Updated: January 21, 2005
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
IP addresses are leased by the DHCP server to its clients. Each lease has an expiration date, which the client must renew if it is going to continue to use that address.
Leases are retained in the DHCP server database four hours after expiration. This grace period protects a client lease in case the client and server are in different time zones, the individual computer clocks are not synchronized, or the client computer is off the network when the lease expires. Expired leases are included in the list of active leases and are distinguished by a different icon.
You can delete the lease of any DHCP client in the scope. The main reason for doing so is to remove a lease that conflicts with an IP address exclusion or a client reservation that you want to add. Deleting a lease has the same effect as if the client lease expired: the next time that client computer starts, it must enter the initialization state and obtain new TCP/IP configuration information from a DHCP server. There is nothing, however, to prevent the client from obtaining a new lease for the same IP address. You must make the address unavailable before the client requests another lease.
Delete only entries for clients that are no longer using the assigned DHCP lease or that are to be moved immediately to a new address. Deleting an active client could result in duplicate IP addresses on the network, because deleted addresses will be assigned to new active clients. After you delete the lease of the client and set a reservation or exclusion, you should always use ipconfig /release on the client computer to force the client to free its IP address.
You can view lease information for individual clients by first selecting the Active Leases folder for a scope in the DHCP console. When Active Leases for a scope is selected as the console view, the list of currently active client leases for the scope appears in the details pane.
Modifying default lease durations for a scope
When a scope is created, the default lease duration is set to eight days. In most cases, this value is sufficient. However, because lease renewal is an ongoing process that can affect the performance of DHCP clients and your network, it is sometimes useful to change the lease duration. Use the following guidelines to decide how to best modify lease duration settings for improving DHCP performance on your network:
If you have a large number of IP addresses available and configurations that rarely change on your network, increase the lease duration to reduce the frequency of lease renewal queries between clients and the DHCP server. This reduces some network traffic caused by clients renewing their leases.
If you have a limited number of IP addresses available and if client configurations change or clients move often on your network, reduce the lease duration to promote scavenging of old IP addresses by the DHCP server. This increases the rate at which addresses are returned to the available address pool for reassignment to new clients.
You can also set a separate lease time, different from the default scope lease time used by your DHCP clients, such as alternate lease times for supporting other types of clients such as BOOTP or Routing and Remote Access clients. For more information, see Manage BOOTP and Remote Access Clients.