Find MAC Address of remote machine using its IP address?

If you ping the computer you can find the MAC address in the arp cache.

Open a cmd and put in: arp -a

With the free GFI Security Scanner you can also scan the IP-Adress.
http://www.gfi.com/lannetscan/

Ah.. sorry.. you can't get it with ARP if your not on the same Subnet. My BAD...

Only two ways to get that if your not on the same network.

A - You hack their computer.....hahha....i'm sorry...
B - You hack into the router, firewall, or modem and read their dhcp wired/wireless connections list.  Assuming they are using DHCP on whatever hardware device they are using to connect......

If your not on their network...you have to hack a device that is to find the MAC id..

btw....why would you want their Mac id anyway....?

That kind of info is only useful to the FBI or CIA.

Because a Mac Id can trace back to the exact point of time the networkcard was manufactured, in what city, state, zip, the computer system it utlimately wound up in when it was sold, and purchased with whoevers credit card.  A MAC Id is much like a serial number on a gun.  But unless your the FBI or CIA, I doubt a Mac Id is going to help you with stopping the troublemaker.  

FYI: Definitely there are privacy issues here -- Beware!
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Maybe better to block/deny the IP access to your PC/Network.

Simple answer is, if it's not on a network you control, you can't without some kind of hack or spyware which you could get onto the target and report back to you.  If it's on a network you control, you look in the MAC forwarding table of the switch it's connected to, if you know the port, or you look in the ARP table of the default gateway for the IP network it's attached to.

We're using a Motorola Canopy wireless wan. The Canopy system acts like a big hub/broadcast domain. Some user has hooked their pc directly to their antenna and their pc has a virus or is running some sort of scanner/pinger. It is flooding the network with pings. Their signal goes from their antenna, through the backhaul antenna on the mountain/tower back out the backhaul antenna and over to our main backhaul unit on top of our main intertie with sprint fiber.

The problem is that I can block this guy at the intertie but cant figure out which/whos antenna is the offending unit and its killing the backhaul connection...which kills everyone :)  So I can get his MAC which by the way changes at random, so this may not help, I can eventually figure out who it is.

FBI, no,,,,ISP :)

If he's on your OWN network, then you can ping it and look at the arp entry on your machine by typing ARP -a in a command line.  Otherwise, examine the ARP table on your default gateway.

Matrix1000:  I also work for a wisp that uses Canopy gear...  maybe we can network and share experiences to help manage this stuff better.  Drop me a line at robtullis(at)yahoo.com if you are interested.