DHCP renew process
Definition: The DHCP lease renewal process is the process by which the DHCP client renews or updates its IP address configuration data with the DHCP server.
Purpose of the DHCP Lease renewal process
The DHCP client renews its IP configuration data prior to the expiration of the lease time. If the lease period expires and the DHCP client has not yet renewed its IP configuration data, the DHCP client loses the IP configuration data and begins the DHCP lease generation process again.
The lease renewal process is the result of the lease period value. The lease period value ensures that DHCP maintains the IP address information and that clients regularly update or renew their IP address configuration data. Having DHCP maintain this information means that you can manage IP addressing for the DHCP server.
At any time during the lease period, the DHCP client can send a DHCP RELEASE packet to the DHCP server to release the IP address configuration data and to cancel any remaining lease.
Automatic lease renewal process
The client must renew its IP configuration data before the lease period expires. A DHCP client automatically attempts to renew its lease as soon as 50 percent of the lease duration has expired. The DHCP client also attempts to renew its IP address lease each time that the computer restarts. To attempt a lease renewal, the DHCP client sends a DHCP REQUEST packet directly to the DHCP server from which the client obtained the lease.
If the DHCP server is available, it renews the lease and sends the client a DHCP PACK packet that includes the new lease duration and any updated configuration parameters. The client updates its configuration when it receives the acknowledgment. If the DHCP server is unavailable, the client continues to use its current configuration parameters.
If the DHCP client fails to renew its lease the first time, the DHCP client broadcasts a DHCP DISCOVER packet to update its address lease when 87.5 percent of the current lease duration expires. At this stage, the DHCP client accepts a lease that any DHCP server has issued.
Note : If a client request an invalid of duplicate address for the network, a DHCP server can respond with a DHCP denial message (DHCP NAK packet). This forces the client to release its IP address and obtain a new, valid address.
Manual lease renewal:
You can renew an IP lease manually if you need to update DHCP configuration information immediately. (For example, if you want DHCP clients to immediately obtain the address of a newly installed router from a DHCP server, renew the lease from the client to update its information.)