7004716: Understanding and Troubleshooting ZCM’s role in WOL

ZCM’s role in WOL is for the Server to generate and transmit an industry standard WOL packet.
Once the packet is created and transmitted, it is up to the network devices to deliver the packet to the target workstation.
The target workstation must then accept and respond to the WOL packet.
The ZCM Agent does not play any role in responding to the WOL packet.

ZCM stores each device’s last known IP address and Subnet mask and uses that to send a WOL packet to the broadcast address of that computer’s subnet.
For Class “C” Network such as 192.168.1 with the default 255.255.255 subnet mask, the Broadcast address would be 192.168.1.255.
To determine the broadcast address of other Class Networks with other subnet masks, you can use a “Subnet Calculator” to determine the proper broadcast subnet.
An example of such a resource is the following: http://www.subnet-calculator.com/.

The WOL Packet itself will contain the MAC address of the target device repeated 16 times.
An actual WOL packet is displayed below:
Key parts of the packet to note are the following:
Destination: 192.168.1.255 which is the broadcast address for the device’s subnet.
Protocal: WOL. Ethereal identifies the packet as a WOL packet which helps indicate the packet is properly formed.
Packet Contents: The MAC address of the device is repeated precisely 16 times.
Along with using a packet capture tool to verify what is actually hitting the wire, you can enable debug logging on your ZCM server.
The loader-messages.log file will contain the details about the WOL packet activity.
A snippet of the logs will clearly show what it believes to be the IP address, SubnetMask, and MACAddress of the target device.
This should correspond to the actual packet that is transmitted above.
———————————————————————————————————–
[DEBUG] [10/21/09 2:07:38 PM] [] [WakeOnLANHandler : Sending packet for retry count : 0]
[DEBUG] [10/21/09 2:07:38 PM] [] [IPaddress = 192.168.1.77 SubnetMask = 255.255.255.0MACAddress = 000c29e960d1]
Currently there are not any known issues where the incorrect information is used to generate a WOL packet or the WOL packet is not generated properly.
When reporting any WOL issues to Novell, please be sure to include both the log file and packet capture and indicate whether the logs shows the wrong information being supplied to generate the WOL packet or the capture demonstrating the WOL packet does not match the information that was supplied.

Related:

Leave a Reply