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If two computers are connected by ethernet directly (ie, with no router between them) can one computer wake the other using the magic packet?

I ask because it's not working for me and I'm not getting very useful search results. If someone can confirm that this should indeed work then I can check and re-check the system settings and specifications.

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How are the two systems connected? gigE? 100mbit? are you using the right cable (eg, gigE ports should auto-flip the tx/rx to accommodate direct connections like this, but 100Mbit would need a cross-over) –  Travis Campbell Feb 1 '12 at 16:17
    
One NIC is 100Mbit and the other is 1000Mbit, never thought about that before. –  Matt Feb 1 '12 at 16:20
    
Do the systems communicate when on? –  Zoredache Feb 1 '12 at 16:37
    
Yep, they work fine when on. –  Matt Feb 1 '12 at 16:59
    
Is the port lit up on both sides even when the computer is off? If not, then wake on LAN isn't correctly configured or isn't supported. –  David Schwartz Feb 1 '12 at 16:59
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2 Answers

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1) You need a cross-over ethernet cable.

And it is probably best to manually configure both computers for 100 MB, full-duplex.

You can never rely on auto-negotiate to work correctly when hooking up 2 computers directly. Especially not if they use different line-speeds by default (Gb and 100Mb in your case).

Auto-negotiate is only properly defined for computer to switch connections using standard (non-crossover) cables. The Gigabit standards adds support for cross-over cables and automatic cross-over when needed, but only if BOTH sides of the connection are Gigabit.

If negotiation fails the behavior is undefined: Murphy's Law then applies: It won't work.

2) Don't forget to configure the computer that needs to sleep/wake up properly. Wake up on LAN (WOL) must be enabled in BIOS and in the Operating System.

(On Windows make sure in the device properties of the LAN card that "This device may wake the computer" is enabled.) You may have to upgrade the BIOS and/or the network-drivers to make this possible.

PS: Simple check if BIOS/drivers is setup correctly and the cabling is right:

Shut down the computer that needs to go down/wake up. If the network-light on the back is still burning while the computer is off you are good to go.

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What's the difference between a standard cable and cross-over cable? I didn't know there was a difference so I'm probably not using a crossover cable. The computers communicate fine when they're actually on, so does this indicate that the cable isn't the problem or will it still need to be crossover? –  Matt Feb 1 '12 at 17:02
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Normal cables are the norm so you probably have one of those. The pinout is different. A standard cable has pins 1 to 8 connected 1 on 1 to the other side. A cross-over has pins 1-2 connected to 3 and 5 on the other end (and vice-versa). If the computers currently can communicate doesn't mean it will work when one is off. The normal auto-negotiate rules may or may not apply in that case. It can not be predicted what will happen. It depends on too many variables. If the link-light on the OFF computer remains on when it's off you are fine. –  Tonny Feb 1 '12 at 19:07
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Yes, if the cable is a crossover cable. Otherwise you'd need a switch of some kind. Some NIC's autosense and can switch over for you, or you can get a device that "adapts" the connection for you. Otherwise make your own cable with the crossover wiring.

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