I have an IP address of a computer which I am currently away from, and I need the MAC address. 
How do I get the MAC address if I ony have the IP?
If you are on the same network you can open up a Terminal:

ping your_ip_address


hit Ctrl-C on the keyboard to stop pinging then do a:

arp -a


a list should appear, look for the ip you just pinged and next to it is the MAC address of the device.
