Last year, we talked about the network ports, which need to be aware of that reporting protocols and
that we just want to take in to the network layer network layer in this layer.
We are concerned with really one thing, and this is the thing that most people aren't aware of is IP
addresses.
But you have a source, IP address, IP, all that data, all that information was here.
And this is referred to as a hockey player for TCP.
First you out of the segment.
But when it gets down to a three, the data, the protocol, you, to be more precise, becomes a packet
and then it layer to the protocol data unit or the packet becomes a frame.
Right.
And the frame really just looks like this.
Conceptually speaking, we can do.
It's going to get us out and said here.
Data link where OK, so I have a data link later, we have friends, but we really have Mac addresses.
So let's put frame here and you have a source Mac address.
You have Adeste Mac address.
This is what switches care about, right?
Switches forward frames in the Mac addresses.
Really are concerned with your local network packets are concerned with the Internet.
So when you think about an IP address, think about end in connectivity.
Right.
Point A to point B when you think about a Mac address, think about the immediate next top.
Let's call this like eight point one, OK?
There's all these other devices like routers and but yet there's a bunch of routers between, you know,
my computer and the ultimate computer that I want to get to.
And so the frame is going to hop between these devices to up three, so on and so forth, until it gets
to its final destination.
So when you look at Mac addresses.
The definition of Mac is not going to be this far in whatsoever, but down here, it's actually going
to be your local router or your gateway is going to be the Mac address of interface on your default
gateway.
Right.
And then the frame is going to be forwarded to the next top, which will most likely be another device,
a router that is between you and the ultimate website.
So you can actually see this kind of an action if you weren't.
So let me show you what I'm talking about here.
So if I go into this computer.
Simbi.
I went ping on example about.
Let's say up to IPV six a.m., that's kind of annoying.
I think we need to disable that, so what we're going to do TechNet, S.H., I'm sorry, inseparate
KPL.
And let's disable IPV six.
If we can use my network adapter.
Properties.
IPV six.
OK, close.
Close, let's open up an elevated command prompt.
And as administrator.
We'll say half example com.
This is my general address.
This is layer three network address, and by the way, example, dot com is a real website example,
dot com.
So this is a real page on the Internet, as you can see, it's taking forever a prisoner that I can
respond, but this is another I.P. address on my local network.
So megadoses are being Utøya.
You can actually see them.
I could reference and show you this.
That are being resolved by my computer.
Ah, ah, ah ah, so ah, address, resolution, protocol.
Show me everything and the IP config.
You can see 190, 116 zero one, my default gateway, one of seven is my actual address that.
Zero one is by default gateway, and it's the macros that, if it was learned dynamically, right,
is a few of the devices on here, because I've got a few other devices listening in my lab.
But the point is now this is the definition math, right?
For that first frame we fired up Wireshark, you would actually see this Wireshark.
Called this out, you know why that's taking so long?
Here we go.
Making some progress.
Let's start this over so control see, I'm just going to clear this out.
Let's get Wireshark going to capture on our Ethernet adapter.
People say path paying, for example.
Com.
Should be able to filter down by ICMP just to look at the pings.
And you can actually see the entire, you know, what's stock here, this is the application layer protocol.
In this case, there's an application layer protocol because I sent it directly from the command prompt.
So we're starting here at layer four.
This is TCP.
And you can actually see the sequence numbers over here, by the way, then we have layer three where
you have now a packet.
So the segment moves down, it becomes a packet.
Here's the source and destination IP address.
And then the packet becomes a frame and you have the source destination Mac addresses if you look at
AAFP or type AAFP.
You'll see a list of all the devices on my network.
I've got a lot of activity, but you can see my computer doing some work here.
So if I go into the command, prompt the IP address again.
You see him zero point one of seven, right?
Here you can see my computer and seeing who is one only two one six zero one one seven.
That's me right to my router saying, who is this guy trying to ping me?
