Home routers almost all had MAC cloning as well. ISPs would send a technician out to set up service and would only want to connect the modem to a single system.

Home routers almost all had MAC cloning as well. ISPs would send a technician out to set up service and would only want to connect the modem to a single system. The modem would then lock onto that MAC and refuse to connect to other hosts. So home routers would clone that system's MAC address on the WAN port so the shitty modems wouldn't complain. At the time many broadband ISPs expected you to sign up a new broadband account for each connected machine. They'd balk if you mentioned connection sharing, I had an AT&T CSR go so far as to tell me it was illegal. This idiocy subsided as WiFi became more common and added directly to home routers.