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This text assumes the reader will be using a computer (motherboard and BIOS) and NIC (network card) that are compatible with WoL technology and that the hardware is properly set up to do so. Some network cards must be placed into a special PCI slot on the motherboard in order work properly while others must be tethered to the motherboard by a special cable which plugs into a particular place on both the motherboard and the NIC. A general WoL FAQ can be located here. This text was written mainly to indicate how to forward the proper port through a Linksys router in order to utilize WoL technology through the router.
In order to use WoL (Wake on LAN, aka: RWU or remote wake up) to wake up a computer from over the Internet the appropriate port needs to be forwarded from the WAN side to the LAN side of the router. Since a computer that is not turned on doesn't have an IP address, the packet sent to wake the computer needs to be forwarded to all computers on the LAN side of the router in order to ensure it gets to the computer it is destined for. This "magic packet," which can be sent using software available from different sources, contains a special string designed to work with WoL as well as the MAC address of the network card in the computer which should wake up. Because the MAC address of the correct machine is included in the packet, only the machine that is supposed to wake up actually will.
To set up port forwarding in the router go here (default). The port that needs to be forwarded will vary depending on what software you're using to send the magic packet, but the normal port used for WoL is 9. UDP is the protocol that needs to be forwarded; it is not necessary to forward the TCP protocol. The IP address that the packet needs to be forwarded to will change depending on the network mask you are using on your LAN. The default network mask is 255.255.255.0. If you are using this mask, you should forward traffic destined to your WoL port to xxx.xxx.xxx.255. If you are using the default settings in the router, this address would probably be 192.168.1.255. The 255 in the address, using the default network mask, signifies that the router should forward any information sent to the indicated port to all computers on the LAN side. If you are using the router's default settings with a program that sends the "magic packet" to port 9, basically just forward all UDP traffic on port 9 to 192.168.1.255. If there is an option for external and internal ports, the same port number should be used for both external and internal.
WoL tool allows you to wake a computer remotely over the Internet through a browser. On this page they indicate UDP port 9 is what the tool uses, but as of this writing the magic packet is actually sent through UDP port 32767. So, if you're using this tool be sure to forward port 32767 through the router.
While it is possible to locate software that will send WoL "magic packets" via a quick search in your favorite search engine, a couple of sites offering such software are:
Depicus (also provides info on WoL)
AMD (also provides info on WoL)
This FAQ entry copied from the LinkSys FAQ and posted there by Gork
User svenlange adds that iptables (many routers are based on this) does not support forwarding to *.255 address - so the only option is direct forwarding to certain IP with permanent ARP entry.
See his thread on the subject: