DHCP Improvements

In Windows 2000, DHCP's basic functionality remains unchanged from Windows NT 4.0, but Microsoft did introduce several new features. The DHCP Manager is now a Microsoft Management Console (MMC) snap-in, and it now offers better monitoring and statistical reporting capabilities. From the MMC DHCP Manager, right-click server_name and choose Show Statistics to access information such as the total number of addresses, how many addresses are available for lease requests or are in use, how long the server has been running, and more.

DHCP Authorization
Win2K DHCP servers that are members of an Active Directory (AD) domain or that run on a network that has an AD domain require authorization. Authorization is the process in which Win2K specifies which DHCP servers can assign IP address configuration information. Authorization prevents anyone from maliciously or accidentally installing a DHCP server on the network with an incorrect scope and scope options, which would disrupt network communications. To authorize a DHCP server, log on to the DHCP server with an account that's a member of the Enterprise Administrators group, open the MMC DHCP Manager snap-in, right-click server_name, and choose All Tasks, Authorize. When a DHCP server that's a member of an AD Domain boots up, it queries the AD to obtain a list of authorized servers, and the DHCP service will start only after it finds its IP address on the list. If the Win2K DHCP server is a member of a workgroup, it broadcasts an informational packet, DHCPINFORM, at startup, and all other DHCP servers on the segment should respond to that packet. If the workgroup member DHCP server receives a response from a DHCP server that's a member of an AD domain, the service won't start. If the workgroup member DHCP server receives responses only from other workgroup member DHCP servers or if it receives no responses, it won't let its DHCP service start and it will periodically send out DHCPINFORM broadcasts to verify that it's still operating as an authorized server.

DNS Integration
Another important update in Win2K DHCP is its integration with DNS. In a domain that includes NT 4.0 or Windows 9x machines that don't support dynamic DNS (DDNS), the DHCP server can register the clients' forward-lookup zone (A record) and reverse-lookup zone (PTR record). This support ensures that the DNS zone files contain records for all the hosts, not just the Win2K machines, on a network. Similarly, you can configure the DHCP server to register Win2K clients as well.

Class ID Options
In NT 4.0, all clients that receive an IP address from a particular DHCP scope receive the same scope options, including lease duration, default gateway, DNS server, and WINS server. In Win2K, you can specify that certain options are available to certain classes of clients. For example, you might want to set a class for mobile users so that you can specify that they use a shorter lease duration to make more efficient use of your available-address pool. When a client that requests IP configuration information from the DHCP server identifies itself as a member of the mobile users class, the DHCP server will issue that client a shorter lease than those that it issues to other DHCP clients. Before clients can identify themselves as members of a particular class, you must use the ipconfig.exe utility to configure each client. For example, you can issue the command

ipconfig/setclassid <local area connection> <mobile users> 

where <mobile users> corresponds to the class ID you configure on the DHCP server.

Multicast and BOOTP
Microsoft has added multicast address allocation and BOOTP support to Win2K DHCP. The DHCP server issues multicast addresses to applications that use multicast applications. The server issues these addresses from a multicast scope that you configure on the DHCP server using the new Scope wizard. Microsoft actually added BOOTP support to NT 4.0 DHCP in a service pack, and it enables RIS clients to receive an IP address when they boot up and contact the RIS server.

Many of Win2K DHCP's features are functionally similar to those in NT 4.0's version. However, Microsoft has added several useful features under the hood.

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