next, we're gonna move on
to the next layer in our side. Leered model stock, which is your network, lier or Lear three. The network clear controls communication
between broadcast domains. So if you want to go from one broadcast domain to another broadcast domain, you need layer three,
specifically, the device that works at the network clear.
So to draw out an example, let's say you have a switch here
with two hosts or to PC sitting on it,
and you know that a switch is one broadcast domain by default. So let's say we only have the land one here. This isn't the line one.
This is villain one,
and then you have another switch and this is in this. PC
three is in Villain 50 for example, on P C four is also in veal and 50.
So if you want PC one, which is in villain, want to communicate with PC Tree, which is in villain 50. You need to use layer three or more specifically, you need a router. You cannot connect these two switches back to back with each other because
BC ones just simply not gonna talk to PC three
because doulas are two separate broadcast to means now granted villains earlier to broadcast domains. And in a little bit we're gonna cover Lear three broadcast domains. But the concept remains the same. To go from one broadcast in this case, Vienna one to another broadcast domains,
which is in this case, villain 50. You need the process of routing, which is a layer three function, and the device that provides the process of routing is called a router. So the device that works at Lear three
and the function of layer tree is to send data between broadcast domains.
Now, the protocol data unit at layer to was called a frame.
The protocol data unit at Layer three is called a packet.
Before I draw the packet structure
just like at layer to you needed some sort of add racing scream.
So just like it later to you needed some sort of address ing scheme to send
frames between devices. So you needed a source Mac address and a destination Mac address. So the address in scheme at Lear to was Mac addresses
at Lear three. The addresses that are used are called I P Addresses.
So let's begin with I p addresses and I. P Address is 32 bits in length, and it's written in four fields off eight bits, each separated by a dot
This is called the dotted decimal
format. So four fields of a bits each.
Let's find out what it looks like. So ex dot x dot exe
dot x equals 32 bits
Exes. A number X is a variable. I put X Instead of putting a number, we'll discuss what goes in the place off exit in a second.
Now, each one of these fields is eight bits,
plus eight plus eight plus eight times four equals 32.
So let's take this first field and expanded out into its constituent bits.
2345678 So I'm basically taking this first field,
also known as an octet. Not really
hard to think about how they came by that Eight bits octet, octopus.
And once again, we're gonna number these bits
which, with specific values
You double it, you go to to you double it four. Double it 8 16
32 64 on 1 28 So 1248 16 32 64 1 28
Once again, I'm drawing out this first octet or this force field.
If I turn all these bits
off and I put zeros on top,
then I get a value totaling zero.
However, if I turn all these bits on
which is a value one,
then I need to add all these numbers up to get what value
So 1 28 plus 64 is 1 92 plus 32 is to 24 plus 16 is to 40 plus eight is to 48
plus fours. 2 52 plus two is to 54 plus one is 2 55 each. One of these values, each one of these field or octet can very arranged between zero and +255 the maximum value being +255 the minimum value being zero.
So an I p address, which looks something
Tenn 0.0 dot 1 28 dot
depending on which bits are turned on
and which bits are turned off within each successive field or each successive octet.
So, for example, over here.
Only the 1 28 value is turned on and the rest of them are off
on the first octet. The eight bit value and the two bit value are turned on
and the rest of them are turned off because a plus two is
so back in the day when the Internet was young and I p address ng was brand new
I p address ng was broken down into class is called class ful I p addressing
And there are certain rules that must be followed with costal I p address ng Nowadays
I p addresses are not broken down
class Feli. They're broken down past Leslie.
However, to understand class less I p address ing. You must have somewhat of a grass or a firm grasp Off class full I p address ing where I p addresses are broken down into classes.
So the first class we have this class for classy addresses. The next field I'm supposed to fill out is the value of the first.
So, for example, in the ex dot x dot x dot
ex example, this is your first octet. This is your second octet. This is your third octet. and this is your fourth doctor, So I'm only going to put the value of the first octet
for classy addresses. The value of the first octet has to be a number between one and 1 26
If it's not, then it's not a classy address. So in this case, this number has to be a number between one and 1 26
Now there's something called the sub Net mask.
I'm going to explain what a sub net mask is in a little bit right now. Just take it for face value.
The subnet mask for a classy address,
000 So the first octet, as you saw, is all ones.
The 3rd 4th and fifth octet are set to zero.
Now, what is this cider notation or stress? Less inter dumaine routing notation.
This is basically a way for us to be a little lazy
instead of writing to 55000
If I were to ask you how many bits in the sub net mask are on at this point,
there are eight bits on
since all the bits in the first octet, which is eight bits
are on. You get the value to 55
so I can simply denote this whole thing as slash eight
h being the number of bits that are on in the sub net mask.
As an example for a classy address,
I can save 10.10 abduction
that 10 slash eight,
which would be the same as seeing 10 dot Tenn dot Tenn 10.0.0.10 to 55000
The next class we have is Class B
for Class B. The value of the first octet must be a number between 1 28 and 1 91 I haven't forgotten the number 1 27 I'll get get to it in a minute.
So for Class B, the value of the first octet has to be a number between 1 28 and 1 91
The sub net mask is 255.2550 dot zero. So now
would would the classless inter domain routing notation be or decider notation be
the first octane is all ones, which is eight bits.
The second octave is also all ones, which is another eight bits so eight plus eight is 16.
The third and fourth op ed are off. You get slash 16
off a Class B address would be
1 51 No. One, not 45 not 45
Next, you have Class C for class. See the value of the first octet again. Keep in mind this is just the value off the first number, the first field for the first octet.
So the value of the first octet has to be a number between 1 92 and 2 23 and the sub net mask is through 55.255 dot 255.0.
What would decider notation being? Well, The first octet is all on,
which is eight bits. So is the second doctor, which is again eight bits. So is the third doctor, which is again eight bits eight times three is 24 24 total on bits in the sub net. Mask. So I can say slash 20
Then there's also a Class D Class D. Addresses range between 2 24 and 2 39 class. The addresses do not have a sub net mask and they are used in multi casting.
Now we all know what a unique Castor's. A unique *** is 1 to 1 transmission.
We know what a broadcast this.
It's like junk mail, one to everybody transmission.
You're gonna get it, whether you want to or not.
Ah, monthly cast is like a magazine subscription. It is a one too many transmission. But the hosts
have to be subscribed to the feed.
ah, monthly cast is a magazine
subscription. Like unless you subscribed to it, you're not going to receive it.
Ah, broadcast is like junk mail. You're gonna receive it whether you want to or not. Then there is a Class E. I believe it goes from to 40 all the way to 255 And this is experimental. So experimental and unused.
You noticed that I left the number 1 27 out.
1 27 is not in this range. The whole range 1 27.0 dot 0.0
is reserved for testing.
is called the local loop back
if you can. Ping Ping is a testing utility utility. If you can reach this address,
okay, or if you can ping this address now, we'll go into more detail what Ping is and what protocol that uses later on. But if you can, for now, if you can reach this address
or test for this address using a command a utility called Ping,
then that means that the TCP I P parochial stack was properly installed on your machine.
If you cannot bring this address,
take your PC back to Best Buy.