In chart 1, there is a layer 2 that switches without setting VLAN. Any
broadcast frame will be transmitted to the other ports except the send port.
For example, a broadcast information is sent out from port 1 then
transmitted to port 2,3and 4.
In chart 2, red and blue indicate two different VLANs in the switch, and
port 1 and port 2 belong to red VLAN, port 3 and port 4 belong to blue
VLAN. If a broadcast frame is sent out from port 1, switch will transmit it
to port 2, the other port in the red VLAN and not transmit it to port3 and
