200-301 Question 195
Single answerA network administrator is configuring VLANs on a switch using 802.1Q trunking. The administrator notices that devices in VLAN 20 on Switch A cannot communicate with devices in VLAN 20 on Switch B. Both switches are connected via a trunk port. Which of the following could be the cause of the issue?
- A
The native VLAN is mismatched on the trunk ports of both switches.
- B
The VLAN 20 is not allowed on the trunk link between the switches.
- C
802.1Q encapsulation is not enabled on the trunk link between switches.
- D
The devices in VLAN 20 have incorrect IP addresses configured.
Show answer and explanation
Correct answer: B
Explanation
For devices in VLAN 20 to communicate across switches, VLAN 20 must be allowed on the trunk link. If it is not allowed, 802.1Q will not tag or forward traffic for VLAN 20 across the trunk, resulting in communication failure.
- A. Incorrect.
A native VLAN mismatch typically causes untagged traffic to be misinterpreted, leading to potential issues with the native VLAN but not directly with tagged VLANs like VLAN 20.
- B. Correct.
VLANs must be explicitly allowed on the trunk link for traffic to pass between switches. If VLAN 20 is not allowed, devices in VLAN 20 will not communicate across the trunk.
- C. Incorrect.
802.1Q encapsulation is usually enabled by default when the trunk is configured. If it were not enabled, no VLAN traffic would pass through the trunk, not just VLAN 20.
- D. Incorrect.
Incorrect IP address configuration on devices in VLAN 20 would prevent communication but would not be related to the 802.1Q trunk configuration.