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I know that MAC address is a physical address attached to Network Interface Card(NIC) to identify your computer uniquely. However, MAC address of Ethernet NIC or Wireless 802.11a/b/g/n WiFi NIC are different.

  1. So, does it mean a laptop can be identified with 2 different MAC address depending on the network interfaces it supports?(Wifi/Ethernet or both)

  2. Also, modem has MAC address found on the bottom of the Modem. Why does modem has a unique MAC address on your home network besides laptop, phone and other devices connected to the Internet?

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So, does it mean a laptop can be identified with 2 different MAC address depending on the network interfaces it supports?(Wifi/Ethernet or both)

Yes. The MAC address identifies the interface, not the laptop. Every interface will (should) have a unique address.

Also, modem has MAC address found on the bottom of the Modem. Why does modem has a unique MAC address on your home network besides laptop, phone and other devices connected to the Internet?

Because the modem had an Ethernet interface, it has a MAC address.

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1: Yes it does. Theoretically you can add as much NICs as you want to your device, you are able to be identified. But layer two adresses aren't the only attributes which are needed to identify a device. The hardware, the software and user behavior is used nowadays (at least in the world of the ads). The more information you announce, the better you are able to be identified.

2: Network communication without layer two is unusual or rather not possible (at least for most, there might be other ways which I don't know). IP is based on MAC. Thereforce the modem needs to have a mac adress to communicate via IP with the WAN.

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