadcast address when applied to the IP address and the complemented subnet mask.

What is the homework question presented in the script?

The homework question asks to find the last address, which is the limited broadcast address, in a block of addresses where the IP address of one host is 182.44.82.16-26.

Outlines

00:00

🔍 Reverse Engineering to Find Broadcast Address

The video script begins with an exploration of subnetting, specifically focusing on identifying the broadcast address for a given IP address and subnet mask. The IP address provided is 25.34.12.56, and the subnet mask is represented in slash notation as /16, which translates to 255.255.0.0 in decimal. The method used to find the broadcast address involves reverse engineering, starting with the subnet mask and converting it into binary to determine the network's range. The first subnet is identified as 25.34.0.0 to 25.34.255.255. The script explains that the last address in this range, 25.34.255.255, is the broadcast address for the subnet. Additionally, a formal method is introduced, which involves using a bitwise OR operation after taking the one's complement of the subnet mask. This process is crucial for understanding how to calculate the broadcast address in networking.

05:00

📚 Step-by-Step Guide to Calculate Broadcast Address

The second paragraph of the script provides a step-by-step guide on how to calculate the broadcast address using the bitwise OR operation. It starts with taking the given IP address, converting it into binary, and then bringing in the subnet mask, which is /16 or 255.255.0.0. The key step introduced here is the one's complement of the subnet mask, which involves inverting all bits (changing 1s to 0s and vice versa). This complemented subnet mask is then used in the bitwise OR operation with the binary representation of the IP address to find the broadcast address. The operation is explained with examples, demonstrating how the presence of a '1' in either input results in a '1' in the output. The final result of this operation for the given IP address is 25.34.255.255, confirming the broadcast address. The script concludes with a homework question that asks the viewer to find the broadcast address for a different IP address range, 182.44.82.16-26, encouraging practical application of the concepts learned.

Keywords

💡Subnetting

Subnetting is the process of dividing a network into smaller sub-networks. It is a key concept in network design that allows for efficient allocation of IP addresses and better management of network traffic. In the video's context, subnetting is used to determine the range of IP addresses available within a specific network block, which is essential for understanding the network's structure and capacity.

💡IP Address

An IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. In the video, the IP address '25.34.12.56' is provided as an example to demonstrate how to find the broadcast address within a subnet. The IP address is crucial for identifying and locating devices within a network.

💡Subnet Mask

A subnet mask is a 32-bit number used in networking to divide the IP address into network and host portions. It helps in identifying the subnet to which a device belongs. In the script, the subnet mask is represented in slash notation as '/16', which translates to '255.255.0.0' in decimal. This mask is fundamental in determining the network and broadcast addresses.

💡Slash Notation

Slash notation, often represented as /x, where x is a number, is a shorthand used to denote the subnet mask in CIDR (Classless Inter-Domain Routing) format. In the video, 'slash 16' is used to denote that the first 16 bits of the IP address are used for the network part, and the remaining bits are for host addresses. This notation simplifies the representation of subnet masks.

💡Broadcast Address

The broadcast address is a special IP address used to send data to all hosts within a specific subnet. It is the last address in the range of addresses for a subnet. In the video, the task is to find the broadcast address for the subnet, which is essential for understanding how data is transmitted to all devices within a network segment.

💡Reverse Engineering Method

The reverse engineering method mentioned in the video is a technique used to determine network parameters by starting with known values such as the subnet mask and working backward to find other related network details. This method is applied to find the network and broadcast addresses, providing a practical approach to understanding subnetting.

💡Class B Subnet Mask

A Class B subnet mask is a type of subnet mask that is used in Class B networks, which are a category of IP addresses that start with the first two octets ranging from 128.0.0.0 to 191.255.0.0. In the script, '255.255.0.0' is identified as a Class B subnet mask, indicating that the first two octets define the network portion of the IP address.

💡Bitwise AND Operation

The bitwise AND operation is a fundamental operation in computer science that performs a logical AND on each bit of two binary numbers. In the context of the video, the bitwise AND operation is used to find the network address by combining the IP address and the subnet mask. This operation is crucial for determining the network part of an IP address.

💡Bitwise OR Operation

The bitwise OR operation is another fundamental operation that performs a logical OR on each bit of two binary numbers. In the video, the bitwise OR operation is used to find the broadcast address after taking the one's complement of the subnet mask. This operation helps in determining the broadcast address for a subnet.

💡One's Complement

One's complement is a binary operation where each bit of a number is inverted, turning 1s into 0s and 0s into 1s. In the script, the subnet mask is inverted (one's complement) before performing the bitwise OR operation to find the broadcast address. This step is essential for understanding how the broadcast address is calculated.

💡Homework Question

The homework question provided in the video script is an exercise for the viewers to apply the concepts learned in the lecture. It asks to find the broadcast address for a given IP address range, which tests the understanding of subnetting, IP addressing, and the use of subnet masks. This question reinforces the practical application of the concepts discussed in the video.

Highlights

The lecture discusses finding the limited broadcast address in a subnet using the reverse engineering method.

An example IP address 25.34.12.56 and subnet mask in slash notation /16 is used to illustrate the process.

The subnet mask is a Class B subnet mask, represented as 255.255.0.0 in decimal.

Binary conversion of the subnet mask reveals all ones in the first two octets and all zeros in the last two.

The subnet generator is identified as 1 in the second octet, with a decimal place of one.

Network ranges are created using the subnet generator and octet position, with the first subnet being from 25.34.0.0 to 25.34.255.255.

The given IP address falls within the first subnet, with the first address being the network address and the last being the broadcast address.

