Determining How Many DHCP Servers to Deploy

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

A single DHCP server can serve an almost unlimited number of clients. However, factors such as the size and layout of your network, the IP address class selected for use, and the volume of traffic on your network often make this impractical. You can deploy multiple DHCP servers to reduce the volume of DHCP-related traffic across your network and create faster response times for DHCP messages. Deploying multiple DHCP servers also creates fault tolerance on your network. If you choose to deploy more than one DHCP server, it is important to weigh the benefits of increased response times against the costs required for additional hardware.

When deciding how many DHCP servers you need, consider:

  • The location of DHCP-enabled clients on your network.

  • The transmission speeds between the segments for which DHCP service is provided.

    If you have slower WAN or dial-up links, place a DHCP server on both sides of these links to improve DHCP response times for local clients.

  • The network traffic that DHCP produces, as well as your current network traffic.

    If your current volume of network traffic is high, consider deploying multiple DHCP servers to reduce the volume of DHCP requests traveling across the network. Make sure to account for periods when network traffic is heaviest, such as the beginning of the day, when many users turn on their computers at the same time.

  • Disk space requirements.

    It is important to consider the database size when choosing your hardware. Each lease requires approximately 600 bytes per lease for the database, plus 1200 bytes for backup (600 bytes for the backup and 600 bytes for the temporary directory). In addition, the audit logs require approximately 500 bytes per lease transaction and are stored for seven days.

    Tip

    • In general, allow at least 50-70 MB for the audit logs, however the number of lease transactions depends on the number of leases as well as the lease duration.

    To figure out how much hard disk space is required, first multiply the number of leases by 600 bytes, then multiply the estimated number of lease transactions by 500 bytes, and add these two results. The sum is the minimum amount of disk space required by the DHCP server.

    For example, a DHCP server with 10,000 leases and lease duration of one week requires approximately 18 MB to store the leases and the backup (6 MB for the database, 6 MB for the backup, and 6 MB for the temporary database). The audit logs would require an absolute minimum of 10 MB: 5 MB (500 bytes x 10,000 leases) for startup, and 5 MB when the leases renew halfway through the week. If the number of leases increases or if lease time is shortened, this requirement will increase. A company might allocate 100 MB for audit logs to allow for flexibility in adding leases or reducing lease duration, as well as dealing with any peak-load events.