Time
31 hours 29 minutes
Difficulty
Beginner
CEU/CPE
30

Video Description

OSI Model Layer 3 Network This lessons covers layer 3, the Network Layer of the OSI model. It is commonly referred to as the IP layer. This is where logical addresses are translates into physical and network routing, re-assembly and fragmentation are performed.

Video Transcription

00:04
our next layer is going to be our layer three known as our network layer. Now, our network layer is commonly referred to as our I p layer. Because this is this is where we're going to be using I p addresses.
00:16
Now, When we talked about our laywer, too, we mentioned Mac addresses. We talked about how Mac addresses are unique addresses for our individual network interface card and these unique addresses our point to point when we're sending on our data link. Later, when we're sitting on our laywer, too, we're sending data
00:35
point to point directly to a single Mac address
00:38
when we're sending through. Layer three were also sending to a single point. But Layer three is going to allow us to actually take that data and route it over different networks.
00:49
I p addresses are logical addresses. They're not physical addresses hard coded into our network interface cards. If we want to set a one computer a certain I P address one day and then change it to a completely different computer an hour later, we can do that. Their logical address is they're not hard coded, so
01:07
we're taking another step up even more away from our physical layer. So
01:15
at our layer three, we're going to translate our logical addresses. Our I P addresses to the physical to the physical addresses such a czar Mac addresses on our layer to our data link later, all of our computers with a network interface card have a Mac address, and they also have an I. P. Address. And you ask, Well, why do we need both?
01:34
Why can't we just use Mac addresses everywhere and just send data directly to a single computer in the world?
01:40
Well,
01:41
that would be That would be globally unique. Les i p version six i p addresses that are being developed, but we will talk about those a little bit later. But, uh, transferring data through Mac addresses over a global scale
02:00
is a little bit infeasible with the current. The way we currently have network set up. We need to be able to take a computer's Mac address, a sign, a particular i p address to that Mac address and then route data through Mac addresses over our networks. We'll do a diagram and a little bit, but let's go ahead and finish our points we have here
02:20
so
02:22
we talked about referring to our network. Layer is an I. P. Layer.
02:25
We talked about our network layer Well, we didn't talk about Arlette Network Layer being a functional means of transferring data through one or more networks.
02:34
If we have a Mac address and we're trying to transmit data to a computer on a different network, a computer in a different sub net, we can't transmit data to that computer by its Mac address. We need to use an I P address because between us and the computer on that other network,
02:51
we have to go through a router, and a router needs to have an I. P address
02:54
that it can use in order to transmit information. So this layer three is going to be where we're transmitting our data into different networks. We are going to be performing network routing functions. Layer three is going to do frag where we occur, encounter fragmentation
03:13
and reassembly of our different packets,
03:15
and we have our routers at Layer three. Our routers are going to be performing these network functions. They're going to be taking packets, looking at the I P addresses and sending them to their particular destinations or their particular up,
03:30
knowing where they came from. Rather, I promised you guys a little bit of a diagram to help explain this a little bit bit better. So let's take a look. Let's talk about the layers that we've hit so far now understand, in in this diagram, we're going to be omitting are layers 456 and seven just for simplicity's sake.
03:49
But in order to get a better understanding of these layers 12 and three, let's go ahead and let's go ahead and draw them out.
03:54
If we have computer A here and computer, A needs to send the data packet
03:59
while Computer A is going to take the data that it needs to send. It's going to take the the
04:04
packets that it needs to send, and it's going to
04:08
break them down into data that could be transported over physical means, so it's going to break them down into electrical impulses. These electrical impulses are then going to be then going to be sent out over our network interface card over a cable.
04:23
All of these parts of our network connectivity all of these cables, all of these bits and all of these electrical impulses are going to be layer one, the physical layer. If you hear someone referring thio an issue as a layer one issue,
04:41
that means that there's a problem somewhere between point A
04:45
and point B with the physical connections. So again, we mentioned earlier how the s I model can help us with troubleshooting. It can help us to identify where the issue is going on where the issue is in our transportation between one point and another point. So
05:01
we have our physical layer and we say, Oh, no, we have a layer one issue.
05:05
Well, because we know the S I model and we know that layer one is our physical layer. We know. Okay, a layaway. We're having a layer one issue that means there's something wrong with the physical connection. Maybe we had a table that was cut by accident. Maybe our network interface card burned out. Or maybe it was ripped out of the socket. Maybe our pins or bent
