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Configuring Dynamic Host Configuration Protocol (DHCP)

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The Dynamic Host Configuration Protocol (DHCP) is a protocol that allows administrators to manage and automate the assignment of IP addresses in a centralized console. Without DHCP, the IP address must be “statically” configured on each computer. This isn’t such a big deal in a small (ten client-or-less) environment, but when you get into significantly larger environments, static IP address management can become a nightmare. Factor in the mobility of using laptops, and the need to be able to connect to other networks dynamically, and you’ll find it’s almost impossible in today’s world not to use DHCP.

The way DHCP works is fairly simple. Using a client/server model, a DHCP server maintains a pool of IP addresses. DHCP clients request and obtain leases for IP addresses during the boot process. DHCP was derived from the Bootstrap Protocol (BOOTP), which was a protocol typically used to allow clients to boot from the network rather than from a hard drive. Through this boot process, BOOTP assigned an IP address dynamically to the client computer. Some benefits of using a Windows Server 2008 DHCP server include:

DNS integration. Windows Server 2008 DHCP integrates directly with DDNS. When a computer obtains a lease for an IP address, the DHCP server can then register or update the computer’s Address (A) records and pointer (PTR) records in the DNS database via Dynamic DNS on behalf of the client computer. The result of the two—DHCP used with DDNS—is true dynamic IP address management. Any computer can start up on the network and receive an IP address that is further registered in the DNS name server.

Multicast address allocation. The Windows Server 2008 DHCP can assign IP addresses to multicast groups in addition to the standard individual hosts. Multicast addresses are used to communicate with groups such as server clusters using network load balancing.

Detection of unauthorized DHCP servers. By restricting DHCP servers to those that are authorized, you can prevent conflicts and problems on the network. An administrator must configure Active Directory to recognize the DHCP server before it begins functioning on the network. The Windows Server 2008 DHCP service contacts Active Directory to determine whether it is an authorized DHCP server. Active Directory also enables you to configure which clients a DHCP server can service.

Enhanced monitoring. With the Windows Server 2008 DHCP service, you have the ability to monitor the pool of IP addresses and receive notification when the address pool is utilized at a threshold level. For example, you might monitor for a threshold of 90 percent or above.

Vendor and user classes. Vendor and user classes enable you to distinguish the types of machines that are obtaining DHCP leases. For example, you can use a predefined class to determine which users are remote access clients.

Clustering. Windows Server 2008 DHCP services support clustering. Through a cluster, you can ensure a higher reliability and availability of DHCP services to clients.

The negotiation process consists of only four messages, two from the client and two from the server. The first message is the DHCP Discover message from the client to the server. This message looks to a DHCP server and asks for an IP address lease. The second message is the DHCP Offer message responding from the server to the client. A DHCP Offer tells the client that the server has an IP address available. The third message is a DHCP Request message from the client to the server. In this message, the client accepts the offer and requests the IP address for lease. The fourth and final message is the DHCP Acknowledge message from the server to the client. With the DHCP Acknowledge message, the server officially assigns the IP address lease to the client. Each DHCP server requires a statically applied IP address.

DHCP was originally introduced in RFC 2131 back in March of 1997 (http://www.rfceditor.org/rfc/rfc2131.txt). Since the inception of DHCP, a number of add-on DHCP options have made it possible to disburse even more IP-related information to clients, making IP management much more flexible for IT administrators.

Source of Information : Syngress The Best Damn Windows Server 2008 Book Period 2nd Edition

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