New DHCP server cause IP Phones to reboot

K_require · ‎07-17-2008

All of our IP Phones are DHCP enabled. Today we setup the DHCP server in our environment and moved the DHCP scope i.e range of IP addresses from old server onto the new one. All IP phones automatically got registered to this new DHCP server. My question is if these IP Phones were properly up and working fine, they already had got the IP addresses then how all IP Phones got rebooted and got registered to new server?

ivillegas · ‎07-23-2008

If an IP phone could not renew its lease at half lease time, it would keep on trying periodically until the lease's end. At that point, it surrenders its IP address, and is not usable as a phone until the DCHP server comes back.

But, while the lease has not yet expired, if the phone is powered off and on again, it will boot up without being able to get a DHCP server's acknowledgment to the phone's DHCP request. The phone would then assume the last known good DHCP scope, and not start the lease timer until a DHCP server was heard from. In other words, it would come back up and stay up forever if no DHCP server were to appear.