Enhanced monitoring and statistical reporting provides notification when the number of available IP addresses falls below a 90 percent threshold. To alert network managers, icon color, which is associated with the remaining addresses falling below the defined level, changes to yellow. The icon color changes to red whenever the addresses become completely depleted.
The DHCP snap-in, which supports Simple Network Management Protocol (SNMP) and Management Information Bases (MIBs) for DHCP statistics, provides the graphical display of statistical data. This interface helps administrators monitor system status, such as the number of available addresses versus depleted addresses, or the number of leases processed per second. Additional statistical information includes the number of messages and offers processed, as well as the number of requests, acknowledgements (DHCPACKS), declines, negative status acknowledgment messages (DHCPNACKS), and releases received.
The DHCP snap-in can display the total number of scopes and addresses on a server, the number used, and the number available for a particular scope.
DHCP Vendor-Specific and Class ID Option Support
In Windows Server 2003, DHCP supports vendor-specific defining of options. When an option is identified as vendor-specific, DHCP looks up the configuration as specified for the specific vendor. This feature enables the quick introduction of compelling custom applications for enterprise networks. Equipment from multiple vendors on a network can also use different option numbers for different functions. RFC 2132 describes the vendor class and vendor options.
Most implementations of DHCP treat clients equally, rendering the server unaware of the specific types of clients with which it interacts. This behavior necessitates a common configuration issued by the server to all DHCP clients. It also restricts the server to assigning only an address from a scope, along with the options available within that scope.
In Windows Server 2003, the implementation of user classes allows DHCP clients to distinguish themselves by specifying a client type, such as a desktop or laptop. An administrator can then configure a DHCP server to assign different options, depending on the type of client receiving them. For example, the server could assign short leases to laptop clients, while desktop clients on the same network might require other settings. User class support gives administrators greater flexibility in configuring clients.
Vendor and user classes are made available for use by DHCP clients and servers in a variety of ways. The following table compares and contrasts the features of these classes.
Part of proposed DHCP standard drafts. For updated information, obtain the latest draft from the Request for Comments Web site at http://ietf.org/.
Part of accepted DHCP standard drafts (RFC 2131, 2132).
Clients identify user class membership with user class information.
Clients identify vendor class membership by using the vendor class identifier option.
User class IDs can be set and viewed at DHCP clients running Windows 2000, Windows XP, or Windows Server 2003 operating systems by using the ipconfig command.
Vendor class IDs are configured internally by DHCP client system vendors, such as Microsoft and other vendors.
When adding a vendor class at the server, you need to specify class data at the server that exactly matches the class ID used by same-vendor clients. For more information, contact the applicable vendor.
With user classes, you can take advantage of predefined classes that can be used to support specialized groups of clients, such as Bootstrap Protocol (BOOTP) or Routing and Remote Access clients.
Vendor classes provide classification of DHCP clients by Windows 98, Windows 2000, or Microsoft DHCP clients, which share the use of the Microsoft-reserved vendor prefix (MSFT) in any class-related data.
User classes are typically created for administrative reasons, such as to identify all DHCP clients in a specific site or location. For example, all computers and printers located on the same floor in an office building might be assigned or configured as part of the same user class.
Vendor classes are typically created for the enhancement of vendor-specific DHCP functionality. For example, Microsoft provides several additional vendor-specific options, such as the ability to disable NetBIOS over TCP/IP for DHCP clients running Windows 2000 or Windows XP.
User classes are most helpful to users for managing DHCP option assignments based on their needs. If your DHCP network is large enough to benefit from user classes, you can freely customize your DHCP environments with them. In most cases, the user class provides a way to assign and override standard DHCP option values set at either the server, scope, or reserved client level.
Vendor classes are most helpful to vendors for managing DHCP option assignments based on vendor-specific needs without disturbing other non-vendor DHCP clients. With a vendor class, options are passed to clients using the vendor specific information option, which encapsulates the options it sends. This behavior helps non-vendor clients to recognize the information as vendor-specific so they can ignore and discard it as needed.