Switch Flooding for Unknown MAC Addresses | Generated by AI
Question: In Ethernet switching, what happens when a switch receives a frame with a destination MAC address that is not in its MAC address table?
Answer:
When an Ethernet switch receives a frame with a destination MAC address that is unknown (not present in its MAC address table), it performs flooding. The switch forwards the frame out all ports except the incoming port on which the frame was received. This ensures the frame reaches the intended destination if it is connected to the switch, while allowing the switch to learn the destination’s port when a reply comes back.
This behavior is fundamental to how Layer 2 switches operate in unknown unicast situations.
- Option A is incorrect: The switch does not drop the frame; dropping would break connectivity for unknown destinations.
- Option B is correct: Flooding out all ports except the incoming one.
- Option C is incorrect: Sending to the default gateway is a Layer 3 (router) function, not a Layer 2 switch.
- Option D is incorrect: Buffering indefinitely is not standard behavior; the switch forwards the frame immediately.
The correct answer is B.
References:
- Cisco - Understanding and Configuring the Switch CAM Table
- IEEE 802.1D - Media Access Control (MAC) Bridges