350-401 Question 124
Select 2A network engineer is troubleshooting a Layer 2 issue in a switched network. Hosts in VLAN 10 cannot communicate with each other, even though they are connected to the same switch. Upon inspecting the switch configuration, the engineer notices the following configuration on the VLAN 10 interfaces:
- switchport mode is set to 'access'
- VLAN 10 is active in the VLAN database
- STP (Spanning Tree Protocol) is enabled
Which of the following could be the cause of the issue?
- A
The VLAN 10 interfaces are configured with an incorrect trunk mode.
- B
The VLAN 10 interfaces are administratively shut down.
- C
VLAN 10 is not allowed on the trunk link to the core switch.
- D
There is a Layer 2 loop causing STP to block the VLAN 10 interfaces.
- E
The VLAN 10 interfaces are configured to use a mismatched native VLAN.
Show answer and explanation
Correct answers: B, D
Explanation
For hosts in VLAN 10 to communicate within the same switch, the VLAN must be active, the interfaces must be in the correct mode, and there should not be any STP-related blocking. In this scenario, administrative shutdown of interfaces or STP blocking due to a Layer 2 loop are the most likely causes of the issue.
- A. Incorrect.
Incorrect. The interfaces are explicitly stated to be in 'access' mode, so trunk mode misconfiguration is not relevant in this scenario.
- B. Correct.
Correct. If the interfaces in VLAN 10 are administratively shut down, communication will fail even though the VLAN is active.
- C. Incorrect.
Incorrect. VLAN 10 communication within the same switch does not depend on trunking to other switches. This would only affect inter-switch communication.
- D. Correct.
Correct. A Layer 2 loop could cause Spanning Tree Protocol to block VLAN 10 interfaces to prevent network instability.
- E. Incorrect.
Incorrect. A mismatched native VLAN would only impact untagged traffic on trunk ports, not the VLAN 10 communication within access interfaces.