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I know I can ping and find the MAC address in my local arp table.

But what if a computer I want the address to is not started and can't respond to ping etc. and I cant reach it physically. Is there somewhere I can find this MAC address?

For example in routers or in DNS tables or something?

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3 Answers 3

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No you cant. Unless you have any mac-based rule on the switchport

Edit: dns reservations ( as you mentioned ) and dhcpd leases can work too.

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Yes, DHCP leases would work, unfortunately it uses a fixed IP set locally. –  Andreas Pettersson Aug 21 '13 at 12:43

you may be able to find it in the Arp Cache of a system that had discovered the computer, if you know the downed PCs IP address.

in Windows:

arp -a

in Linux

arp
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Thank you, I tried that but that computer wasn't listed. I ran arp -a from a Windows 2012 Server which is a Domain Controller and DNS server. The client PC i want to find was connected to it about 12 hours before and are joined to the same domain. Regards Andreas –  Andreas Pettersson Aug 21 '13 at 12:30

If the computer have BIOS set up for remote start, you should be able to send "magic packet" to it, to turn it on and then wait for its startup for network access.

Look for "Wake on LAN".

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Umm you need the MAC address to use Wake on LAN, and the question is all about how he doesn't have the MAC address. –  nhinkle Aug 21 '13 at 21:08
    
This was actually the reason for asking, i needed the MAC address to be able to do a WOL. :) –  Andreas Pettersson Aug 22 '13 at 7:14
    
It is hard to do, but with a self-written application, you can turn on this computer by sending magic packets in local network that would just try every MAC address. The scope would be limited if you know the Ethernet adapter manufacturer (first digits of MAC). This would take much time and in effect you would turn on all the computers in local network, that have WOL active. –  pbies Aug 22 '13 at 16:03

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