How to Go Everywhere at the Same Time

How to Go Everywhere at the Same Time

So far, when discussing MAC addresses (in other words, Ethernet addresses), I have always implied that a MAC address represented an individual NIC attached to a LAN. Well, it is true that many MAC addresses represent individual NICs. Addresses that represent an individual NIC are called unicast MAC addresses.

Ethernet also defines a special MAC address, called the broadcast address. The Ethernet broadcast address is FFFF.FFFF.FFFF. When a computer sends a frame with a destination address of FFFF.FFFF.FFFF, it means that the frame should be forwarded to all devices on the LAN.

So, imagine that a switch receives a frame, a frame whose destination MAC address is the broadcast address. What should it do? The switch simply floods the frame out all ports (except the port in which it was received), as shown in Figure 6-11.