Managing Lease Durations

When a scope is created, the default lease duration is set to eight days, which works well in most cases. However, because lease renewal is an ongoing process that can affect the performance of DHCP clients and your network, it might be useful to change the lease duration. Use the following guidelines to decide how best to 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 network traffic.

  • If there are a limited number of IP addresses available and if client configurations change frequently or clients move often on the network, reduce the lease duration. This increases the rate at which addresses are returned to the available address pool for reassignment.

  • Consider the ratio between connected computers and available IP addresses. For example, if there are 40 systems sharing a Class C address (with 254 available addresses), the demand for reusing addresses is low. A long lease time, such as two months, would be appropriate in such a situation. However, if 230 computers share the same address pool, demand for available addresses is greater, and a lease time of a few days or weeks is more appropriate.

  • Use infinite lease durations with caution. Even in a relatively stable environment, there is a certain amount of turnover among clients. At a minimum, roving computers might be added and removed, desktop computers might be moved from one office to another, and network adapter cards 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. A better option is a very long lease duration, such as six months. This ensures that addresses are ultimately recovered.