Hardware address of an interface (e.g., Ethernet, Wi-Fi)
6 bytes (48 bits) as hexadecimal: aa:00:bb:fe:24:3a
Ethernet network interface controller (NIC)
Switches
The frame is destined for only a single host, b1:b1. But since the switch doesn't know to which port b1:b1 is attached, the switch needs to flood the frame out on all ports, except the sender's port.
When the switch receives a frame on a port, it saves the source MAC address of that frame in the switch's MAC address table.
