So in case your network card goes boom, the new card you replace it with will have different MAC address and so the Internet wont work. Your ISP uses MAC address to identify or authenticate your Internet connection.I am listing some of the legitimate reasons while you wonder what the other reasons might be! There are many reasons you would want change MAC address, some legitimate others not so. So, clearly this is not a reason to change MAC address! And when an Ethernet frame reaches a router, the router's MAC address is used to send the frame forward. Its because, MAC address is used as unique identifier at data link layer (OSI layer 2), like for example your local Ethernet, while the IP packet being forwarded over Internet is at network level (OSI layer 3) and uses IP Address as a global unique identifier (which websites can see and track). Some people think that websites on Internet can track users using MAC address and so they must change it! Well, your MAC address wont go further than the first router the IP packet gets to.
Many people are clueless that you can even change MAC address and give open challenges, so forget that they would know why there is a need to change a MAC address. I have been asked many times this question, in person as well as over email.
