Why does a switch flood a frame to all ports?
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A. B. C. D.D
Switches use the destination MAC address in the frame header to forward frames to the correct destination. When a switch receives a frame, it looks up the destination MAC address in its MAC address table to determine the port to which the frame should be forwarded. If the MAC address is in the table, the switch forwards the frame only to the appropriate port. However, if the MAC address is not found in the table, the switch floods the frame to all ports (except the port on which the frame was received).
Therefore, the correct answer is B. The destination MAC address of the frame is unknown.
This process is known as unknown unicast flooding, which occurs when the switch does not have an entry in its MAC address table for the destination MAC address of the frame. The switch floods the frame to all ports (except the port on which it was received) in an attempt to find the destination device. The destination device will then receive the frame and respond to it, allowing the switch to update its MAC address table with the correct port information for that device.
Unknown unicast flooding can also occur if the MAC address table is full or if there is a network loop that prevents the switch from determining the correct forwarding port for a frame.
Option A (The frame has zero destination MAC addresses) is incorrect because every Ethernet frame has a destination MAC address.
Option C (The source MAC address of the frame is unknown) is also incorrect because the switch does not need to know the source MAC address to forward the frame to its destination.
Option D (The source and destination MAC addresses of the frame are the same) is also incorrect because it is a valid scenario, such as when a device sends a frame to itself for testing purposes.