DHCP Address Assignment
n If an address is available, the new address SHOULD be
chosen as follows:
The client's current address as recorded in the client's current
binding, ELSE
The client's previous address as recorded in the client's (now
expired or released) binding, if that address is in the server's pool
of available addresses and not already allocated, ELSE
The address requested in the 'Requested IP Address' option, if that
address is valid and not already allocated, ELSE
A new address allocated from the server's pool of available
addresses; the address is selected based on the subnet from which
the message was received (if 'giaddr' is 0) or on the address of the
relay agent that forwarded the message ('giaddr' when not 0).