IP Addresses Explained | Cisco CCNA 200-301 - YouTube

So we're going down the tcp/ip model as if we were sending data, so top to bottom

In the last videos we saw how data can be sent using TCP and UDP. We also saw

how data gets to a particular application using port numbers. Now we're

moving down to the network layer to see how that data actually gets to the

destination. this layer is responsible for IP addresses

So what is an IP address? An IP address is a unique identifier

assigned to each device connected to a computer network

The most common analogy for an IP address is the postal service. For the

postal service to work every house needs to have its own unique address

and if you need to send a letter, not that anyone sends letters anymore

you need to write the destination address on the envelope. That way when

you send the letter the postman knows exactly where to deliver it

now the address must be unique. Otherwise your post could end up going to somebody

else or you could start receiving somebody else's post and that can

sometimes not go so well. Computers work in the same way. Each computer in a

network needs to have a unique address called an IP address and when sending

data to a computer, just like letters we need to add the destination address. We

also need to include a return address so they know where to reply

So let's look at an IP address. This is an ipv4 address which at the time of

making this video and probably for a long time after is the most common

although we are slowly moving over to the new IP version 6 that will be

covered in another video. So an ipv4 address is 32 bits in length

which means it contains 32 binary digits. We'll look at this more when we go over

subnetting. It contains four sections which are called

octets. These octets are separated by dots or

periods. Each octet in theory

can contain any number between 0 and 255 Why 255? well our

32 bit number is separated into four lots of eight, and 255 is the largest number

that can be made from eight bits

Now the address itself is separated into two parts, the first part represents the

network and the second part represents the host. To know which part of the IP

address represents the network, we used to rely on the first few binary bits but

since the early 90s we have something called a subnet mask. A subnet mask is

always paired with an IP address and is used to identify the network section and

the host section of the address. In its simplest form whenever you see

255 this is the network part of the address whenever you see a 0 this is the

host part of the address. It can get a bit more complicated than that

but we'll look at that later on down the line. When learning about networks and

hosts and what they mean, it's good to think of it like your address

You shared the same street name as your neighbors but it's the house number that

makes your address unique. On the other hand, you can also have

multiple streets with the same house number. And it's the same with computer

networks. Instead of street addresses you have

network numbers and instead of house numbers you have host numbers. Here we

have two networks 192.168.5.0 and 192.168.10.0 both with a subnet of

255.255.255.0. When talking about networks as a whole, you often just use 0 for the

host section. Inside our networks we have our hosts .1 .2 and .3

It's common in a network diagram to just show the host section of the address if you

already know the network section. In fact these IP addresses would be 192.168.5.1

192.168.5.2 and so on, and so on

So with all of that in mind if we have some data to send to 192.168.5.3

with a subnet mask of 255.255.255.0

where would we send it? Well if we look at the subnet mask we

can see that the network is 192.168.5 So we know that three is our host number so we send

it over to the host in the network on the left

Hopefully that all makes sense so far. Back in the early days of IP it was

decided to split all of the available dresses into groups and these groups

were called classes. The idea was to make address allocation scalable. The main

ones being Class A, Class B and Class C. There is also Class D for something

called multicast addresses and Class E which is reserved for experimental use

We're going to focus on the first three. Each class has a range of IP addresses

Class A addresses are between 1.0.0.0 to 126.255.255.255 with a

the subnet mask of 255.0.0.0 Class B addresses are between 128.0.0.0 to

191.255.255.255 where the subnet mask of 255.255.0.0

and Class C addresses are between 192.0.0.0 to 223.255.255.255

with a subnet mask of 255.255.255.0. Phew! After that never want

to say 255 again! So this was all to control the number of hosts available on

each network. Class A has three octets available for host allocation this means

we can have 16,777,214 hosts for a single class a network. Massive, massive networks!

Class B has two available octets for host allocation so we can only have 65,534

hosts to a single Class B network

Still a very, very big number! Class C only has one available octet for

host allocation. So this means we can get 254 hosts per single Class C Network

So you need to be able to look at an IP address and know which class it belongs to

The easiest ways to do this is to memorize the first octet. If an IP starts

with the number 10 straightaway you know it's a class A network. If it starts with

192 you know its Class C and so on and so on

but there's a problem. The problem is no one could have predicted the massive

explosion of computers and the Internet. In fact there are no more unallocated IP

version 4 addresses left. This is why the new IP version 6 has been designed

It will give us more than enough IP addresses for absolutely everyone

But fear not! there is a solution to help prolong the life of IP version 4

The solution is to carve out small sections from all three classes and call them

private IP addresses. All other addresses are known as public addresses. They still

use the same subnet mask for that class and they can still have the same number

of hosts. The difference is where public IP addresses need to be unique, private

addresses can be used over and over and over again, thus saving millions or

billions of public IP addresses. This is how it works. Let's say this is

your house. You have a PC a phone and a printer. You can choose any private IP

range that you want to use. In this case we will choose Class C

192.168.1.0 and we'll assign our IP addresses. Remember this is a Class C

Network and the default subnet mask is 255.255.255.0 meaning 192.168.1.0

is our network address and the last number is our host address

So all of our devices can talk to each other

without any problems at all. The beauty of private IP addresses is

that they can be used by anyone. For example your neighbors might also be

using the same IP addresses as you are. And that's fine, private IP addresses

only need to be unique within your own network. There is a catch though, private

IP addresses cannot be used over the Internet

Otherwise we would have duplicate IP addresses everywhere and data would

never end up getting to the correct places. For that reason only public IP

addresses can be used over the Internet. These must be unique. When you sign up

with your internet service provider, they will issue you with a public IP address

that you can use over the Internet. Usually, they give you just one address

not a block off 65,000 or 254...1! This helps prolong the life of ipv4

because instead of using an IP address for every one of our six devices we are

only using two public addresses. The way our devices will communicate to

the internet through their public IP is by using something called

Network Address Translation, which again we will cover in a separate video. Before we

finish this video, I will show you how to check your own IP addresses at home on

On Windows you simply open a command prompt or PowerShell

type ipconfig to see your interface settings

find your interface, you might have more than one if you have wireless, and you'll

be able to see your IP address and subnet mask

for Linux or Apple computers open a terminal

and type ifconfig and you should see the same information

to view your public IP address simply open a browser

go to google and type in "what is my IP" and it will show you your public IP address

So we still have a lot to go over when

we're talking about IP addresses. We need to cover binary and subnetting but I

think that's enough for one video. This video is part of our full CCNA course

which can be found in the description. So please feel free to go and check that out!

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Other than that, I hope this helped and thank you for watching

you