Windows 7 / Networking

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Deploying a DHCP server

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, which you can install 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 also 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 2012, you can create a scope as you install the DHCP Server role. However, in Windows Server 2012, the procedures are separated. To create a scope using the DHCP snap-in for Microsoft Management Console (MMC), use the following procedure.

1. Log on to Windows Server 2012 using an account with Administrative privileges. The Server Manager window opens.
2. lick Tools > DHCP. The DHCP console opens.
3. Expand the server node and the IPv4 node.
4. Right-click the IPv4 node and, from the shortcut menu, select New Scope. The New Scope Wizard opens, displaying the Welcome page.
5. Click Next. The Scope Name page appears.
6. Type a name for the scope into the Name text box and click Next. The IP Address Range page opens.
7. In the Start IP Address text box, type the first in the range of addresses you want to assign. In the End IP Address box, type the last address in the range.
8. 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 appears.
9. In the Start IP Address and End IP Address text boxes, specify a range of addresses you want to exclude from the scope. You can also specify a delay interval between the server's receipt of DHCPDISCOVER messages and its transmission of DHCPOFFER messages. Then click Next to open the Lease Duration page.
10. Specify the length of the leases for the addresses in the scope and click Next. The Configure DHCP Options page opens.
11. Select Yes, To Configure These Options Now and click Next. The Router (Default Gateway) page opens.
12. 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.
13. 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.
14. Click Next to open the Activate Scope page.
15. Select Yes, To Activate This Scope Now and click Next. The Completing The New Scope Wizard page opens.
16. Click Finish to close the wizard.
17. Close the DHCP console.

Once the role installation is completed, all of the DHCP clients on the subnet identified in the scope you created 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 scope option, because DNS servers do not have to be on the same subnet, and networks often use the same DNS servers for all of their clients.

All of 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. The Scope Options dialog box, which provides appropriate controls for each of the available options.

Right-clicking the Server Options node enables you to open the Server Options dialog box, which behaves in exactly the same way.

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. Domain controllers, Internet web servers, and DHCP servers themselves 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 still possible to assign addresses to these computers with 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.

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.

Of course, it is also possible to manually configure the computer's TCP/IP client, but creating a DHCP reservation ensures that all of 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 address assignment on the DHCP server.