>>bigthy+(OP)
Neither really, though my ISP's router would allow me to assign IPs by MAC address so they're effectively reserved to a device. The router's web UI displayed a list of devices. I wanted to see if devices would start dropping off this list as soon as the DHCP lease time expired. When they did drop off this list, I had thought they reappeared with the same IP without me explicitly using the reservation functionality. So how was this happening? I figured the web UI might not be showing the full picture of all the data about devices; that the router held records of formerly connected devices beyond the DHCP lease time for some unknown reason.