I wish I had discovered how to do this years ago. Need to determine the admin IP of a firewall switch or other network device on the same switch that you are plugged into?, here is a slick way:
First determine the MAC Organizationally Unique Identifier (OUI), which is the first half of the MAC address. There are various databases online to determine this by vendor/device. Once you determine it issue the commands below (my commands have mimosa MAC as an example)
Windows / DOS: arp -a | findstr 20:B5:C6
Mac / Linux: arp -a | grep 20:B5:C6
The above commands will query the arp table of your computer and output the IP of any mac addresses that match the string. Slick! Remember you must be directly connected to the device.