200-301 Question 160
Single answerA network administrator is troubleshooting an issue where a switch is flooding frames to all ports, even though the destination MAC address is a known unicast address. Which of the following scenarios is most likely causing this behavior?
- A
The MAC address table of the switch is full, and new entries cannot be learned.
- B
The switch has Spanning Tree Protocol (STP) disabled, causing loops in the network.
- C
The destination MAC address is not in the switch's MAC address table.
- D
The switch is configured with an incorrect VLAN on its interfaces.
Show answer and explanation
Correct answer: C
Explanation
Frame flooding occurs when a switch receives a frame destined for a MAC address that it does not have in its MAC address table. In this case, the switch forwards the frame out of all ports in the same VLAN, except the one on which the frame was received. This behavior is a normal part of switch operations when handling unknown unicast traffic. The scenario's most likely cause is that the destination MAC address is not in the switch's MAC address table.
- A. Incorrect.
If the MAC address table is full, the switch will typically start flooding unknown unicast frames. However, this is not the most likely cause in this scenario because the question specifically mentions the MAC address of the destination is known.
- B. Incorrect.
While disabling STP can cause network loops and excessive flooding, this scenario does not mention loops or broadcast storms. Frame flooding due to loops behaves differently than flooding caused by unknown MAC addresses.
- C. Correct.
If the destination MAC address is not in the switch's MAC address table, the switch will flood the frame to all ports in the VLAN, as it has no way to determine the correct destination port. This is the most likely cause.
- D. Incorrect.
An incorrect VLAN configuration could cause communication issues, but it would not directly result in frame flooding for a known unicast address.