Understanding Switch Flooding
Question
Why does a switch flood a frame to all ports?
Answers
Explanations
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A. B. C. D.C.
A switch uses its MAC address table to determine which port to forward a frame on based on its destination MAC address. However, there are several scenarios in which the switch may flood a frame to all ports:
A. The frame has zero destination MAC addresses: This scenario is unlikely to occur as a frame must have a valid destination MAC address to be sent on the network. If the destination MAC address is zero, the switch will drop the frame.
B. The destination MAC address of the frame is unknown: When the switch receives a frame with a destination MAC address that is not in its MAC address table, it floods the frame to all ports except for the port on which it was received. This is known as unknown unicast flooding. The switch does this to ensure that the frame reaches its intended destination, as the destination MAC address may be on a device that has not yet communicated with the switch and therefore is not in its MAC address table.
C. The source MAC address of the frame is unknown: If the source MAC address of the frame is not in the switch's MAC address table, it adds the source MAC address to the table and then forwards the frame out the appropriate port(s). If the source MAC address is unknown, the switch will flood the frame to all ports except for the port on which it was received. This is known as broadcast flooding. The switch does this to ensure that the frame reaches its intended destination, as the destination MAC address may be a broadcast or multicast address.
D. The source and destination MAC addresses of the frame are the same: If the source and destination MAC addresses of the frame are the same, the switch will flood the frame to all ports except for the port on which it was received. This is known as loopback or self-flooding. The switch does this to ensure that the frame reaches its intended destination, as the destination MAC address may be a broadcast or multicast address.
In summary, a switch floods a frame to all ports when it does not have enough information to forward the frame out the appropriate port(s), such as when the destination MAC address is unknown or the source MAC address is unknown. The switch does this to ensure that the frame reaches its intended destination and is not lost on the network.
