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DHCP is a topic that you're guaranteed to see questions on the 70-642 exam so let's go through it now and give you just a real brief overview of what it is and kind of some gotchas and things you need to be aware of for the exam. Most of this is just pure, basic DHCP. Now, first of all, DHCP means Dynamic Host Configuration Protocol and it means just exactly what it says. If every computer on our network has to have a unique IP address, a network ID or a subnet mask and a default gateway and DNS information and so forth, then we need some way to configure that stuff. Now, in the early days of networking, we did every machine manually and they had static addresses that never changed. This was a huge pain because administrators would fat finger addresses and things wouldn't work. We would inadvertently give two machines the same IP address and they didn't report that back in. They would just intermittently work or not work and this was a problem. Now, what's interesting is early on and gosh, this would have been ten, fifteen years ago, we saw DHCP as a security risk and wouldn't use it until it kind of grew up and then we realized as our networks got larger and larger, this was where we were going to have to go with it and it was actually more secure because once we got it working, it just worked. So this is ultimately automatic configuration of your IP address, your subnet mask and any other information. Not any other but a lot of other information that you'll need to put on that machine. Now, this requires for DHCP to work, it means you must have a DHCP server on the subnet with that user's computer because as you'll see in a minute, the user's computer's going to broadcast when it starts up. Now, if your client is not on the same subnet as the DHCP server, you'll have to have a relay agent and the relay agent will see that broadcast for a DHCP server and it will pass that request through a router to a DHCP server and then kind of work on behalf and proxy that back and forth. We'll get into that in a different video. Now, the way we set up a DHCP server is it is a Windows Server 2008 role and in a different video we'll actually go through this process and add that role in just so you can see what that looks like. OK? So we're looking at a Server 2008 role and it's going to automatically configure our clients for us. Now, let's look kind of in it with a little diagram here about what's happening. So a user comes in in the morning, they flip their computer on and as it boots up, we have a DHCP server out on the network on that subnet where that user is. Or we have a way for them to reach the DHCP server. So as it's coming up, it broadcasts and what it is actually passing is a DHCP discover packet and you do need to know these four steps for the exam. So the first step is the client machine broadcasts a DHCP discover message. The DHCP server sees it and it responds with a DHCP offer. It's basically saying oh, wait. Here I am. Yeah, I can take care of you. Now, the reason we're doing this is because there could be two DHCP servers that hear this broadcast and we want to make sure that we don't step on each other or assign two IP addresses or any of that kind of stuff. So the DHCP server responds with a DHCP offer and then the client responds back saying OK, yeah, I'll do business with you. Go ahead and send me some information, send me some configuration information for the subnet that I'm on. And the server sends it back and it is called a DHCP ack or acknowledgement. OK? So that's the four steps: discover, offer, request and ack. Make sure you know those before you go sit the exam because you will see questions about that. Now, a DHCP server, once we set this up, it is actually a list or a small database of addresses that we can give out to clients. Now, the way it's arranged is in scopes. There can be one or more scopes on a DHCP server. Now, a scope is simply a range of IP addresses based on a single subnet. So we might have, you know, 15.1.10.0 to 15.1.0.255; so all those addresses could be handed out. We can also provide subnet masks to hand out and we can provide default gateway information to hand out and we can also tell it whether it's a subnet, what subnet type and we can check that and what we're going to do here is give out the address for different amounts and times. If it's wired or you're on a wired network, then it's like six days, seven days, I'm going blank here, OK? But on a wireless network it's like eight hours. OK? So what you need to know really here is that the wireless network is in a matter of hours because we want that address to expire and the computer to drop off the network if it can't renew it. Now, here's the thing you have to watch. Notice it's in all caps. Once you create the scope in the DHCP server, you have to activate before it will answer DHCP discover packets and actually offer and provide addresses. So the scope has to be activated. If you go in and deactivate the scope, it will stop providing addresses. Now, you can also set options and you'll see this again a little bit later on but this is where we get that additional configuration data; DNS server addresses, WIN server addresses and so forth and there's actually over 60 addresses you can give out out there, other information you can give out along with the basic DHCP information. So that's the basics of DHCP. Coming up in a couple of other videos we'll go set up the role and look at some of these options and classes and talk about some exclusions and reservations and just kind of get you well rounded on DHCP.