You will probably decide to install more than one DHCP server, so the failure of any individual server will not prevent DHCP clients from starting. However, DHCP does not provide a way for DHCP servers to cooperate in ensuring that assigned addresses are unique. Therefore, you must divide the available address pool among the DHCP servers to prevent duplicate address assignment.
A typical scenario is a local DHCP server that maintains TCP/IP configuration information for two subnets. For each DHCP server, the network administrator allocates 70 percent of the IP address pool for local clients and 30 percent for clients from the remote subnet, and then configures a relay agent to deliver requests between the subnets.
This scenario allows the local DHCP server to respond to requests from local DHCP clients most of the time. The remote DHCP server will assign addresses to clients on the other subnet only when the local server is not available or is out of addresses. This same method of partitioning among subnets can be used in a multiple subnet scenario to ensure the availability of a responding server when a DHCP client requests configuration information.