How to Configure Dynamic Host Configuration Protocol Servers with Split Scopes

This article describes how to configure Dynamic Host Configuration Protocol (DHCP) servers with split scopes.

You can implement split scopes, create identical scopes, and exclude opposite portions of the address range on each DHCP server. For example, assume that there are two DHCP servers: DHCPServerA and DHCPServerB. Both servers serve the 192.168.1.0 subnet, where the host addresses is between 192.168.1.1 and 192.168.1.254. In this example, the scope is split in half.

On DHCPServerA, create a scope with a start address of 192.168.1.1 and an end address of 192.168.1.254, and then create an exclusion from 192.168.1.127 to 192.168.1.254.

On DHCPServerB create the same scope: the start address 192.168.1.1 and the end address 192.168.1.254. Then, create an exclusion from 192.168.1.1 to 192.168.1.126.

A scope can also be divided between more than two servers in a similar way using the preceding guidelines.

If you create two Microsoft (MS) DHCP servers with the same scope without any exclusions, you can cause each DHCP server to send a NACK request from the opposite DHCP server. This configuration may result in clients that are unable to obtain leases, or clients that take very long periods of time to obtain leases.

You can confirm this behavior by examining Event Viewer for event 1011. Also, the DHCP Audit log lists any corresponding DHCPNACK entries.

NOTE: Incorrectly configured split scopes are only one possible cause of a DHCPNACK message.