Introduction to networking

We live in an incredible world today where we could use our smartphones and get all kinds of information, or we can sit at our desktops and play incredible games with other people in real time. It is a great, great time to be a tech. However, the CompTIA A+ really wants you to understand networking in a deep and profound way. So if you really want to understand networking well enough to be able to pass the A+ and to succeed as a technician out there, we've got to bring it down a little bit. Forget the smart phones, forget the fancy tablets, forget Google. Let's take it back down to a simpler world, a time before the Internet, a time when networking was really just for a few computers, maybe five computers, maybe 15, maybe 20 computers that work together in the same office that we're all hooked together. And the only thing they shared back in the old days was they probably share a printer and they probably share each other's folders so that we could access each other's Microsoft Word documents. So we're going back to a very, very simple time, very basic networking and what we call a local area network or LAN. So let's talk about that for a minute. So imagine I've got a nice little office here and I've got some people with some computers and they're working away. And maybe there's somebody with a laptop over here and here's a printer. And what we would do back in the old days and still do today is we would run wires not between the computers, but to a central little box that at least for the moment I'm going to call a hub. So everybody is physically connected from this central point called, again Momentarily, we're going to call it a hub. Now, in today's society, it still works that way. In a wireless world, for example, we would have something called a Wireless Access Point, and everybody's talking on the same frequency to that particular Wireless Access Point. Well, that sounds okay, but right off the top, I see two big problems. Problem number one, how do we keep any one person from hogging up the network? And problem number two, how do we know how to send data to this computer and not that computer? Let's take a look. So imagine a situation where I've got Shannon and Dana who are all plugged together on this one local area network. Now, Dana wants to access Shannon's Microsoft Word document. Now, if she were to simply start grabbing that, anybody else who wanted to talk, let's say it's a huge document. He kind of hogs up everything and that could be a real problem. So to keep anybody from hogging up the entire network, a bunch of folks got together back really in the late 1970s and developed a type of networking called Ethernet. Now, it may be old, but it is still the most popular type of networking that we use today. Ethernet defines what kind of cabling we use, what kind of these little hubs. It defines speeds. It defines all kinds of stuff. But it also defines something really important. And it says you can only make your data in discrete chunks of 1500 bytes. So if you want to send data, for example, if you want to send a Microsoft Word document and it's 100 megabytes big, that'd be a big word document. It has to be broken up into zillions of these little 1500 byte chunks called a frame. Now, don't worry. We'll see that the operating systems have the smarts to take the word document apart and then put it back together on the other end. But for right now, a frame is only going to be 1500 bytes tops. Well, that takes care of one problem, but it doesn't take care of another. So here's port Dana over here, and she wants to go talk to the Shannon computer because she wants to get a hold of this Microsoft Word document. But there's lots of other computers on this network. We have to come up with some way to uniquely identify each computer on the network so that we know how to talk to these guys and not to the others. So what I've got set up in front of me is a very, very simple network. So here's one computer. Now, it used to be we had network cards, you snap in, but they're all pretty much built into the motherboards today. So on this motherboard right here is a Ethernet connection. And as we go over to this other one, he's got an Ethernet connection as well. And they all come together in this central box, which I'm going to temporarily call a hub. In fact, there's even another computer I don't care about, he's somewhere else. So in this particular situation, I've got three computers. We uniquely identify every system on the local area network through something called a Media Access Control or MAC address. A MAC address is a 48 bit address, which is always manifested as 12 hexadecimal characters. So let's put up a MAC address right here. So this is example of what a MAC address might look like. So every network card in the universe gets a unique MAC address. So if it's got 12 hexadecimal characters, the first six characters are what we call the OEM ID. So if I'm going to start making network cards, I am issued those first six characters from the issuing body of the Internet, and then I can spin up all the other ones as much as I want. So these two computers in front of me have MAC on them. So what I'm going to do is, his MAC address is this and this one's Mac address looks like that. Would you like to see the MAC addresses on your computers? It's easy. If you're on a Windows system, just open up a command prompt and type in the command ipconfig /all, A-L-L. If you type it, you're going to see something that looks like this. There's a lot in there. But there's one particular line I want you to concentrate on. You see where it says physical address? That's the actual MAC address for the network card in your computer. This also works with Mac as well as Linux systems, except you use the command if config, or you could just use IF and you can get basically similar results. All right. So we now have MAC addresses that are assigned to every network card out there. 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 we send out a frame, instead of just the data at the beginning, we're going to put the destination MAC address and then the source MAC address. So actually, I've got some MAC addresses in here already. So this will get it to the correct computer. And as a courtesy, we always put the source MAC address in case they want to talk back to us, they know our MAC address already. 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 frame check sequence or FCS. The frame check sequence is nothing more than a checker, so that when this data gets over to its destination, they can compare this value to the data and it gives them a pretty good idea as to whether the data came in in good order. So what you're looking at here is the basics of what we call an Ethernet frame. These frames were invented almost 40 years ago and we still use them on the highest speed networks out there today. What you may not be noticing is a term that people love to use a lot called IP address. IP addresses are important, but in a small local area network like this, they don't really do much. In order to appreciate IP addresses, we need to start making our networks bigger through something called a wide area network.