In a LAN, stations use the Layer 2 MAC address
in a frame to identify the source and
destination. When Station 1 transmits to Station 2 in the Figure,
Station 1 generates a frame that includes the Station 2 MAC address
(00-60-08-93-AB-12) for the destination and the Station 1 address
(00-60-08-93-DB-C1) for the source. This is a unicast frame. Because
the LAN is a shared media, all stations on the network receive a
copy of the frame. Only Station 2 performs any processing on the
frame, however all stations compare the destination MAC address
with their own MAC address. If they do not match, the interface
module of the station discards (ignores) the frame. This prevents
the packet from consuming CPU cycles within the device. Station 2,
however, sees a match and sends the packet to the CPU for further
analysis. The CPU examines the network protocol information and the
intended application and decides whether to drop or use the packet.
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