• Use Default Client Preference Settings for DNS Dynamic Updates
  • Keep Audit Logging Enabled for Use in Troubleshooting
  • Prevent Undesired Forwarding and Relay of BOOTP and DHCP Message Traffic.
  • Use the Appropriate Ratio of Servers to Clients
  • Use 80/20 Scope Distribution Balance
  • Published: October 1, 2003

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    Integrate DHCP with Other Services

    Both WINS and DNS can register dynamic name-to-address mappings on a network. Operating DHCP with other name resolution services requires careful planning, and network administrators implementing DHCP should also develop a strategy for implementing DNS and WINS.

    Use Default Client Preference Settings for DNS Dynamic Updates

    DHCP in Windows Server 2003 can perform DNS dynamic updates for DHCP clients based on how clients request these updates. This setting provides the best use of the DHCP service to perform dynamic updates on behalf of its clients as follows:

    • DHCP client computers running Windows 2000, Windows XP, or a Windows server operating system explicitly request that the DHCP server update only pointer (PTR) resource records used in DNS for the reverse lookup and resolution of a client's IP address to its name. These clients update their address (A) resource records for themselves.

    • Clients running earlier versions of Windows cannot make an explicit request for DNS dynamic update protocol preference. When configured to do so, the DHCP Server service updates both the PTR and A resource records on behalf of the clients.

    Keep Audit Logging Enabled for Use in Troubleshooting

    By default, the DHCP Server service enables audit logging of service-related events. Audit logging provides a long-term service monitoring tool that makes limited use of server disk resources.

    Use Manual Backup and Restore

    Use the Backup command in the Action menu of the DHCP console to perform full backup of the DHCP service at an interval that helps protects you from significant data loss. The manual backup method includes all DHCP server data in the backup, including all scope information, log files, registry keys, and DHCP server configuration information (except DNS dynamic update credentials). Do not store these backups on the same hard drive on which the DHCP Server service resides, and make sure that the access control list (ACL) for the backup folder contains only the Administrators and DHCP Administrator groups as members.

    In addition to performing manual backups, back up to other locations, such as a tape drive, and make sure unauthorized persons do not have access to your backup copies. You can use the Windows Backup feature for this purpose. For more information, see “Best Practices for Backup” in the Windows 2003 Server Help and Support Center1.

    When restoring the DHCP service, you can use a backup created with either the Windows Backup feature or a copy of the database created with synchronous backup, which is available with the DHCP service. In addition, you can use the Restore command on the Action menu in the DHCP snap-in to restore a server running DHCP.

    Prevent Undesired Forwarding and Relay of BOOTP and DHCP Message Traffic.

    For routed networks, you can either use relay agents or set appropriate timers to prevent undesired forwarding and relay of BOOTP and DHCP message traffic. If you have multiple physical networks connected through routers, and you do not have a DHCP server on each network segment, the routers must be capable of relaying BOOTP and DHCP traffic. If you do not have such routers, you can set up the DHCP Relay Agent component on at least one server running Windows in each routed subnet. The relay agent sends DHCP and BOOTP message traffic among the DHCP-enabled clients on a local physical network and a remote DHCP server located on another physical network. When using relay agents, make sure to set the initial time delay in seconds so that relay agents wait before sending messages to remote servers.

    Use the Appropriate Ratio of Servers to Clients

    It is important to carefully determine how many DHCP servers are needed to serve all DHCP-enabled clients on a network. In a small LAN, such as one physical subnet without routers, a single DHCP server might serve all DHCP-enabled clients. However, routed networks might require several DHCP servers.

    Theoretically, there is no limit to the maximum number of clients that can be served by a single DHCP server; however, there are practical constraints based on the IP address class of a network and server configuration issues, such as disk capacity and CPU speed.

    Transmission speed between each segment for which DHCP service is provided is an important factor. With slower WAN links or dial-up links, a DHCP server is typically needed on both sides of these links to serve clients locally. Another factor is whether DHCP service is used in all or only selected physical networks. When deploying multiple DHCP servers for an environment, it is advisable to place them on different network segments for the case where a network segment becomes unreachable. DHCP Relay agents turn the broadcast into a unicast packet.

    Before installing the DHCP server, it is necessary to determine the following:

    • The hardware and storage requirements for the DHCP server.

    • The computers that can be configured immediately as DHCP clients for dynamic TCP/IP configuration and which must be manually configured with static TCP/IP configuration parameters, such as static IP addresses.

    • The DHCP option types and their values to be predefined for DHCP clients.

    • The DHCP Relay Agent configuration for your network.

    Use 80/20 Scope Distribution Balance

    You can split a scope between two or three servers so that a network can more easily handle DHCP traffic floods. In addition, stopped servers will not noticeably affect the network. An 80/20 split offers the optimum benefit.

    For example, consider a Class B scope with an address range from through and a subnet mask of You could set up two servers (SRV1 and SRV2) to distribute the load as follows:

    • SRV1 has a scope of through with a subnet mask of The exclusion range for this scope is through

    • SRV2 has a scope of through with a subnet mask of The exclusion range for this scope is through

    Similarly, you can divide a scope between three servers.
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