Determining Network Connectivity Strategies
Determining Network Connectivity Strategies |
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The new features of Windows 2000 DHCP allow for a more flexible and extensible way to assign IP addresses to hosts. These new features are described in the following sections.
The general status of DHCP servers, scopes, and clients, or "member items," can be graphically tracked by the use of icons displayed in the DHCP Manager. For more information about this subject, see the DHCP Manager online Help.
An extension to the Windows 2000 DHCP protocol standard supports the assignment of IP multicast addresses that are distributed in the same manner as unicast addresses. In Multicast DHCP, multicast scopes are configured in the same manner as regular DHCP scopes, but instead of using Class A, B, or C addresses, Class D scope uses a range of 224.0.0.0 to 239.255.255.255.
Typical applications for multicast are video and audio conferencing, which usually require users to specially configure multicast addresses. Unlike IP broadcasts, which need to be readable by all computers on the network, a multicast address is a group of computers that uses group membership to identify who receives the message.
The multicast address allocation feature has two parts: the server side, which hands out multicast addresses; and the client side application programming interface (API), which requests, renews, and releases multicast addresses. To use this feature, you need to first configure the multicast scopes and the corresponding multicast IP ranges on the server through the DHCP snap-in. The multicast addresses are then managed like normal IP addresses, and the client can call the APIs to request a multicast address from a scope.
Domain Name Servers provide name resolution for network resources and are closely related to DHCP services. In Windows 2000, DHCP servers and clients can register with Windows 2000 DNS dynamic update protocol. The integration of DHCP and DNS enables the registration of both type A (name-to-address) and Pointer (PTR) or address-to-name records. This allows the DHCP server to act as a proxy on behalf of Windows 95 and Windows NT 4.0 Workstation clients for the purpose of dynamic update registration within Active Directory.
When using DHCP and DNS together on your network, consider whether or not you have older, static DNS servers in use. Static DNS servers cannot interact dynamically with DHCP and keep name-to-address mapping information synchronized in cases where DHCP client configurations change, such as with a mobile user who is always moving from subnet to subnet within an intranetwork. In this situation, it is best for you to upgrade all static DNS servers to Windows 2000 DNS.
The DHCP service for Windows 2000 is designed to prevent unauthorized DHCP servers from creating address assignment conflicts. This solves problems that might otherwise occur if users created unauthorized DHCP servers that could assign invalid IP addresses to clients elsewhere on the network. For example, a user could create what was intended to be a local DHCP server by using addresses that are not unique, which could lease the addresses to unintended clients requesting addresses from elsewhere on the network.
The DHCP server for Windows 2000 has management features to prevent unauthorized deployments and to detect existing unauthorized DHCP servers. In the past, anyone could create a DHCP server on a network, but now an authorization step is required. Authorized personnel usually include the administrator of the domain that the Windows 2000 Server platform belongs to or someone to whom they have delegated the task of managing the DHCP servers.
DHCP servers respond to both bootstrap protocol (BOOTP) requests and DHCP requests. BOOTP is an established TCP/IP standard [RFC 951] for host configuration that precedes DHCP. BOOTP was originally designed to enable boot configuration for diskless workstations. These workstations have a limited ability to store and locally retrieve IP addresses, and other configurable information that you need during the boot process to join a TCP/IP-based network.
With the new support for dynamic BOOTP, a pool of addresses can be designated for BOOTP clients in the same manner in which a scope is used for DHCP clients. This allows IP addresses to be dynamically managed for distribution to BOOTP clients. This also allows the DHCP service to reclaim IP addresses used in the dynamic BOOTP address pool, after first verifying that a specified lease time has elapsed and that each address is still in use by the BOOTP client.
This feature provides a special-purpose local users group, the DHCP Users group, that is added when you install the DHCP service. By using the DHCP Manager console to add members to this group, you can provide read-only access to information related to DHCP services on a server computer for nonadministrators. This allows a user who has membership in this local group to view, but not modify, information and properties stored at a specified DHCP server. This feature is useful to Help desks when they need to pull DHCP status reports. Read/write access can only be granted though membership in the DHCP Administrators group.