350-401 Question 126
Single answerA network administrator is troubleshooting connectivity issues between two switches connected via an 802.1Q trunk. The administrator notices that VLAN traffic is not passing correctly across the trunk. Upon inspecting the configuration, the following details are found:
- SwitchA has the trunk port configured with 'switchport mode trunk' and the native VLAN set to 1.
- SwitchB has the trunk port configured with 'switchport mode trunk', but the native VLAN is set to 99.
Which step should the administrator take to resolve the issue?
- A
Reconfigure the native VLAN on SwitchB to match the native VLAN on SwitchA.
- B
Disable 802.1Q encapsulation on both trunk ports.
- C
Change the trunk mode on both switches to 'switchport mode access'.
- D
Enable VLAN pruning on the trunk ports.
Show answer and explanation
Correct answer: A
Explanation
In 802.1Q trunking, the native VLAN must match on both sides of a trunk link. If the native VLANs are mismatched, untagged traffic can be misinterpreted, leading to connectivity issues. Reconfiguring the native VLAN on SwitchB to match SwitchA ensures proper communication and resolves the issue.
- A. Correct.
Correct. Both trunk ports must have the same native VLAN configured to avoid traffic misinterpretation and ensure proper VLAN tagging and forwarding.
- B. Incorrect.
Incorrect. Disabling 802.1Q encapsulation would prevent trunking altogether, and VLAN traffic would not pass between the switches.
- C. Incorrect.
Incorrect. Configuring the ports as access mode disables trunking and restricts the port to a single VLAN, which would not resolve the issue.
- D. Incorrect.
Incorrect. VLAN pruning is used to limit unnecessary VLAN traffic on the trunk but does not address mismatched native VLANs, which is the root cause of the issue.