350-401 Question 128
Single answerA network engineer is troubleshooting a connectivity issue between two switches, SW1 and SW2. Both switches are connected via a trunk link, and VLAN traffic is not passing between them. Upon inspection, the following configurations are identified:
- SW1 interface configuration: switchport trunk encapsulation dot1q switchport mode trunk
- SW2 interface configuration: switchport trunk encapsulation negotiate switchport mode trunk
What could be the cause of the issue?
- A
SW1 and SW2 are configured with different VLANs allowed on the trunk.
- B
SW2 is set to dynamically negotiate the trunk encapsulation, which is incompatible with SW1's static configuration.
- C
The native VLAN on SW1 and SW2 is mismatched, causing VLAN traffic to drop.
- D
The trunk link between SW1 and SW2 is administratively shut down.
Show answer and explanation
Correct answer: B
Explanation
In this scenario, SW1 is statically configured to use 802.1Q encapsulation, while SW2 is set to negotiate the encapsulation dynamically. Since SW1 does not allow for negotiation, SW2 fails to establish a compatible trunk configuration. To resolve this issue, the encapsulation method on SW2 should be manually set to dot1q to match SW1's configuration. This ensures that both switches are using a compatible trunk encapsulation method.
- A. Incorrect.
While VLAN mismatches can cause issues, this is not the specific problem in this scenario. The issue is related to the encapsulation method, not the allowed VLANs.
- B. Correct.
SW2 is configured to negotiate the trunk encapsulation dynamically using the 'negotiate' keyword, but SW1 is statically set to use 802.1Q (dot1q). This mismatch prevents the trunk from forming properly, as the dynamic negotiation fails.
- C. Incorrect.
A native VLAN mismatch can cause connectivity issues such as untagged traffic being dropped, but it would not completely prevent VLAN traffic from passing through the trunk. The issue here is related to trunk encapsulation.
- D. Incorrect.
If the trunk link were administratively shut down, the interfaces would not be operational. However, the question does not indicate that the interfaces are down, so this is not the cause.