Mac – Find MAC address of a device on the other end of an Ethernet cable

Standard 100 base ethernet only uses two pairs so this works... what is a little worrisome is it appears someone did it on the cheap and saved a couple of cents by omitting the other pairs. That said, 1000 base ethernet may use all four pairs and this cable can't handle that.

I'm going to assume that "at work" they are connected to a network with DHCP, and the addresses you mentioned were assigned dynamically (or perhaps DHCP reservation).

If you connect the device directly to your PC, you will have to rely on APIPA addressing, which isn't very reliable or easy to work with.

Instead, connect the device to your home router. Your router will automatically assign it an address on the same subnet as your home PC. To find the address that your router has assigned it, log into your router, and look for the "client list" (sometimes referred to as a table, status, etc.) It will be a little different depending on your specific router, but here is an example of how to do this step-by-step with a Linksys router. Below is a picture of the client list from a TP-Link router.

Ideally it will be named something identifiable to you. If not, just try the address of each client until you get a connection.