From the course: CompTIA A+ Core 1 (220-1201) Cert Prep

WANs and routers

From the course: CompTIA A+ Core 1 (220-1201) Cert Prep

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WANs and routers

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- What I've got in front of me is what we call a 24-port switch. Now, these switches are based on a standard called ethernet, which we've been using for ages and ages. Ethernet is absolutely amazing. It works incredibly well. Our ethernet frame is sending data back and forth in our LAN using the MAC addresses, everything's fantastic, as long as you keep it relatively small. So if I'm using this switch, the most computers I could put on one local area network would be 24. Well, there actually is a way to interconnect switches, but the ethernet standard itself says you will never ever put more than 1,024 computers on a single switch or a bunch of daisy chained switches. There's reasons for that. First of all, when you're looking at a local area network, there's a lot of stuff going on. Let me show you what I mean. On this particular local area network, I've got two computers, A and B. Now these two computers are hooked to three different switches. Now, because these switches are daisy chained together, they pretty much act like one single switch. Now this works beautifully well until we start adding lots more computers. As we add more and more computers into this, and I'm saying way before we get to that 1,024 computer limit, even with the switches making point-to-point connections, the system becomes horribly overloaded. Heaven forbid you would actually want to connect more than even 1,024. What if you wanted to connect potentially millions of computers together, both wired and wirelessly, and make this thing called the internet? Well, the problem is, is ethernet is not going to hack it. The concept of a LAN works fantastic for up to, according to ethernet standards, up to 1,024. But in reality, 30 to 40 computers is pretty much the standard maximum size for a local area network. We have to come up with some totally different system here. We have to use a system that bases addressing not on the MAC address, but on some other type of address that allows us to, instead of having this one massive LAN, let's make hundreds, thousands, potentially millions of little LANs and then interconnect them together through something called a wide area network. So, let's talk about this a little bit. So here's a four computer local area network connected to one switch. I don't care that it's four. It could be 20 computers for all I care about. In fact, instead of drawing all this out, would it be okay if I just drew a circle? And this circle identifies a local area network. So we're going to call it LAN 1. If we have lots of LANs and we want these guys to be able to intercommunicate, we've got to come up with an addressing system that allows one computer over here in LAN 1 to be able to connect to this local area network over here in LAN 4. So we need some kind of traffic cop, some kind of magic box in the middle that will be connected to our switches, but on the same token, it will be able to go, ah, this piece of data needs to go to LAN 3, or this piece of data needs to go to LAN 2. So, we need some kind of magic box. I've got one of these magic boxes right here in front of me. This magic box here in my right hand is called a router. Now, just for comparison's sake, here in my left hand, I have just a regular good old five-port switch. Nothing special here, but by looking at them, they seem to be the same, but they're extremely different. Routers are sensitive to different local area networks and could differentiate not between just individual computers, but different LANs. The trick here is that the MAC address allows us to get information to different computers within a LAN, but I need a different numbering system, something else that allows me to identify local area networks, and that's where we get into what we call logical addressing. So if a MAC address is a physical address, because it's burned in at the factory, a logical address is something, when I buy a computer and I put it in my LAN, I have to type something in to go, ah, this computer is a member of my local area network. And if somebody else goes to the same store and goes to a different LAN, they can type in something to identify their local area network. So, there's a value that we type in that identifies us as a particular LAN. Let's talk about how we'd go about identifying it. Keep in mind this is a software function that we can enter. So, we can type in anything as long as everybody all across the Earth agrees on it. Let's brainstorm. So just for fun, I'm going to call this LAN A, this one, LAN B, this one, LAN C, and this one LAN D. The cool part is that we would then go into the router, let's zoom in on that router a little bit, and just as a switch, will memorize the MAC address for individual computers, this router will know this logical address and we actually will have to punch this into the router. There's a way to configure this, and we're going to tell the router, all the computers plugged in here are going to be part of LAN B. All the computers plugged in here are part of LAN A. All the computers here are LAN D. All these go into LAN C. So, let's draw a local area network that most of us know and love. Here's the local area network in our house. So, there's usually some box. Now, I know a lot of people call this a router, but for right now, let's pretend like it's a switch. So, I've got a laptop over here and maybe this switch even does wireless stuff. So, here's a smartphone over here. And here's your Google Home hockey puck. Whatever it is, all of these computers collectively are part of your local area network. The type of logical addressing we use is called IP addressing and they look something like this. So, here's just one example. 192.168.4. oh, let's just say 100. Every device inside your local area network, whether it's wired or wireless, gets a unique address, which in this particular example, the first three numbers are the same. The last number has to be unique and different. Now, the other cool part is then we also have a router. Now I'm going to draw the router over here, although again, it's often in this same box. But this router is a member of our network also, and by convention we tend to give him the .1 address. It's not a law of physics, but that's the most common thing. So, the router itself has his own address. So, if any two computers want to talk to each other, they don't even really use the IP address, they actually just use their MAC addresses. However, if they want to talk to anybody that doesn't have an address that starts with 192.168.4, they have to send it out to this router. We call this router the default gateway. On the other side of this router is a totally different IP address, I'm just making these up, because this is a completely separate LAN. This is not our LAN. Here's an example of a typical home router. Now, I want you to take a close look at this. This particular one is for cable modem, so it's got my cable modem connection. This is another LAN that's being handled by my cable provider. This guy is wireless so he can do wireless connections and he even has a built in four-port switch out of convenience. So, it's a nice little thing. You don't have to go buy a separate switch. It's all built into this one little device and it makes our life great. Now, the only trick here is you have to enter this information. Now I'm going to save actually entering the information for other episodes. But before we part away from WAN, I want to answer one more question and that is, "Mike, I don't think I've ever actually had to type in these 192.168s or any of that stuff." That's right, because built into this device is a special kind of server called DHCP, which we'll cover in detail in other episodes, that when you fire up your computer and you join my wireless network, or you just light up and your plugged in, it automatically gives you all this information, making our life really, really easy. The big takeaway on this episode more than anything else is that every computer on Earth has got two very different addresses. There's a physical, or a MAC address, and that's for your local calls as you're just talking to each other. And then you have a logical address based on this numbering system called IP addressing. And I'm going to save all of those for lots of other episodes and other chapters.

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