Understanding IP addresses - Windows Server Tutorial

- [Instructor] Understanding how IP addressing works. One of the first things that you need to make sure you have a good grasp on is what exactly an IP address is. Now I know you can ask pretty much anybody at this point and they know what an IP address is. It's a bunch of numbers that represent a computer on a network so it can talk to other computers. While that's not necessarily wrong, we need to understand it in a little more detail than that. So if we go through a true definition of what is an IP address, first of all it is a 32 bit address that is used to uniquely identify a computer on a network. So while it looks like... Typically you'd look at an IP address as a bunch of... You know it's like four numbers with a bunch of dots between em. To the computer itself, it's actually binary, which means it's a bunch of ones and zeros. And, to be more specific, it's made up of 32 ones and zeros. So that's what we mean by 32 bit address. Now another interesting thing about an IP address is that even though it looks like four numbers, it's actually made up of two components. One component is the network ID and this is the portion of the address that determines what network the computer is on. And then the other is the host ID and this is a unique identifier on that particular network. Many people will analogize this with a street address. Alright so if you think of your street address, if you live at 123 Main Street, you have two components there as well. You have the street that you live on and that would be like the network ID. What network you're on is like what street you're on. And then you have 123 which was the number. So we have Main Street, that's what street we live on, and we have 123, that's the actual unique identifier to your building on that street and that would be like the host ID. Let's take a look at an actual example here and see if we cannot break it down. Here I have the IP address 192.168.10.1. A fairly common IP address that we see out there. One thing that we know right out the gate is that in an IP address the network ID is always on the left side. So the left side of the IP address is the network ID and the right side is the host ID. That we know. So it's kind of almost a reverse from the street address because the street address we kind of have the host ID first followed by the network ID. Here the network ID is to the left, the host ID to the right. But what we don't know when we look at an IP address all by itself, we don't know where we draw that line. How much of the IP address is on the left and how much is on the right. So what we need to add to every IP address when we're configuring it is something called a subnet mask. And the subnet mask, typically you see it made up of just two numbers. Either 255 or zero. And if you've ever paid attention, you may have noticed that the 255, whether it be one, two, three of them, whatever it may be, is always on the left and the zero or zeros is always on the right. And the reason why is because anywhere there's a 255 that is signifying the network ID portion of the IP address and anywhere you see the zeros that represents the host ID. So in this example, what that means is that 192.168.10 is the network that this computer would be on and then the unique identifier for that network is just simply one. If we were to change the subnet mask to 255.255.0.0, then that means that the network ID is just 192.168 and the host ID is 10.1. And, of course, if we change it once again so that's it's 255.0.0.0, now the network ID is 192 and the host ID is 168.10.1. So the subnet mask is significant to determining what portion of the IP address is the network ID and what portion is the host ID. And the reason this is important is because in order for computers to talk to one another, they have to be on the same network. So they all have to have the same network ID. And if they're on that same network, well then they all have to have a unique host ID. Up on the screen here, I have a nice simple network. You picture in your network very often you have servers and you have clients and they all talk to some firewall to get out to the Internet. In this example, you'll see that each one of the items on the list here, the server, the client, and the router, they all have an IP address, they all have a subnet mask to go with it, and I've actually added a third item which says DG which stands for default gateway. So you can see that all three have this information. Now I'm not going to go into detail on the default gateway right now. But for the most basic sense of what it is, any particular system when you are configuring its IP address, you give it the IP address of a default gateway which is where that computer should go if it wants to communicate outside of its network. So if we said in order for these computers to talk to one another they need to be on the same network. If they want to talk to a computer on a different network, they have to go to their default gateway which is a router. So that's why you'll notice the client and the server both have a default gateway pointing to the IP address of the router in this example. Whereas the router doesn't have a default gateway because it's a router. Let's get back to the IP address portion. You'll notice that they all have an IP address and they all have the same subnet mask of 255.255.255.0. That means that the network ID for all three of these is 192.168.10. So they're all on the same network which means they can all talk to one another. But they can only do this if they have a unique host ID on that network. So let's look at the other portion and you'll notice that the server has 201, the client has 101, and the router has 200. In the event that there was a duplicate, let's say that there was another client and it also had the host ID of 101, then you would end up with a conflict and they would not necessarily be able to communicate on the network. It'd be kind of like on your street if multiple buildings had the same number, then the postal carrier wouldn't know how to drop off the mail. He'd look at the address and say "I don't know. There's two buildings on the street with the same number. What do I do?" Alright, so that is the basics when it comes to understanding the actual makeup of an IP address. It's a 32 bit number. I know we didn't get into the binary here. I'll get into that in another video. But these numbers actually represent a 32 bit binary number and we know that the IP address is made up of a network ID on the left and a host ID on the right. And in order for everything to communicate, then they all have to be on the same network and have a unique ID on that network.