What happens when a frame with an unicast destination MAC address is not in the MAC address table of a switch?

What happens when a frame with an unicast destination MAC address is not in the MAC address table of a switch?

• A. The switch will drop the frame
• B. The switch will forward the frame out all ports except the incoming port
• C. The switch will only forward the frame to the default gateway
• D. The switch will request the MAC address from the sending device

Answer: (B)

When a switch receives a frame with a unicast destination MAC address that is not present in its MAC address table, the correct action is to forward the frame out of all ports except the one on which it was received. This is known as flooding. The reason the switch behaves this way is based on the principle of learning and building its MAC address table. When the switch does not have an entry in its MAC address table for the destination MAC address, it assumes that the destination device could be located on any of the other connected network segments. By flooding the frame, the switch ensures that the frame has the best chance of reaching its intended destination. Once the destination device responds, the switch can learn its MAC address and update its MAC address table for future communications, directing frames to it more efficiently. In contrast, the other options about dropping the frame, forwarding it only to the default gateway, or requesting the MAC address from the sending device are not operations performed by a switch under these circumstances. The primary function of the switch in a typical network environment is to ensure that network traffic flows to intended devices, and flooding is a crucial method to facilitate that when precise routing information is lacking.

When a switch receives a frame with a unicast destination MAC address that is not present in its MAC address table, the correct action is to forward the frame out of all ports except the one on which it was received. This is known as flooding.

The reason the switch behaves this way is based on the principle of learning and building its MAC address table. When the switch does not have an entry in its MAC address table for the destination MAC address, it assumes that the destination device could be located on any of the other connected network segments. By flooding the frame, the switch ensures that the frame has the best chance of reaching its intended destination. Once the destination device responds, the switch can learn its MAC address and update its MAC address table for future communications, directing frames to it more efficiently.

In contrast, the other options about dropping the frame, forwarding it only to the default gateway, or requesting the MAC address from the sending device are not operations performed by a switch under these circumstances. The primary function of the switch in a typical network environment is to ensure that network traffic flows to intended devices, and flooding is a crucial method to facilitate that when precise routing information is lacking.