Introduction to TCP/IP

- I'm gambling that most of us out here have heard the term IP address. So I'd like to start off by showing you what would be a typical IP address you might see on a computer today. So here's 192.168.5.10. Does that look familiar to you? These four digits separated by three dots? What we're looking at are the addresses that help us get information to any computer on the internet. Without these IP addresses, the internet's not going to work. But to really understand how all this started we got to go way back in time. Back in a time when we wanted big networks but we didn't have one yet. And what we're going to start with is here in the United States. Here's a map of the continental United States. So here there's Maine, and Florida. So if we got, you know what, wait a minute. We're going to do this live. Forget about it. Okay, let's do this with me in front of you 'cause I love talking about this stuff. So here's our map in the United States. (humming) I'm from Texas, there's Florida. All right, so here's a map of the United States. Now, all around the United States are military installations and there was military installations, there was also a lot of universities. The idea is that we had all over the United States thousands of local area networks and we wanted to interconnect these local area networks so that anybody in one LAN could talk to another LAN, get the idea? So we would have connections, the LAN up here in Chicago and a LAN over here in San Jose, LAN over here in Boston, LAN down here at Rice University in Houston, somewhere in northern Florida. The idea here is that we would have these individual LANS and we want to connect them. Now we're talking the late 1970s, early 1980s here. So these were connected through basically telephone lines back in the old days. And this was being designed by an organization called ARPANET or ARPAT is the same organization today. And the idea is that we would create multiple connections to these individual nodes which would then act to help other nodes. And more importantly, if any of these nodes went down, if this one went kaboom, we could reroute this information and it would still get to everybody. Now the problem is, is we need some kind of numbering system to organize all this. Now, they were coming up with this numbering system back in the late 1970s, early 80s, and they were thinking, well, you know, one day there could be, you know, 10, 20,000 computers on this thing which we're eventually going to call the internet. So we need to think big. Yeah, they didn't think that big. So basically what you have is you've got four numbers. So I'm going to say for this example, I'm going to say 10.11.12.13. Each one of these values called an octet can go from zero to 255. All the different combinations come up to around 4 billion addresses. And back in the late seventies, early eighties, they go, "This is going to be great." Now keep in mind, every computer on this thing which will eventually be called the internet must have its own IP address but not just its own IP address. We're going to have all of these LANS all over the place. So this number is going to do two things at the same time. Number one, it's going to identify which local area network you're a member of. And number two, it's going to give you a unique, what we call host ID that's unique only to you, got it? All right. So the whole idea between taking these and breaking 'em into four groups with three dots is that we would have what was called tier one of the internet. Now this was the original plan and there would be some local area network here, a router, and he would be called the 10 router. And then this router over here at Rice University in Houston would've been called the 12 router. I am making these numbers up but this is basically how it happened. Then over here in San Jose, this would be the 6 router. Well, Mike, why didn't they do 1, 2, 3, 4? Because they're computer nerds and they, this guy over here liked the number six. There was no rules. It was wild west back then. All right, so this is kind of the basic idea. Now what I'm going to do now is I'm going to concentrate on Rice University. That's Galveston Bay. There's Galveston Island, this is the southeast coast of Texas. Here's Houston and right about here is Rice University. So Rice University is going to be 12. Now, the problem here is that there's a lot of people in the Houston area who also want to be connected to this thing, which will eventually be called the internet. So what will happen is say, over at University of Houston, University of Houston instead of connecting to the big top part, they're going to get their own little router. And Rice University is then going to call that router 12.1. Now here's the important thing. Anybody who hooks to the 12 router, their IP address will start with a 12. Now, it's up to the folks here at Rice University to delegate down to whoever needs it. And back then this was all free and everybody loved each other and this stuff was easy to get. So, now all of a sudden, University of Houston is 12.1. Well, there's a lot of computers at University of Houston. They've got the parallel processing center, they've got the engineering college, they've even got an art college, and I don't know those artsy types, they want to have their own little local area network as well. So what we're going to do from there is we're then going to start passing out, so the parallel processing, they're going to be 12.1.44, again, nobody ever did these in order, just out of cruelty I think. And then over here it's going to be 12.1.27. And those crazy art people, well they're going to be 12.1.28. There we go. Now, notice these numbers are all different. These are all separate local area networks. Now we've got one more digit, right? Well that last digit is for the individual computers. So what would happen is that this one little local area network here would have the network ID of 12.1.44 and then the individual computers would be 1, 2, 3, 4, 5, 6, all the way up to 254 because you cannot use zero or 255. And in other episodes we'll explain why that happens. So there is a little bit of limitation, but not much. So the whole idea behind the whole internet was going to be what we call aggregation. And it didn't quite pan out that way because sometimes other people, like another Comcast would come in and put a different kind of numbering system in. But the bottom line is that it works. Now what's interesting is that they designed this in such a way that it had a lot of flexibility. So for example, if you needed an IP address, oh by the way you don't just