Running DHCP Clients and Servers

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from Chapter 14, Windows NT Administrator's Pocket Consultant by William R. Stanek.

DHCP (Dynamic Host Configuration Protocol) is designed to simplify administration of Microsoft Windows NT 4.0 domains, and in this chapter you'll learn how to manage it. You use DHCP to dynamically assign TCP/IP configuration information to network clients. This not only saves you time during system configuration but also provides a centralized mechanism for updating the configuration. To enable DHCP on the network, you need to install and configure a DHCP server. This server is responsible for assigning the necessary network information.

Understanding DHCP

DHCP gives you centralized control over IP addressing and more. If the network has a DHCP server, you can assign a dynamic IP address to any of the network adapter cards on a computer. You do this by using the Identification tab of the TCP/IP Properties dialog box. Once DHCP is set up on a computer, you rely on the DHCP server to supply the basic information necessary for TCP/IP networking, which can include

• IP address, subnet mask, and default gateway

• Primary and secondary DNS servers

• Primary and secondary WINS servers

The DHCP Client and the IP Address

A computer that uses dynamic addressing is called a DHCP client. When you boot a DHCP client, an IP address is retrieved from a pool of IP addresses defined for the network's DHCP server and assigned for a specified time period known as a lease. When the lease is approximately 50% expired, the client tries to renew it. If the client can't renew the lease, it will try again before the lease expires, and if this attempt fails, the client will try to contact a new DHCP server. IP addresses that are not renewed are returned to the address pool. If the client is able to contact the DHCP server but the current IP address can't be reassigned, the DHCP server assigns a new IP address to the client.

Installing a DHCP Server

Dynamic IP addressing is only available if a DHCP server is installed on the network. Once a DHCP server is installed, you use the DHCP Manager utility to configure and manage dynamic IP addressing on the network. On a Windows NT server, you use the following steps to allow it to function as a DHCP server:

1. Access the Services tab of the Network Control Panel utility and then click on the Add button.

2. Choose DHCP Server in the Select Network Service dialog box and then click OK.

3. Now you'll need the Windows NT distribution CD-ROM. When prompted, insert the disk and then enter the path for the distribution files, such as: e:\i386\. Click Continue.

4. Click OK at the prompt. If any of the server's network adapter cards currently uses dynamic addressing, Windows NT opens the TCP/IP Properties dialog box and you'll need to set up static IP addresses.

5. When you close the Network utility, the DHCP server is installed and you'll need to restart the computer.

From now on, the Microsoft DHCP Server service should start automatically each time you reboot the server. If it doesn't start, you'll need to start it manually with the Services utility in the Control Panel.

Tip A single DHCP server can provide services to multiple network segments. However, DHCP relays must be configured to forward DHCP messages to the server. Configuring DHCP relays is covered in the section of Chapter 12 titled "Configuring DHCP Relays."

from Windows NT Administrator's Pocket Consultant by William R. Stanek. Copyright © 1999 Microsoft Corporation.

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