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Appendix 3-4 Wake On LAN Rev.A
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Network Wake-Up Frames
This method does not require a special data pattern, unlike Magic Packet. If this mode is
enabled, a Wake Up request is issued when a special frame is detected within communication
frames.
Wake Up frames are of the following types:
❏
ARP request
Ethernet makes use of MAC (media access control) addresses, so the MAC address must be
determined in some way. This is handled by ARP (address resolution protocol). When a packet
is sent via IP, it is essential to determine what the MAC address of the network destination is,
which is achieved by broadcasting an ARP packet including the destination IP address. The
machine with the specified IP address returns its MAC address to the originating machine. To
increase packet transmission speed and reduce the number of broadcast requests to be checked
by networked machines, each machine is provided with an ARP cache. Each time an ARP
request is sent and a response received, an entry is made in the machine internal ARP cache
showing the correspondence between IP address and MAC address. When the machine issues
an IP packet, it first searches for that IP address in its internal cache, and uses the MAC address
if found there. If it is not found, it broadcasts an ARP request.
❏
NetBIOS name search
The NetBIOS name is the computer name, user name or domain name assigned to the
machine (a name with a unique 16th byte). When network services are used, the IP address
assigned to this NetBIOS name must be known. The most common way to determine the IP
address from the NetBIOS address is to broadcast a packet including the target NetBIOS
name. The corresponding computer receives the packet and it will respond, then resolve the
IP address.
Again, the correspondence between the NetBIOS name and IP address is stored in the
machine internal ARP cache.
❏
IP frames sent to machines
These frames use the IP protocol, and are sent directly to the correct MAC address.
These packets may be sent at Windows boot, at NT log-on, and at shutdown for other OS. The
ARP packets are used to determine the correspondence between IP and MAC addresses, but
may wake up a machine unintentionally during network allocations, or if a machine has been
communicated with previously.