Is a network interface supposed to have no more than one MAC address?

Since a network interface is free to have more than one IP addresses, is IP address a way of multiplexing MAC address, if a network interface is supposed to have just one MAC address?



An interface using a protocol with MAC addressing (not all layer-2 protocols use MAC addressing, some have other addressing, and some have no addressing) will only have a single unicast MAC address. The interface will respond to the broadcast MAC address and the MAC addresses of any multicast groups to which is has subscribed.

Your question seems to indicate that you do not really grasp the purpose of the different network layers. Layer-3 addresses, e.g. IP addresses, define the logical network(s) to which the interface belongs, and it can prove difficult (depending on the host OS) to assign more than one IPv4 address to an interface, although IPv6 easily uses multiple addresses on a single interface. For protocols that use MAC addressing, the MAC address is the address on the physical network. Having multiple MAC addresses on an interface would be like having multiple physical street addresses on your house; it may not be impossible, but it doesn't make much sense.

The MAC address is simply to get frames from one host on the LAN to another host on the same LAN, and the interface is only connected to one LAN. On the other hand, an interface could belong to multiple logical networks, which is why you may have multiple network addresses. Network addressing is to get packets from one network to a different network.


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