Determining Lease Duration
Updated: March 28, 2003
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
When a scope is created, the default lease duration is set to eight days. However, because lease renewal is an ongoing process that can affect the performance of DHCP clients and your network, you can increase or decrease the lease duration to fit your specific needs. Determine what segments of your network have specific lease duration requirements, and decide how best to modify lease duration settings to improve DHCP performance on your network.
You can set the lease duration in the Lease Duration page of the New Scope Wizard. For more information about using the New Scope Wizard, see "Creating Scopes" earlier in this chapter.
To set the lease duration after a scope is created
In the DHCP snap-in, select and right-click the scope you want to configure.
In the Lease duration for DHCP clients box, adjust the lease time for the scope.
Increasing the Default Lease Duration
You can increase the lease duration in a scope to reduce network traffic. Increase the lease duration only if that segment of your network has a large number of IP addresses available and a configuration that rarely changes. Increasing lease duration reduces the rate at which IP addresses are reclaimed when changes occur.
In a more stable environment, you can use a long lease, such as several months. This ensures both that addresses are ultimately recovered, and that DHCP-related network traffic is kept to a minimum.
Use caution when configuring unlimited lease durations. Even stable environments have a certain amount of client turnover. At a minimum, roving computers might be added and removed, desktop computers might be moved from one office to another, and network adapters might be replaced. If a client with an infinite lease is removed from the network, the DHCP server is not notified, and the IP address cannot be reused.
Reducing the Default Lease Duration
Reduce the lease duration for segments of your network that have any of the following:
A limited number of IP addresses available.
Client configurations that change frequently.
Clients that relocate often; for example, because they connect to conference rooms or wireless networks.
Although reducing the lease duration creates more DHCP-related network traffic, it increases the rate at which addresses are returned to the available address pool for reassignment. With an average volume of DHCP request traffic, Windows Server 2003 DHCP has a four-hour default grace period after which an expired lease can be reused. This means that an address is marked for deletion four hours after the lease expires, regardless of lease duration. When the volume of DHCP-related traffic is heavy and no leases are available to service lease requests, DHCP immediately instantiates a cleanup cycle, which reclaims any leases marked for deletion. By default, the cleanup cycle occurs every 60 minutes. You can adjust the duration of the default grace period after which an expired lease is marked for deletion by editing the following key in the registry:
Do not edit the registry unless you have no alternative. The registry editor bypasses standard safeguards, allowing settings that can damage your system, or even require you to reinstall Windows. If you must edit the registry, back it up first.