And remember, that's the first hop when we went to the path ping.
Right.
It's like Pathing Felde example.
It's not going as well as I wanted to, but the first hop is going to be the the router, OK, my my
personal router or my home network.
And it's basically saying, you know, the router gets that frame.
It's like, well, you know, who is this one?
And two one six eight zero one seven guy.
Tell me the router and then my computer responds with my address.
And how do I know with my Mac address.
This is 030.
Well I can tell you right now I hear this f 030 is my back address because if you go to the command
prompt IP config but you need to run.
All.
There it is, is my Mac address of 030.
If there were 30, right, and so now my Mac address has been given to the router and now the router
has a way of moving that frame to the next hop, which is going to be another router within my ISP network.
They're going to get it.
And, you know, they're going to say, well, who you know, who has this particular IP address?
It's going to go through the entire resolution process all over again until it finally ends up at the
example dot com.
Domain.
OK, so the main thing I really wanted you to learn here is that the data moves down a protocol stack,
OK, transport network and doing OK.
Your segment, as we said before, packett.
Fred, and then it's going to keep moving.
From routed around her.
And between these routers, it's using.
Mac addresses the Mac addresses a constantly changing as the frame moves between routers, but the IP
address always stays the same.
The source and destination IP, the source does always stay the same.
But the the source and destination Mac address is always changing.
Right?
Because when you hear the source, Mac, it's going to be the source, the Mac address on my computer
when the frame moves to the router.
By the way, the destination Mac will be this rather my default gateway, but not one that gets to the
router.
The source, Mac, is not going to be the routers Mac address on this interface right here.
The destination Mac is going to be this far end interface and then this matter is going to get it.
And remember, the IP address stays the same, the source IP stays the same and the destination IP stays
the same.
Whether this router gets it basically encapsulates the frame and it looks at the source, Mac, and
it says, OK, the source Mac, is this guy over here, destination Mac is me.
Cool when it decathletes the candidates at the packet, but it sees the IP address is not its latest
address.
Instead, it's the example dot com IP address.
So now this router knows it needs to move that frame to the next hub that will play a role in getting
that frame to its ultimate destination.
So the traffic gets it right.
It looks at the source Mac address, source Mac address is coming from this guy destination Mac.
If this router sort of said, cool, let me open it up, let me look at the network layer.
Network layer has a source IP of this address, which is fine definition.
Is not this routers destination, it's not this routers layer three network interface card.
So it moves the frame again to the next hub.
And this happens until it gets to this example dot com server and when it gets there.
This is the server that's running this whole thing is apple dotcom, let's say that's what this is.
This server is going to get it and the destination, Mac is going to be this particular router destination.
IP is going to beat this routers layer three IP address.
Now, it knows that it can move that packet, which came in as a frame up to layer four, move it up
to layer four, which is where the application was, which is listening.
Aiport 80.
Right.
It could be a patch.
You could be is it processes that data and sends back the response, which would be the actual page.
Right.
So we can look at that.
It's clear the screen in the fast.
You can see some of this happening if you look at chrome tools, dev tools.
So we go here, we're going to go to dev tools, more tools, developer tools.
It's a good network.
Flip this over like this.
So we're going to refresh this.
Shift a five, let's safety a hard refresh, there we go.
You can see the data that was requested, so there's the IP address, Port 80 CE in the response.
Let's see, what do we get back?
Response setters see the source.
So here's the response headers in the contently with six forty eight, I mean, to set back the page
that was six hundred forty eight bytes, which is exactly what you're seeing here.
OK, and also sent back as Babycham, which is what you're seeing up here in Chrome.
Of course, it was found that found so it tried to request it.
It was a four or four, so it didn't actually get that back.
That's basically how that works.
You know, it's not really that complicated to remember the lessons for the land and or the internal
that the communication, you know, within a subnet and then the IP addresses are encrypted.
Right.
So I hope that makes sense.
And I will see you in the next one.