It’s an ethernet wire that’s going to be exiting my house and running to a camera in a publicly accessible space. An attacker could disconnect the camera, connect a laptop and access my network. How could I protect against that (other than a physical lock)? I basically want to lock down that cable to the point where nothing works on it unless it’s the intended camera. If this was wireless, I’d just use MAC filtering, but I don’t see an equivalent for wired connections.
As others have suggested you can do port based MAC filtering on some switches. There are also physical cable locks that I’ve played around with from Panduit (and other vendors), but they won’t prevent someone determined to disconnect it, but a good deterrence. Some switches also have security settings where if a port status goes down it will keep the port offline, so if someone disconnected the camera they would be plugging into a dead wire.