350-401 Question 134
Single answerA network engineer is configuring Rapid Spanning Tree Protocol (RSTP) on a campus network. To enhance network stability, they also enable BPDU Guard on access ports. During testing, one of the access ports connected to a user's device goes into an 'err-disable' state. What could be the most likely reason for this behavior?
- A
The user's device sent a Bridge Protocol Data Unit (BPDU) on the access port.
- B
The network engineer enabled Root Guard instead of BPDU Guard on the access port.
- C
The access port received an excessive number of frames, causing it to shut down.
- D
The spanning tree protocol on the user's device was not configured properly.
Show answer and explanation
Correct answer: A
Explanation
BPDU Guard is a Spanning Tree enhancement designed to protect the network by preventing BPDUs from being processed on ports that are expected to be edge ports (access ports). If a BPDU is received on a port with BPDU Guard enabled, the switch will place the port into an 'err-disable' state to prevent potential network instability. In this case, the user's device likely sent a BPDU, triggering the BPDU Guard protection mechanism.
- A. Correct.
BPDU Guard is designed to disable a port if it receives a BPDU. This is the expected behavior when BPDU Guard is applied on an access port and a BPDU is detected.
- B. Incorrect.
Root Guard does not cause a port to go into 'err-disable' state. Instead, it prevents a port from becoming the root port if a superior BPDU is received.
- C. Incorrect.
Excessive frames would not cause a port configured with BPDU Guard to go into 'err-disable' state. This is unrelated to BPDU Guard functionality.
- D. Incorrect.
Spanning Tree misconfiguration on the user's device is not the direct cause of the 'err-disable' state. BPDU Guard specifically reacts to the presence of BPDUs on access ports.