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Wake-On-LAN Tool

 
   

Objectives

"Wake-On-LAN" is AMD's term for a cross-network power-on capability that is supported on their newer Ethernet cards, with certain motherboards. It allows a PC to be nominally turned off and to be turned on automatically for a scheduled management procedure, e.g. in the middle of the night. AMD have coined the term "Magic Packet" to describe the special network packet that can be sent to sleeping network cards to wake them up. Intel also support a similar feature with some of their cards/motherboards ("Wired for
  Management" is their term). Intel's network packet is a slightly different format.
In terms of the project, it was necessary to design a 32-bit application for MS Windows 9x/Me/NT4/2k/XP/2003 without GUI that would provide functionalities to:

detect if a PC, that has the network interface with the specified IP-address, is turned on;

detect the MAC-address of the network interface corresponding to the specified IP-address;

wake a PC up remotely.
   

Results

The application is developed to be included into the network management suite. It was assumed that the application would mainly be used for remote PC wake-up by the schedule in order to perform the hardware and software inventory operations and remotely install the software. To form the "Magic Packet",
  it is necessary to know the MAC-address of the network interface. It is assumed that the utility will allow to detect if the OS core of the PC, that has the network interface with the specified IP-address, is loaded. If it is, then the utility should get and save the MAC-address for the following PC Wake-On-LAN.
   

Developer's comments


Q: How does this work?

KB_Soft: Let's examine every function individually. To detect if the PC, that has the network interface with the specified IP-address, is turned on, the application generates the UDP-datagram that contains the echo message (a ping message) in its ICMP (Internet Control Message Protocol) packet. One of the complicated moments was to get the MAC-address of the remote network interface by its IP-address. For this task, a simple but effective solution was found. The application sends the echo message to the specified IP-address. Then, if the reply follows, it extracts the target MAC-address from the ARP table of the local PC. It is assumed that the target machine is located in the same subnetwork and, therefore, in order to send an IP-packet to the target PC, the system will execute the ARP request and put the MAC-address
  of the specified network interface into the ARP table. Now let us pass on to the issue of the Wake-On-LAN. It is rather simple.

The MAC-address is being extracted by the specified IP-address (the MAC-address is being searched among the saved ones). Later on, the "Magic Packet" is being formed and sent to the network in the form of a broadcast datagram.

Q: What was the most complicated issue in this project?

KB_Soft: Well, the most complicated task was to implement the function getting the MAC-address of the remote network interface. We had the strictly limited period of time to implement the project. We examined several versions of its implementation, which resulted in the simplest and most effective solution.