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Wake on LAN ???

madswitcher
Grafter
Posts: 235
Registered: 01-08-2007

Wake on LAN ???

Hi All, I have been playing with wake on LAN and got it to work fine. The config is:

My machine, firewall, DMZ, firewall, modem, WAN

The target machine is in the DMZ and connected via a switch into the internal switch of the second firewall.

All works hunky dorey in that I close the target down, immediatly send it a magic packet and it wakes up. However, if I leave it for about 15 minutes, it won't respond to the magic packet.

Any ideas?

Thanks, Mike
5 REPLIES
pacem
Grafter
Posts: 175
Registered: 07-09-2007

Wake on LAN ???

This is an educated guess with the emphasis on the guess side of things...

Your machine is connected via a switch, after 15 minutes it loses track of your machine's location. I bet if you send the WOL signal from a machine connected to the same *hub* then it would work.
If you don't have a hub you may be able to verify this by watching the lights flash on your network socket.

Paul.<><
Community Veteran
Posts: 14,022
Thanks: 540
Fixes: 9
Registered: 01-08-2007

Wake on LAN ???

pacems answer sounds about right and would probably be the most likely.

I have WOL working on 2 machines currently (soon my 3rd when I track down that elusive wol cable for an older P3 motherboard). They're all connected via the same switch and I've never experienced anything like you describe.

Most modern switches are supposed to learn a table of all mac address's etc but when the machine powers down I got a funny feeling the switch might be recognising yours as a disconnection. When I shut mine down, the NIC remains powered up and the switch recognises this as the LED for that ethernet socket remains lit up.

I don't know what switch your using but if it has LEDS see if the one for the PC in question is still lit up when you try.

I know it's frustrating - WOL is so useful and yet it can also be one of the hardest things to get working properly.
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madswitcher
Grafter
Posts: 235
Registered: 01-08-2007

Wake on LAN ???

Hi chaps

Thanks for the steer. I did some more research on this problem and found that it is switch related. I have a couple of managed switches - i.e. they have some form of intelligent control in them, and they seem to drop the MAC table entries if not used for some time.

Whereas as pretty simple switch retains the MAC entries ad infinitum. So the principle here is to use dumb switches for any WOL implementation.

Nice bit of detective work -thanks for your help

Mike
N/A

Wake on LAN ???

The availability of MAC tables should not really be relevant, as the "magic packet" uses a broadcast message which should go to all connected computers (ie those with a power supply that provides a standby voltage). A problem arises when packets have to go through a firewall, then a port has to be defined for the message to use.

If required, the WOL cable must be connected for it to work (all discrete cards and some on-board hardware).

There are obviously some other effects, as when I try to wake 20 computers (same hardware, BIOS settings, switch), a random selection will start!
Community Veteran
Posts: 14,022
Thanks: 540
Fixes: 9
Registered: 01-08-2007

Wake on LAN ???

Quote
The availability of MAC tables should not really be relevant, as the "magic packet" uses a broadcast message which should go to all connected computers (ie those with a power supply that provides a standby voltage). A problem arises when packets have to go through a firewall, then a port has to be defined for the message to use.


Yes it does make a difference. If the MAC table does not contain a MAC address for a specific PC, then the switch thinks there is nothing on that socket connected. Therefore it won't transmit the data packet to nothing. It simply thinks there is nothing connected to that particular socket.

@Hastings1066, where abouts in hastings are you? - I'm in the Ashford/Tenterden area and I frequently come down there to see my GF's relatives. If you like, I can bring my sitecom 5 port switch down for you to try (not a managed switch, just a normal one). You can try it out for 1/2 hour and see if that resolves the problem. If your interested leave a reply here or PM me.
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