05:26
Those are all layer one
05:27
physical issues.
05:29
So
05:30
we have our electrical impulses
05:32
inside our computer to our network interface card to our cable.
05:38
Well, this network interface card has a unique address. We talked about the Mac address that sending Mac address is going to be a It's not. It may be written on our network interface card, but it's a It's a unique address that's assigned to that computer. A unique physical address
05:57
assigned
05:59
to that particular Mac
06:00
are to that particular network interface card. And that Mac address is going to be layer, too. So we have our Mac address. We have our data link layer, and if we were sending this data packet directly to computer, be
06:15
to its network interface card
06:17
directly to its Mac address, that would be the layer two point as well. Because it's the data link layer. It's that unique point to point connection.
06:27
But we can't do that.
06:29
This computer B is on a different network than us. Maybe it's in a different building. Maybe it's down the hall, but whatever the case is, it's on a different sub net than us.
06:39
So
06:40
because we need to connect to this over a different network,
06:43
we have a Layer three device in between us and this other other computer lead. Maybe we have a couple of these different devices, so on our side. We have a router
06:55
and then some cable connections through our building.
06:59
And then there's also a router on this other network.
07:03
So
07:04
for simplicity's sake, we're just gonna assign everything. One I p address routers will have to i p addresses in our actual networks because they'll have an I p address that faces us, and then they'll have an I P address that faces outward. And then the same with our other are other router. It would also have to i p addresses.
07:23
But just for simplicity's sake, we're gonna put our i p address just a single i p address
07:28
in order to identify our network.
07:30
So now we need to throw our layer three in here. We can't send. We can't use our data link layer and just send over layer two for Mac address to Mac address. So we need to put our third layer in. Here are layer three. Our network layer. We're gonna have i p addresses on computer A. This is gonna be 1 92 dot
07:49
1 68.1 dot 15.
07:55
Our routers going to be 1 92.1 68.1 dot one
08:01
and That's our network. A router. Our network be router is going to have the i P. Address of 10.0 dot 0.1. And our computer B is going to have the i P. Address of
08:16
10.0 dot 0.17.
08:22
These I P addresses are in different networks, so our computer needs to go through the router.
08:26
So
08:28
we have our date. We have our data that we took and we put made into bits.
08:31
We then made the took those bits, and we made them into frames on our laywer too.
08:37
S So what do we have now? We need to package that data up so we can send it across. Our network are layer three.
08:43
We're gonna have packets.
08:46
So we've now taking that data. We've taken those frames we've put, we've started to network them. We've given an I p addresses and we now have packets.
08:54
We're going to say, Take those packets and we're going to send them to our router,
09:01
which which is a layer three device. A router is a layer three device,
09:05
and our router is going to take that data and it's going to route it to our separate network here,
09:13
and then it's going to allow it to connect to our computer
09:16
once that data gets to the point where it's now sending directly to the Mac address, and it's now going directly to that to that single computer. Now we're back at our layer to again because we're sending directly to to the Mac address. And then once that data is back in our network interface card and being transfer
09:35
transmitted back to electrical signals,
09:39
we're back in a layer one again. We're back in our physical layer. So
09:43
at any given point in our connection between computer A and Computer B, we have all three of these layers sort of performing at the same time.
09:52
Our electrical signals don't stop at layer at Computer A. When they leave our computer. We have electrical signals going on between our two routers, so we still have layer one connective ity going on.
10:03
We when we are transmitting data and we're using when we're transmitting between our router and our computer B, we have layer two. We have data links going on,
10:16
and when we are transferring between our router be are rather too, and our computer be. We still have those physical layers going on. So all three layers are working together on their building, on top of each other in order to provide connective ity. When we are discussing and we're trying to troubleshoot issues and we say that
10:35
we're having layer one connective ity we're having layer one issues
10:39
between the two routers. Maybe a cable got cut on. So we consider that a layer one issue because everything is correct with our data link. And everything's correct with our I p addresses in our network layer. But the issue is at our layer one issues with the physical connection.
10:56
So
10:56
this is our This is the one of our ways that we can understand how Layer three works again. We are omitting a lot of steps were emitting a lot of details with this connection that's going on here. But
11:09
the big things to remember with our layer three, our network layer is that this is going to be also referred to as our I p layer.
11:18
This is where we're going to be transmitting data to one or multiple to more than one networks. And this is also going to be where our routers are functioning at our network layer

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