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!
If you like this video, don't forget to give it a thumbs up, leave a comment
and subscribe! The support from you guys really does help the channel grow
Other than that, I hope this helped and thank you for watching
you