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Address Blocks is a term that you may see on the exam and I just want to explain what an Address Block is - it's actually pretty simple, but like most things in TCP IP you have to back up a couple of steps to explain it, so here we go. A couple of other things that you're going to see on the exam as well which you need to be aware of and so I've just kind of lumped them all into this video to help you. First of all there are two types of IP addresses. Now in all of this keep in mind we're talking about IPv4, which is the IP, the version of IP that we're working with right now. We'll talk about IPv6 in a later video and explain what's going on with all that. So for now the first type of IP address is Public Address and then, of course, the Private Address. Pretty simple, right? Well, let's talk about the differences between the two of these. First of all Public IP addresses are those that we get from an ISP, or an Internet Service Provider. We call them up and we say hey, I need a public IP address and we pay for it and this is where we get our domain name and all that kind of stuff. We're tying an IP address that's registered out there back to a domain name, OK? Now, you're going to have one Public IP address for every computer that's directly connected to the Internet. Now, the word Block, or an Address Block, this is where this actually comes in, this is the group of IP addresses sharing a single network ID because sometimes you may call the ISP and say, hey I'm going to connect my web server to the Internet and so I need just one IP address. And in other situations you're going to connect a bunch of computers to the Internet and so they're going to give you a block, or a network ID with a certain number of host IDs along with it, or a section of a network and that's called a block of addresses, OK? Now, the Address Space - you'll hear that term - that is those individual IP addresses, host addresses, inside that block that you got. So an Address Space would be individual addresses inside a block and the block is a group or a range of IP addresses that share a single Network ID and those are Public and those will connect to the Internet, they'll be registered out there and they'll be in the DNS records. Now, let's take a look at the Private side of it and you need to watch for this on the exam. Private you can freely assign these however you want to in your Private network. Now there are three ranges that are used that were designed for this purpose and so you see these all the time. Notice from 10.0.0.0 through 10.255.255.254 any address within that range, that means 10.1.1, 10.1.2, 10.1.3 all the way up to 254 up through 10.2.1, 10.3.1, so you can see there are quite a few in there. So, all of those are Private. Now when we see these Private addresses even if you tried to throw this address out on the Internet the routers won't mess with these because they're designated as Private. The other range of Private addresses, 172.16 through 172.32.255.254 and then the last one, probably the most famous one, 192.168.0.0 through 192.168.255.254. If you've ever gone and bought a wireless router for your home you will notice that it normally has 192.168.0.0 as its address, or .1 as its address, OK? So, anyway, those are the Private addresses. Now, be careful because you will see these in various forms on the exam and when you see any of these addresses on the exam pretty much if you see a 10 or 172 or a 192.168 on the exam you're looking at a Private address and it's going to be inside the network, not a Public address connected to the Internet, OK, so just keep that in mind. And also remember that they will probably never ask you straight up, is this a Public or a Private address. They will use at scenario and you'll have to understand it to know why some things aren't working. OK, so that's just some more nomenclature, some little gotchas to watch for on the exam, some other things to be aware of in the world of TCP IP.