Changing the Addressing of a Subnet

In the course of DHCP administration, you might find it necessary to modify or completely change a subnet's addressing.

If you merely need to modify the range of a current scope, you can achieve this task by changing the address range or exclusion ranges of the subnet's defined DHCP scope.

Important Change scope properties with care so as not to exclude active leases, and so as not to include within the reconfigured scope any addresses on the subnet that have been manually assigned to other computers.

If you need to migrate to a completely new scope, however, you must first add a new scope to the DHCP server and then migrate to that new scope. To perform such a migration, first create and activate the new scope, and then deactivate the old scope. Do not delete the deactivated scope until the clients have migrated to the new scope. To migrate clients, either wait for the clients to automatically renew their leases (after 50 percent of the configured scope lease time has elapsed) or manually renew clients by executing the Ipconfig /release command followed by the Ipconfig /renew command on the client computers. Once all clients have been moved or forced to seek leases in another scope, you can safely delete the inactive scope.

Tip You can enable conflict detection on the Advanced tab of the DHCP server properties dialog box. This feature allows you to specify the number of times the DHCP server will ping a given address on the network before assigning that address to a client. If the ping receives a reply, the address will not be assigned. This feature is useful, for example, if you need to deploy a new DHCP server to replace one that has recently failed. In this case, without the aid of an up-to-date DHCP server database, conflict detection can ensure that currently active leases are not assigned to other clients.