Dynamic Host Configuration Protocol Life Cycle

To prevent an IP address from being indefinitely assigned to a client that has disconnected from the network, DHCP servers reclaim addresses at the end of the DHCP lease period. Halfway through a DHCP lease, the DHCP client submits a lease renewal request to the DHCP server. If the DHCP server is online, the DHCP server typically accepts the renewal, and the lease period restarts. If the DHCP server is not available, the DHCP client will try to renew the DHCP lease again after half the remaining lease period has passed. If the DHCP server is not available when 87.5% of the lease time has elapsed, the DHCP client will attempt to locate a new DHCP server and possibly acquire a different IP address.

If the DHCP client shuts down normally, or an administrator runs the command ipconfig /release, the client sends a DHCPRelease message to the DHCP server that assigned the IP address. The DHCP server then marks the IP address as available and can reassign it to a different DHCP client. If the DHCP client disconnects suddenly from the network and does not have the opportunity to send a DHCPRelease message, the DHCP server will not assign the IP address to a different client until the DHCP lease expires. For this reason, it’s important to use a shorter DHCP lease period (for example, 6 hours instead of 6 days) on networks where clients frequently connect and disconnect, such as wireless networks.