My computer MAC Address has been registered in a specific wired LAN network. But yesterday, I had my laptop repaired and the motherboard was replaced. Therefore, it has a new MAC Address and it cannot connect to the network anymore.
How can I find the old MAC Address, so that I can possibly spoof it to get back on the network? Unfortunately for various reasons it is not possible to add the new MAC to the registry.
I am using Yosemite version 10.10.3.