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We live in an incredible world today where we could use our smartphones and get all kinds of information
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are we considered our desktops and play incredible games with other people in real time.
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It is a great great time to be a tech.
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However they come to you a plus really wants you to understand networking in a deep and profound way.
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So if you really want to understand networking well enough to be able to pass the A plus and to succeed
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as a technician out there we've got to bring it down a little bit forget the smartphones.
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Forget the fancy tablets.
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Forget Google.
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Let's take it down to a simpler world a time before the internet a time when networking was really just
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for a few computers maybe five computers maybe 15 maybe 20 computers that work together in the same
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office that we're all hooked together and the only thing they shared back in the old days was they probably
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share a printer and they probably share each other's folders so that we could access each other's Microsoft
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Word documents.
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So we're going back to a very very simple time very basic networking and what we call a local area network
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or LAN.
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So let's talk about that for a minute.
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So imagine I've got a nice little office here and I've got some people with some computers and they're
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working away and maybe there's somebody with a laptop over here and here's a printer and what we would
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do back in the old days and still do today is we would run wires not between the computers but to a
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central little box that at least for the moment I'm going to call a hub.
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So everybody is physically connected from this central point called again.
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Momentarily we're going to call it a hub.
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Now in today's society it still works that way in a wireless world for example we would have something
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called a wireless access point and everybody's talking on the same frequency to that particular wireless
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access point.
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Well that sounds OK but right off the top I see two big problems.
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Problem number one how do we keep any one person from hogging up the network and problem number two.
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How do we know how to send data to this computer and not that computer.
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Let's take a look.
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So imagine a situation where I've got Shannon data who are all plugged together on this one local area
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network.
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Now Dana wants to access Shannon's Microsoft Word document.
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Now if she were to simply start grabbing that anybody else who wanted to talk would say it's a huge
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document.
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He kind of hogs up everything and that could be a real problem.
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So to keep anybody from hogging up the entire network a bunch of folks got together back really in the
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late 1970s and developed a type of networking called Ethernet.
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Now it may be old but it is still the most popular type of networking that we use today Ethernet defines
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what kind of cabling we use what kind of these little hubs.
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It defines speeds and defines all kinds of stuff but it also to find something really important and
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it says you can only make your data in discrete chunks of fifteen hundred bytes.
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So if you want to send data.
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For example if you want to send a Microsoft Word document and it's 100 megabytes big there'd be a big
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word document.
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It has to be broken up into zillions of these little fifteen hundred by chunks called a frame.
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Now don't worry we'll see that the operating systems have the smarts to take the word document apart
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and then put it back together on the other end.
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But for right now a frame is only going to be fifteen hundred bytes tops.
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Well that takes care of one problem but it doesn't take care of another.
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So here's poor data over here and she wants to go talk to the Shannon computer because she wants to
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get a hold of this Microsoft Word document.
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But there's lots of other computers on this network.
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We have to come up with some way to uniquely identify each computer on the network so that we know how
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to talk to these guys and not to the others.
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So what I've got set up in front of me is a very very simple network.
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So here's one computer now it used to be we had network cards you snap in but they're all pretty much
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built into the motherboards today.
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So on this motherboard right here is a Ethernet connection.
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And as we go over to this other one he's got an ethernet connection as well and they all come together
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in this central box which I'm going to temporarily call a hub.
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In fact there's even another computer I don't care about.
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He's somewhere else.
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So in this particular situation I've got three computers we uniquely identify every system on the local
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area network through something called a media access control or MAC address a MAC address is a 48 bit
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address which is always manifested as 12 hexadecimal characters.
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So let's put up a MAC address right here.
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So this is example of what a MAC address might look like.
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So every network card in the universe gets a unique MAC address.
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So if it's got 12 hexadecimal characters the first six characters are what we call the OEM I.D..
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So if I'm going to start making network cards I am issued those first six characters from the issuing
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body of the Internet and then I could spin up all the other ones as much as I want.
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So these two computers in front of me have Mac on them.
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So what I'm gonna do is his mac address is this.
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And this one's MAC address looks like that.
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Would you like to see the MAC addresses on your computers.
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It's easy.
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If you go on a Windows system just open up a command prompt and type in the command I.P. config space
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slash all hll if you type it you're going to see something that looks like this.
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There's a lot in there but there's one particular line I want you to concentrate on.
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You see it says physical address.
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That's the actual MAC address for the network card and your computer.
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This also works with Mac as well as Linux systems except you use the command I f config or you could
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just use i f and you can get basically similar results.
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All right.
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So we now have mac addresses that are assigned to every network card out there.
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So what I'm going to do now is I'm going to add to this frame and what we're going to do every time
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we send out a frame
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instead of just the data at the beginning we're going to put the destination MAC address and then the
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source back address.
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So actually I've got some mac addresses in here already.
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So this will get it to the correct computer.
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And as a courtesy we always put the source MAC address in case they want to talk back to us.
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They know our mac address already.
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Now as you take a look at this there's only one other thing I want to add and that is what we call a
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frame check sequence or FCX the frame check sequence is nothing more than a checker so that when this
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data gets over to its destination they can compare this value to the data and it gives them a pretty
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good idea as to whether the data came in in good order.
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So what you're looking at here is the basics of what we call an Ethernet frame.
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These frames were invented almost 40 years ago and we still use them on the highest speed networks out
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there today.
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What you may not be noticing is a term that people love to use a lot called IP address.
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IP addresses are important but in a small local area network like this they don't really do much in
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order to appreciate IP addresses.
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We need to start making our networks bigger through something called a wide area network.
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