How to find the MAC address of a 'shutdown' system on local lan (is it possible?)

Question

How to find out the mac address of a system which is:

1. Shutdown
2. Power plugged in
3. Connected to Lan
4. Nic card ON.

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Update I am asking how to find out the mac address of some other system which is already shutdown.... and which is on lan..

I want to find out its mac from my system.... and to be clear... I want to tell that.. arp table can be populated by using ping .. i.e. if 172.16.3.12 is not in arp table then it can be added by just ping 172.16.3.12 but a system can be pinged only if its on ... a shutdown system can't be pinged...

Trimetric

@pirates, you need to lookup ARP, the address resolution protocol, but keep in mind that you'll need to ensure that the machine you're looking for is on the local subnet since otherwise, ARP will give you the MAC address of your local router (so the packet can be sent out properly). And the urgency to you is of absolutely zero concern to anyone else, so that last line is a bit of a throwaway :-) – Sapphira

@close voter: I don't see this as a duplicate of that (#1333844). This question is about finding the MAC address of a different machine; that one is about finding the MAC address of the host on which it's running. – Leiker

Why is this being voted down without providing a reason? True, it should probably go to serverfault/supersuser (I don't understand those mechanics) since a 'shut down' machine will not run any code locally ... but the question is legit! – Ascend

of course a shutdown machine will not run any code locally.. but when in the earlier version of wake on lan...when we send the magic packet to a MAC address which is already known...then it gets on.. HOW?? the mac address is of NIC card..and when it sees its mac address in the magic packet ...it responds by switching on the system...so was there any code executed...but still the mac address was identified...and when it can be identified by some means...then y can't be found!!! please reply – Trimetric

You must find the mac address of your system BEFORE you shut it down (you probably know). You must also configure the system to WOL (you also know). If the system cannot be configured to your WOL technology => bad luck, no can do! – Ascend

Assume its configured... My question is very simple... please... i am only asking how to find our the mac address of another system on lan which is *shutdown AND *power plugged in AND *nic card on AND bios settings configured... please provide a valid solution... – Trimetric

I know of none (except reading the MAC from a label on the box:-) – Ascend

One way is to find an exploit in the WOL code of your NIC's firmware. Another way is to call that computer's owner/operator on a telephone, pose as a technician, and have him read off the MAC address from the sticker on the case. – Africanist

ya..nice solution mr.codewearrior... thank you for your valuable time... – Trimetric

Answer 1

Once the system is shutdown your best bet to finding the MAC address is looking for stickers somewhere on the case!

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Seriously, I guess you are looking for some way to "wake on lan" a computer on a local lan?
I'm not certain that the machine would respond (be supposed to respond) to anything unless you know the mac already and can the correct magic packet.

From the wikipedia article I linked:

How it works

Wake-on-LAN is platform-independent, so any application on any platform that sends magic packets can wake up computers running on any platform. It is not restricted to LAN (Local area network) traffic.

The computer to be woken is shut down (sleeping, hibernating, or soft off; i.e., ACPI state G1 or G2), with power reserved for the network card, but not disconnected from its power source. The network card listens for a specific packet containing its MAC address, called the magic packet, broadcast on the broadcast address for that particular subnet (or an entire LAN, though this requires special hardware or configuration).

Ascend

thank you lexu.. yes, your guess is right..i am making wol.. but a bit different from the earlier version.. in the earlier versions we have to provide the mac address ... but now i only have the host name or the ip address... and now i want to wake it on lan.. for this i want its mac address..and thanks for the wikki stract..but i already gone through it... well thanx for the reply.. – Trimetric

I don't think you can WOL a shutdown machine without 'knowing' something 'privileged' about it. Also this machine needs to be "willing" to be woken. Are those conditions met? – Ascend

yes...To make a machine to be "wiiling" to be woken...we just need to make some changes in bios setting in power tab... these condistions are met... so any valid solution please.. – Trimetric

As I said above: knowing the MAC (or an equivalent somewhat private token) address is a precondition for WOL. You cannot WOL an alien system. – Ascend

No doubt you are right mr.lexu.. but i am asking that only...GET THE MAC ADDRESS... please read my query once again...please... – Trimetric

@pirates-iiita: I thought I had read your question (steps 1-4) and I stand by my statement: The MAC-address must be known BEFORE SHUTDOWN or you cannot WOL. There are Answers here on stackoverflow that will show you how to get the MAC of a running system (either locally or using local lan). Somehow we are not communicating. I don't seem to understand your question!! – Ascend

Answer 2

arp -a ip-address if you know the IP address that the PC typically receives from DHCP, or if it has a static IP.

The PC on which you run the arp command may yet have this information in cache. I just did this from home by logging into a remote desktop session on one of my servers. The server I logged into still had my PCs infomation in the ARP cache even though my PC was not responding to ping.

Initially I logged into my DHCP server to see if my PC still had a lease because that will list your MAC address, and it will show your PC's name. Unfortunately for me, my PC has a very short lease and so it was not in the list.

Fortunately, I happen to know the IP address that my PC typically obtains from DHCP, so I was able to use the above arp command.

Using this information I was able to send a magic packet to my PC and wake it up. This I did using a free utility I found after a brief Google search.

Coverall

Answer 3

Yes, I once tried to implement a data-center-wide power management system based on Wake On Lan technology. I had a number of solutions, but never got to implement them because the data center people decided that the reliability costs involved in shutting down and powering back up were higher than the energy savings.

A couple of random observations:

My experience was that the routers forgot the mac addresses after the machines had been shut down for more than 20 minutes. After that, the mac addresses were lost until the machines next powered up. Obviously, this will vary depending on the actual router used, but 20 minutes is probably pretty typical.

This means that in practice, the only way to get the mac address is to obtain it BEFORE you shut the system down. I'm not sure what your application is, but I think you can probably find a way to do this one way or another.

Once the router has forgotten the mac address, there's no way to deliver the WOL packet to the machine to be woken from outside the network. From inside the network, you can still do it with a broadcast packet. Either way, you still need to know the mac address, since it's part of the WOL packet.

Now theoretically, you could modify the firmware in the NIC chip to allow it to respond to ARP packets even when the machine itself is powered off. This may even be common practice -- I don't know. If so, what you want to do is do-able, but would be highly dependent on the exact network interface you have.

Adallard

Answer 4

try to use getmac command

example: getmac /s [IP address] but i cannot know the mac address of computer turned off by this command

Savil

Unfortunately, OP wants the mac address of a shut-down system. It presumably won't be responding to ARP requests. – Adallard