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Title: Wake on LAN mini HOWTO: Wake on LAN





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2. Wake on LAN



2.1 What is it?




The ability to switch on remote computers through special network
packets. This only works with network cards and motherboards that
are Wake on LAN compliant.

2.2 How does it work?




WOL is based on the following principle: 

When the PC shuts down, the NIC still gets power, and keeps listening on
the network for a 'magic' packet to arrive. This packet must contain a
certain byte-sequence, but can be encapsulated in any kind of packet
(IPX, IP, anything). Take a look at the code for the magic sequence.

This program uses UDP for sending the packet. The complete UDP packet, sent
over an ethernet interface, looks something like this:

[ethernet header][IP header][UDP header][Magic sequence][CRCS] 

The only goal of the script is to send this packet over the network. It
expects no returning data, since the NIC only listens, and does not reply
anything.

For a more detailed description of the protocol, see the AMD white paper.

2.3 Hardware requirements




Green PC, motherboard BIOS support,
network cards, PCI 2.2, 
Operating system support (Windows 95 - DELL's document -, 
Windows 98, Windows 2000)



Motherboards



Most modern ATX motherboards should have a 3-pin Wake-on-LAN connector
near the PCI slots and should included BIOS support for Wake-on-LAN
power up. If you have an Award BIOS check the Power Management
Setup for this option.

Network cards



The network card should also include a 3-pin Wake-on-LAN connector.
One of the network cards that includes this connector is the
Intel Pro/100+ (chipset 82559)

2.4 Wake-up frame




A Wake-up frame is a special data packet containing the Ethernet
address of the remote network card. Somewhere in this frame
should exist a byte stream (magic sequence) composed by, at the
least, 16 times the repetition of the Ethernet address
and preceded by a synchronization stream of 6 bytes of FFh.

Magic sequence



If the Ethernet address of a target computer is 01:02:03:04:05:06
(6 bytes), then the LAN controller of that machine should
be looking for the following sequence

    FFFFFFFFFFFF010203040506010203040506010203040506010203040506
    010203040506010203040506010203040506010203040506010203040506
    010203040506010203040506010203040506010203040506010203040506
    010203040506010203040506



inside the frame.

IEEE address



Make reference to O'Reilly book about Ethernet and his author homepage.


IEEE
TCP/IP broadcast addresses





        Internetworking with TCP/IP
        Volume I: Principles, protocols, and architecture (third edition)
        Douglas E. Comer
        Prentice Hall



Make reference to chapter 4 of this book. Chapter 4 describes Internet address
(see sections 4.5, 4.6 e 4.11).


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