Network Administration: Scope Exclusions
In the case of Dynamic Host Configuration Protocol (DHCP) scopes, exclusions can help you to prevent IP address conflicts and can enable you to divide the DHCP workload for a single subnet among two or more DHCP servers.
An exclusion is a range of addresses that are not included in a scope. The exclusion range falls within the range of the scope’s starting and ending addresses. In effect, an exclusion range lets you punch a hole in a scope. The IP addresses that fall within the hole won’t be assigned.
Here are a few reasons for excluding IP addresses from a scope:
The computer that runs the DHCP service itself must usually have a static IP address assignment. As a result, the address of the DHCP server should be listed as an exclusion.
Some hosts may not be able to support DHCP. In that case, the host will require a static IP address. For example, you may have a really old MS-DOS computer that doesn’t have a DHCP client. By excluding its IP address from the scope, you can prevent that address from being assigned to any other host on the network.