Wake-On-LAN / Cisco Mac address-tables
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Recently I scheduled my computers to power on using Wake-On-LAN. There seems to be an issue with some of the computers not turning on. All the computers have identical hardware and have the same BIOS settings.
I did some investigation and I noticed that the computers that were not turning on did not have their MAC addresses listed in the switches. If I power the computer on long enough for the switch to add the computer's MAC and then power it off, wake-on-LAN will work.
I think there is an issue with the switches deleting the MAC adresses out of it's table? After some research I found the Cisco switches hold this data for 300 seconds (5min) then delete it.
I do not want to statically set all the MAC addresses in the switches if I do not have to. I have heard you can extend this deletion time, but it is not reccomended and this would be a troublesome when moving computers around.
Am I missing something? Anyone else using wake-on-LAN? Thanks for the help!
Software/Hardware used:
Software/Hardware used:
ASKED:
January 5, 2007 12:16 PM
UPDATED:
January 17, 2007 3:57 PM
Answer Wiki:
Have you set the NIC property to use the Magic Packet Frame? This worked for me.
Once the LAN controller has been put into the Magic Packet mode, it scans all incoming frames addressed to the node for a specific data sequence, which indicates to the controller that this is a Magic Packet frame.
To see all answers submitted to the Answer Wiki: View Answer History.
eDuTek,
How would the magic packet find it’s way to the correct port on the switch if it is not listed in the switch’s MAC address table? As far as I know, the MAC addresses are learned dynamically and this can only happen whtn the computer is powered on. Also, I believe the computers are setup correctly because, like I stated, the wake-on-LAN works perfectly if I power on and off the computer first.
Any other ideas?
A NIC that supports WOL will remain live even after the machine is shut down. It will continue to recieve broadcasts and listen for a “Magic Packet” or other various events. Switches recieve a frame, add the source MAC address the the corrisponding port. If the destination is unknown the switch will then flood the frame out all other ports with the exception of the port that it was recieved on. Bottom line, if a switch doesn’t have a mac address in its table, it floods all ports (except the port it was recieved on) with the frame.
A WOL-enabled device, when powered off, will still draw a tiny amount of electricity to drive the NIC. The interface remains in a passive, listening mode, sending nothing out on the network. To wake up the device, a specially formed packet is sent to the network port where the device is plugged in. This packet – the magic packet, carries a specific “signature.” When the NIC sees this signature, it recognizes this as a wakeup call. So once put into the magic packet mode it will scan all incoming frames waiting for the signal. You should not have to change anything on the Switch, it is all about the NIC and what you are using to call the WOL to be provoked on the workstation. Does this help?
eDuTek,
That does help; maily the part about the switch flooding all ports. That was unclear to me. I did add the computers MAC addresses into the switch statically. I will remove the static commands and see if it still works.
So you are saying that wake-on-LAN should still work even if the switches do not list the MACs in their address-tables because the switch will flood all ports with the packet? Is this correct?
If after removing the static MAC entries, the computers do not turn on, I will re-check the BIOS settings.
Thanks for all your help.
What are you using to wake up the PCs? Are you certain the MAC addresses are correct? You might test this software: http://www.depicus.com/wake-on-lan/wake-on-lan-gui.aspx to see if it works.
Worst case, you could setup STICKY MAC addresses on the switches that will dynamically learn and remember the MACs of the attached computers. The only problem with this is that you have to setup port security to learn these addresses. When port security is off, the MACs are dropped when they are not used for a short period of time. If you want to test your configuration, the commands to do this are:
-interface range fa 0/1 – 48
-switchport port-security mac-address sticky
-switchport port-security
You might also need the following:
-switchport port-security maximum # (maximum hosts)
-switchport port-security violation shutdown|restrict|protect (restrict is probably what you want)
This causes some problems if you leave the implied default of “switchport port-security violation shutdown” as when you have two MACs on a port, the port will shutdown and not come back up without Network Admin intervention. You’ll have to delete the sticky mac address from the interface configuration, shutdown the port and bring it back up. Restrict will work better for you on this. Moves, adds, and changes will keep the old mac addresses until they are manually cleared out.
In any case, this isn’t the proper way to do this as the previous poster states. It’s a work around for the time being until you can test out your configurations and what your switches or systems are doing.
SF
eDuTek is correct about the packet being sent to all ports if nothing is the the MAC table. This a normal feature of broadcast. If the subnet recieving the message to a specific IP address does not know the MAC, it does a broadcast to see if anyone has it. The NIC knows it’s static IP address and if it gets the broadcast “magic packet” of “who has x.x.x.x” it responds “I DO!”, and wakes the PC.
check out this site http://www.matcode.com/wol.htm
save the executable in the sytem32 folder. create a batch file listing each machine you want to wake up:
mc-wol XX:XX:XX:XX:XX:XX /a 192.68.1.1 ‘Host of netbios name
you can use task manager to schedule the wol if you want to. i am running this off of my xp sp2 machine.