[cisco-voip] IP phone conflicts in DHCP after power failed!

[George Dormishev]

It's very strange how ip phone cannot get ip address or get dhcp conflicts 
with dhcp server when they get power failed  with the switch who acts like 
dhcp server .Not all the phones get this kind of long registering after power 
failed but most of them do.Any ideas why the switch dchp database do contain 
an old ip addresses from which phones get conflicted after they try to get an 
address from the dhcp on the switch???