Wake on local area network (LAN) functionality is provided in a multi-root environment. An I/O device, which is share by a plurality of physical hosts, receives the MAC address contained in the wake up packet, then prepares and sends an appropriate wake signal to the targeted host. In one embodiment, the shared I/O device sends an out-of-band wake up signal to each of the physical host computers, wherein the wake up signal is a serial bit stream encoded with the MAC address so that only the physical host having a MAC address matching the MAC address in the wake up signal will be turned on. In another embodiment, the shared I/O device sends a binary ON/OFF signal directly to the targeted physical host computer over a signal line associated with the MAC address.