Where should DHCPNAK be sent to as lease expiration notice when Relay Agent Info option is in use?

[michael kapelko]

Hi.
As you may know I'm writing own small DHCP server.
I wonder where should DHCPNAK about lease expiration be sent to - to
'ciaddr' at 68th port or to 'giaddr' to 67th port. I tried to
artificially decrease lease time and tried both addresses, but Windows
XP didn't catch them, even though 'windump' showed packets coming.
Is client not required to notice lease expiration NAK messages? Or am
I doing anything wrong?
Thanks.