DHCP Lease Renewal and Rebinding Processes
(Page 1 of 3)
Once a DHCP client completes the allocation or reallocation process, it enters the BOUND state. The client is now in its regular operating mode, with a valid IP address and other configuration parameters it received from the DHCP server, and can be used like any regular TCP/IP host.
While the client is in the BOUND state, DHCP essentially lies dormant. As long as the client stays on and functioning normally, no real DHCP activity will occur while in this state. The most common occurrence that causes DHCP to wake up and come active again is arrival of the time when the lease is to be renewed. Renewal ensures that a lease is perpetuated so it can be used for a prolonged period of time, and involves its own message exchange procedure. (The other way that a client can leave the BOUND state is when it terminates the lease early.)
If DHCP's automatic allocation is used, or if dynamic allocation is used with an infinite lease period, the client's lease will never expire, so it never needs to be renewed. Short of early termination, the device will remain in the BOUND state forever, or at least until it is rebooted. However, as we've already discussed, most leases are finite in nature. A client must take action to ensure that its lease is extended and normal operation continues.
To manage the lease extension process, two timers are set at the time that a lease is allocated. The renewal timer (T1) goes off to tell the client it is time to try to renew the lease with the server that initially granted it. The rebinding timer (T2) goes off if the client is not successful in renewing with that server, and tells it to try any server to have the lease extended. If the lease is renewed or rebound, the client goes back to normal operation. If it cannot be rebound, it will expire and the client will need to seek a new lease.
Home - Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.