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Now that we've installed the DHCP server service we want to take a moment to understand, how our clients would be getting IP addresses from that DHCP server. And the way that this happens, the way that your machine gets an IP address if it's a DHCP client, is through the DHCP lease process and the lease process works with a 4 packet conversation between client and server. The conversation entails a discover packet, an offer packet, a request packet and an acknowledgement packet, dora, if that helps you remember dora. To help illustrate this, I'm going to get out the Paint pad here and I'm going to make in this network a DHCP server and I'm going to make a DHCP client and I'm not going to label it because it takes too long. So you will just have to trust me that this is a DHCP client. DHCP client at boot-up time has no IP address. It has an IP address of all zeros if you will. It will try to find a DHCP server somewhere in the network by sending out a discover packet. And this discover packet, what I want you to understand about is that it is broadcast. It is sent out to all computers in the network. It's sent out to an address of 255.255.255.255 that is just a general broadcast, and if you remember from earlier in the module, we specified that 255 designates under most circumstances, a broadcast. So all 255s is where this thing is going to, the source if you would look at is 0.0.0.0. Any DHCP server which is listening for the BOOTP protocol will then respond with an offer and the offer packet is sent out in response to the discovery and the offer packet contains the offer IP address, you can have this IP address and so on. So the client then after it receives the offer says, Okay, sure I'll take that IP address and it will take the first one it receives. So if there's two DHCP servers out here, remember they will both receive the discover because it's a broadcast packet, but the first one to respond will be generated the request and the first DHCP server to respond with the offer will have that offer responded to with the request. So this is the 3rd packet in the conversation, the request. The request says here's the IP address I'd like, it'll be the same one that was offered and so on and so on and here is the ID of the server who offered it to me. So that way it is also broadcast out by the way, that way this DHCP server knows that its offer has not been accepted and it can't leave the IP address in its DHCP pool. In its pool of IP addresses. The last part of this conversation is the acknowledgement and the acknowledgement just really verifies that this client is going to take this IP address. This is set from DHCP server to DHCP client this is also by the way at this time still a broadcast packet, because until this acknowledge happens this client still doesn't have an IP address. So this packet contains in it the offered IP address, the identifier of the server who's doing the offering and then any other optional information, which can include the address of the default gateway, DNS servers, Win servers and on and on. So any other optional information that's configured with DHCP, which will do is contained in that acknowledge packet. What's also significant about that acknowledge packet is by identifying the server who did the acknowledge, who did the lease, then come renewal time it's not broadcast based. We just go straight to the source and say can I renew please, n e w, can I renew that IP address. So the broadcast only affects the network for a short period time and it's not a whole lot of traffic. So generally speaking over the course of a day or a week the traffic that's going to pass between DHCP client and DHCP server is very, very minimal. So what I hope you have heard so far from this module is that in the DHCP lease process all packets are broadcast based. Well not all routers, not all networks with multiple subnets support passing of broadcast traffic. How do we deal with that? We'll find out in modules to come.