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When you configure a Windows Server 2003 machine to use an IP address, you have two choices about how to configure that address. One is that you can assign the IP address statically or dynamically. In dynamically we'll use the services of DHCP, Dynamic Host Configuration Protocol, which we talk about later on in the chapter. Now you don't necessarily have to have the DHP server on hand as you may be well aware, there are lots of devices like small office and home office routers that also provide the services of DHCP, a scaled down version of DHCP, to assign an IP address. When you install Windows Server 2003 you are automatically configuring DHCP, configuring that computer to be a DHCP client. And so set this from the properties of my network places this is the network connections applet in control panel, look at the properties of the connection you are configuring, TCP/IP properties and here are your two ways again, obtain an IP address automatically uses a DHCP server, Dynamic IP addressing or specify the following IP address and then you enter in the information manually. We've looked at both of these things, we've looked at how to enter a static IP address earlier but we just we want to reiterate here, that there are two ways, you either type it in automatically or you use dynamic IP address allocation scheme using DHCP. Now if you are a DHCP client and you are unable to locate the DHCP server, you get your IP address from a range of IP addresses known as automatic private IP addresses or APIPA addresses. The test certainly wants you to know about APIPA although you shouldn't run into too many APIPA addresses, at least on the server, you may experience this several times on the client side. APIPA occurs or you get an address from the APIPA range when you are unable to find a DHCP server and you are a DHCP client. You can't get an IP address automatically, you get one from this range. You get one from the range 169.254.x.y and your subnet mask is 255.255.0.0. So it is a class B address, it is a private IP address range, in other words, you won't find another computer attached to the public Internet that uses this IP address range, uses this class B address and what happens is your computer picks a number at random from the 65000 available here, and then broadcasts it on the network. If that IP address is in use, then whoever has it says, no I've got this IP address, if it's not in use, then it binds this IP address to the network adaptor and periodically sends out requests for a DHCP address. So if that DHCP server comes back online, you should automatically with in a matter of a couple of minutes get an IP address from that DHCP server. By the way this is not new to Server 2003, this is something that has been around since Windows 98 days. Computers would automatically assign themselves IP addresses. What you need to make sure and understand is what are the symptoms, or what are the behaviors associate with APIPA addresses. Here are the behaviors. One the client is able to communicate with other computers on a local network and that's because it's assumed that those DHCP clients as well have also gotten an IP address that's in that APIPA range. But it's unable to communicate with remote networks. Why is it unable to communicate with remote networks? Well notice here that an IP address is assigned a subnet mask is assigned but APIPA does not assign a default gateway. So what does that mean? The computer without a default gateway cannot pass packets to remote networks. So these are really the two behaviors and then if you were to type IPconfig/all, IPconfig/all, it would reveal that indeed your IP address starts with 169 and that you're getting your IP address or that your client type is auto configured. Now you may be wondering why does APIPA exist in the first place? Well it makes things very easy to work with right out the box. You can set up a room of computers you don't need to setup DHCP, you don't need to have a router there to provide services of DHCP, yet that room full of computers can still talk to one another. If the DHCP server is available, your clients get an IP address from that service, but if not we can still just kind of throw a bunch of computers in a room, hook them up together and they can all talk to each other. So that's the advantage of APIPA, it makes peer-to-peer environments, very, very easy to setup.