DHCP servers operate independently, so you must install the service and configure scopes on every computer that will function as a DHCP server. The DHCP Server service is packaged as a role in Windows Server 2012 R2, which you can install by using the Add Roles And Features Wizard, accessible from the Server Manager console.
When you install the DHCP Server role on a computer that is a member of an Active Directory Domain Services domain, the DHCP Server is automatically authorized to allocate IP addresses to clients that are members of the same domain. If the server is not a domain member when you install the role, and you join it to a domain later, you must manually authorize the DHCP server in the domain by right-clicking the server node in the DHCP console and, from the shortcut menu, selecting Authorize.
After installing the DHCP Server role, you must configure the service by creating a scope before it can serve clients.
Creating a scope
A scope is a range of IP addresses on a particular subnet that are selected for allocation by a DHCP server. In Windows Server versions prior to Windows Server 2012, you can create a scope as you install the DHCP Server role. However, in Windows Server 2012 and Windows Server 2012 R2, the procedures are separate. To create a scope by using the DHCP snap-in for Microsoft Management Console (MMC), use the following procedure.
1. In Server Manager, click Tools, DHCP. The DHCP console opens.
2. Expand the server node and the IPv4 node
3. Right-click the IPv4 node and, from the shortcut menu, select New Scope. The New Scope Wizard opens, displaying the Welcome page.
4. Click Next. The Scope Name page opens.
5. Type a name for the scope into the Name text box and click Next. The IP Address Range page opens, as shown in Figure 4-8.
FIGURE 4-8 Configuring the IP Address Range page in the DHCP console
6. In the Start IP Address text box, type the first address in the range of addresses you want to assign. In the End IP Address box, type the last address in the range.
7. In the Subnet Mask text box, type the mask value for the subnet on which the scope will operate and click Next. The Add Exclusions And Delay page opens.
8. In the Start IP Address and End IP Address text boxes, specify a range of addresses you want to exclude from the scope. Then click Next to open the Lease Duration page.
9. Specify the length of the leases for the addresses in the scope and click Next.
The Configure DHCP Options page opens.
10. Select Yes, I Want To Configure These Options Now and click Next. The Router (Default Gateway) page opens, as shown in Figure 4-9.
FIGURE 4-9 Configuring the Router (Default Gateway) page in the DHCP console
11. In the IP Address text box, specify the address of a router on the subnet served by the scope and click Add. Then click Next. The Domain Name And DNS Servers page opens.
12. In the Server Name text box, type the name of a DNS server on the network and click Resolve or type the address of a DNS server in the IP Address text box and click Add.
Then click Next. The WINS Servers page opens.
13. Click Next to open the Activate Scope page.
14. Select Yes, I Want To Activate This Scope Now and click Next. The Completing The New Scope Wizard page opens.
15. Click Finish to close the wizard.
16. Close the DHCP console.
Once you have created the scope, all the DHCP clients on the subnet you identified can obtain their IP addresses and other TCP/IP configuration settings via DHCP. You can also use the DHCP console to create additional scopes for other subnets.
Configuring DHCP options
The New Scope Wizard enables you to configure a few of the most commonly used DHCP options as you create a new scope, but you can always configure the many other options at a later time.
The Windows DHCP server supports two kinds of options:
– Scope Options Options supplied only to DHCP clients receiving addresses from a particular scope
– Server Options Options supplied to all DHCP clients receiving addresses from the server
The Router option is a typical example of a scope option because a DHCP client’s default gateway address must be on the same subnet as its IP address. The DNS Servers option is typically a server option, because DNS servers do not have to be on the same subnet, and networks often use the same DNS servers for all their clients.
All the options supported by the Windows DHCP server can be either scope or server options, and the process of configuring them is basically the same. To configure a scope option, right-click the Scope Options node and, from the shortcut menu, select Configure Options.
This opens the Scope Options dialog box, which provides appropriate controls for each of the available options (see Figure 4-10).
FIGURE 4-10 The Scope Options dialog box
Right-clicking the Server Options node enables you to open the Server Options dialog box, which behaves the same way as the Scope Options dialog box.
Creating a reservation
Although DHCP is an excellent TCP/IP configuration solution for most of the computers on a network, there are a few for which it is not. DHCP servers themselves, for example, need static IP addresses.
Because the DHCP dynamic allocation method allows for the possibility that a computer’s IP address could change, it is not appropriate for these particular roles. However, it is possible to assign addresses to these computers by using DHCP, using manual, instead of dynamic, allocation.
In a Windows DHCP server, a manually allocated address is called a reservation. You create a reservation by expanding the scope node, right-clicking the Reservations node, and, from the shortcut menu, selecting New Reservation. The New Reservation dialog box opens, as shown in Figure 4-11.
FIGURE 4-11 Creating a reservation
In this dialog box, you specify the IP address you want to assign and associate it with the client computer’s MAC address, which is hard-coded into its network interface adapter.
It is also possible to manually configure the computer’s TCP/IP client, but creating a DHCP reservation ensures that all your IP addresses are managed by your DHCP servers. In a large enterprise, where various administrators might be dealing with DHCP and TCP/IP configuration issues, the IP address that one technician manually assigns to a computer might be included in a DHCP scope by another technician, resulting in potential addressing conflicts. Reservations create a permanent record of the IP addrss assignment on the DHCP server.
The Windows operating systems include a DHCP client that can configure the local IP address and other TCP/IP settings of computers with an operating system already installed. However, it is also possible for a bare metal computer—that is, a computer with no operating system installed—to use DHCP.
The Preboot eXecution Environment (PXE) is a feature built into many network interface adapters that enables them to connect to a DHCP server over the network and obtain TCP/IP client settings, even when there is no operating system on the computer. Administrators typically use this capability to automate the operating system deployment process on large fleets of computers.
In addition to configuring the IP address and other TCP/IP client settings on the computer, the DHCP server can supply the workstation with an option specifying the location of a boot file that the system can download and use to start the computer and initiate a Windows operating system installation. A PXE-equipped system downloads boot files by using the Trivial File Transfer Protocol (TFTP), a simplified version of the FTP protocol that requires no authentication.
Windows Server 2012 R2 includes a role called Windows Deployment Services (WDS), which enables administrators to manage image files that remote computers can use to start up and install Windows. For a PXE adapter to access WDS images, the DHCP server on the network must have a custom PXEClient option (option 60) configured with the location of the WDS server on the network.
The PXE client on the workstation typically needs no configuration, with the possible exception of an alteration of the boot device order so that the computer attempts a network boot before using the local devices.
In a properly configured WDS deployment of Windows 8.1, the client operating system deployment process proceeds as follows:
1. The client computer starts and, finding no local boot device, attempts to perform a network boot.
2. The client computer connects to a DHCP server on the network, from which it obtains a DHCPOFFER message containing an IP address and other TCP/IP configuration parameters, plus the 060 PXEClient option, containing the name of a WDS server.
3. The client connects to the WDS server and is supplied with a boot image file, which it downloads by using TFTP.
4. The client loads Windows PE and the WDS client from the boot image file onto a RAM disk (a virtual disk created out of system memory) and displays a boot menu containing a list of the install images available from the WDS server.
5. The user on the client computer selects an install image from the boot menu, and the operating system installation process begins. From this point, the setup process proceeds just like a manual installation.
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