Sometimes it’s necessary to discover the MAC address of a remote system on a network quickly (for example when setting up DHCP scope reservations). It’s fortunately a really easy process to determine this information.
First of all, ping the remote host, then run an
arp -a
at the command line. This will give you the MAC details. The catch is that this only works on the same subnet – when trying to do this on a remote subnet (on the other side of a router, etc) you won’t get a response…there is a solution for this though, as long as the remote host you want to determine the MAC for is a Windows host.
NBTscan is a tool that can do this (and is available from the repositories on most linux distros (or at least on Debian, Ubuntu and Fedora, and is also downloadable for Windows 
)