The broadcast address for the subnet is determined to be 25.34.255.255.

A formal method for finding the broadcast address involves using the bitwise OR operation.

Before the OR operation, the subnet mask must be inverted (ones complement) to find the broadcast address.

The bitwise OR operation is explained, where an output of one is produced if at least one input is one.

The process of converting the binary result back to decimal to find the broadcast address is demonstrated.

The importance of the subnet mask complement step before the OR operation is emphasized.

A homework question is presented, asking to find the broadcast address for an IP block with a given host IP address.

The lecture concludes with a summary of the steps and a reminder of the importance of the subnet mask complement.

The lecture includes a musical and applause segment, indicating the end of the presentation.

Transcripts

foreign

number six in subnetting

in a block of addresses we know the IP

address of one host is

25.34.12.56 and the subnet mask is

represented in a slash notation which is

slash 16. what is the last address that

is the limited broadcast address in this

block we have already solved this in the

previous lecture but in the previous

lecture we had intended to find the

network address but we are required to

find the broadcast address in this

lecture let's solve this first with the

reverse engineering method which we had

dealt in the previous case the reverse

engineering method starts with the

subnet mask we know the subnet mask is a

Class B subnet mask which is

255.255.0.0 when we convert this subnet

mask into binary we will be getting all

ones in the first two octets and all

zeros in the next two octets then where

is the first one we are encountering the

first one we are encountering in the

second octet right so in the second

octet the first one is here and what is

the decimal place of this first one when

we move from right to left the decimal

place of this one is exactly one so the

subnet generator is 1 and the octet

position is 2 right because this subnet

generator is in the second octet so the

subnet generator is equal to 1 and the

octet position is equal to 2 and we have

already created this network ranges I

had just copied from the previous

problem and I will paste it here we know

the first Subnet will be from 25 or

34.0.0 to

25.34.255.255 if you want to know how I

have generated this I request you to

watch the previous problem that is

solved problem number five now the IP

address which is mentioned in the

question is falling in the first Subnet

we know the first address is the network

address and the last address of the

subnet is the broadcast address so

obviously 25 or

34.255.255 is the broadcast address of

this subnet the IP address of one of the

hosts is given in the question and we

found out the broadcast address of this

entire net work right this is one way of

solving this and this way of solving the

problem is the reverse engineering

approach now we will solve this in a

formal way in the previous lecture we

have found the network address by using

a simple and operation that is the

bitwise and operation but for finding

the broadcast address in this problem we

are going to use the bitwise or

operation just see how I am going to do

this so first we need to take the IP

address which is given in the question

right the IP address which is given in

the question is 25 or

34.12.56 as usual we need to convert

this IP address into binary and we

converted this into binary now we need

to bring in the subnet mask and what is

this update mask that is mentioned in

this question

class 16 right slash 16 means we need to

fill in 16 ones here and then remaining

zeros let's fill that so we are bringing

in 16 ones here and 16 zeros here

because this is the slash 16 subnet mask

and the equivalent of slash 16 in

decimal is

255.255.0.0 in the previous problem we

just did and operation with these values

right now here one additional step the

additional step is before making the or

operation we need to do the mass

complement so this is the subnet mask we

need to do the subnet mask complement

complement means it's simple once

complement so here we will convert all

ones as zeros and all zeros as ones so

when we do that we'll be getting the

first two octets with full of zeros and

the last two octets is full of one

please note I am pinning this step here

it's a very important step we need to do

subnet mask complement before

progressing with the or operation in the

previous problem when we did a network

address calculation we didn't do this

complement operation simply we have

taken the IP address subnet mask

converted that into binary and performed

the bitwise and operation but here we

need to take the IP address first and

then we need to take the subnet mask and

then inverse the subnet mask that is

make one's complement to the subnet mask

so this is a very important step the

step is mass complement after we

complete this Mass complement as usual

we will start proceeding with the

operation the operation for finding the

broadcast address is the bitwise or

operation please note for finding the

network address we did and operation for

finding the broadcast address we need to

perform or operation now we will carry

out the bitwise or operation the bitwise

or operation is very simple when any one

of the inputs is one we will be getting

one as the output so if both the inputs

are 0 we'll be getting 0 as the output

for 0 0 will be getting 0 0 1 1 0 1 1

for these combinations will be getting

1. in this case we'll be getting this as

the result let's check it out now so

let's take the first octet and we'll

verify it so for 0 0 we'll be getting 0

for 0 0 it's zero zero zero it's zero

one zero it's one any one of the inputs

is high right so 1 0 it is one zero zero

it is 0 and 1 0 it is one right we will

take the third octet and verify it the

third octet we can see at least one of

the inputs is one right first four

places are zero in the IP address part

but fortunately we are having four ones

in the Subnet Mask Part the next two

bits are one here as well as here and

the next two bits are zero in the IP

address bar but one in the Subnet Mask

Part so at least one input is one in

this case

so we had just performed the bitwise or

operation now let's convert this octet

into decimal and when we convert this

octet into decimal we'll be getting 25

or

34.255.255 so this is the broadcast

address again I repeat when you are

intended to find the broadcast address

please ensure this step after converting

the subnet mask into binary do one's

complement and that's it guys before we

conclude let's see the homework question

the question is in a block of addresses

we know the IP address of one host is

182.44.82.16-26 what is the last address

that is the limited broadcast address in

this block so you are required to find

out the broadcast address

and that's it guys I hope you enjoyed

this lecture and thank you for watching

[Music]

[Applause]

[Music]