type these into your computer. These are allocated to you by the internet authorized numbering authority, they're IANA. And the idea is that no two computers on the internet can ever have the same IP address. So you don't just magically type this in. Somebody from on high passes you down a block of addresses. So for example, you would call up, if you're at University of Houston, you'd call up the U of H people and they would allocate something 12.1. whatever. If University of Houston wanted even more then they'd call up Rice University and Rice University would give them a 12.3 or whatever was next on the list, you get the idea? So you always came down from on high and got yourself a block of addresses. Any block of addresses where the first three numbers are set and you can do anything you want on the fourth number, we call those Class C. If you get a block of addresses, now there's another limitation here, I'm going to avoid this for the moment. And the first two numbers are locked, it's a Class B. And then if the first number is locked and you get to do whatever you want with the last three then we call it a Class A. If you have a Class C address, you have 254 hosts you can have in that local area network. If you have a Class B, you get 256 on 256, about 65,536. And if you've got a Class A, it's in the millions. So most of the time the people who got Class A's were people like Rice University or somebody they knew they were going to pass it down to. The bottom line is, is that we live in a world where IP addresses are based on the idea that you're always going to be no more than four routers away from the top of the internet and boy did they make a mistake there. So the total address space of the IP addressing was about 4 billion IP addresses. But the problem is a lot of them were wasted on all kinds of dumb stuff. Like for example, no address can end with 255, so that gets rid of a bunch. Or you would have certain addresses, like anything that started with one was experimental. They called it reserved and nobody could use them. So there was lots of limitations. 4 billion sounds like a lot even in today's world but it was nowhere near enough. You're going to have to watch other episodes to see how we snuck around this limitation 'cause we've done a pretty good job of it. Right now what's important to me is that you understand the nomenclature of an IP address. So let's make sure, we have four characters and these characters go from zero to 255. You will have three dots in between them and watch out on the exam, they will actually have examples up where they'll have an IP address and it'll have like 257 in it or something like that. And they're going to say which of these four is valid, not the one with 257. Also keep in mind that addresses never end with a zero or a 255 and we'll save that for other episodes to make you understand why that exactly is. With IP addressing, we're going to add something to our frame here. So what I'm going to do is now add in the destination IP address and the source IP address. This is going to allow us to jump from local area network to local area network. So to actually watch all this in action, let's zoom in a little bit and I'm going to concentrate on just two small local area networks that just happen to be connected together with the same router. I've got two local area networks here. Now there's a switch in here, I'm going to draw some computers. I'd just like to draw a circle to show you what the network ID is. Inside every one of these computers I have entered a value that starts with 10.11.12. something. So we put a zero on the end to show that we're not talking about a computer, we're talking about a network ID. So that's one of the reasons we can't put a zero on the end of an IP address 'cause it identifies an entire LAN. So this computer right here might be 10.11.12.44 and this one right here might be 10.11.12.222. Those numbers get in there because somebody typed them in. Every operating system has a place for us to enter these values. Now over here on this other network which is 10.14.6.0, I'm just going to draw one computer in here and he's going to be 10.14.6.7. So let's get some communication going. Now, if this computer over here, 10.11.12.44 wants to talk to 10.11.12.222, what's he's going to do is he's going to take a look at the IP address where he's sending it to and he's going to compare it to something called a subnet mask. This is another value that you have to enter into your computer. So a subnet mask usually looks something like this, 255.255.255.0, wherever you see a 255, the numbers have to be the same. Wherever you see a zero, the numbers can be different. So let's compare these two addresses. They're both 10.11.12 and only the last digit is different, correct? So by looking at the subnet mask, that's how your computer calculates this, he knows something very important. He knows that that other address is in his local area network. That easy. Just by comparing the address he's sending it to with his own IP address. That way he could go ahead and put on the proper Mac addresses and just send it right over to that computer. It's a local call as we say. Now let's change the story a little bit. Now we've got a computer over here, 10.14.6.7 and this computer over here wants to talk to him. Now when he takes a look at that address which is going to be 10.14.6.7, you'll see the 10 matches. That's great, but the next two digits don't match. This means it's not on his LAN. Luckily, any computer that's connected to the internet is part of a network that also has this router thing connected to it. And a router is going to have an IP address which is part of this network and it's usually going to be 10.11.12, almost always we call the router .1. It's just etiquette, it's not a law of physics. So what will happen is when 44 sees that he can't talk to this guy directly, what he does instead is he sends it to 10.11.12.1. So this computer, this router acts kind of like a gateway to the internet. In fact, that's what we often call this. We call it the default gateway. So if you want a computer to be on the internet, you're number one, going to have to give it an IP address. Number two, you're going to have to give it a subnet mask. And number three, you're going to have to give it a default gateway. The subnet mask is only there to let your computer know if it's a local call or a long distance call. And if it's a long distance call it sends it to the default gateway. Where do we type in this IP address, and subnet mask, and default gateway? How do I enter it? Well, you're going to have to wait for the next episode.