200-301 Question 191
Single answerA network administrator is configuring a trunk link between two switches, Switch1 and Switch2, to allow multiple VLANs to communicate across the link. The administrator notices that VLANs are not propagating between the switches. Upon inspecting the configuration, they find the following on Switch1:
interface FastEthernet0/1 switchport mode trunk switchport trunk allowed vlan 10,20
And the following on Switch2:
interface FastEthernet0/1 switchport mode trunk switchport trunk allowed vlan 20,30
What could be the cause of the issue?
- A
The native VLAN is not configured on either switch.
- B
The trunk mode is not correctly set on both switches.
- C
The VLANs allowed on the trunk link do not match between the switches.
- D
The trunk encapsulation type is not specified on both switches.
Show answer and explanation
Correct answer: C
Explanation
The issue arises because the VLANs allowed on the trunk link are not consistent between the two switches. While Switch1 allows VLANs 10 and 20, Switch2 allows VLANs 20 and 30. For VLAN traffic to propagate correctly, the allowed VLANs on the trunk link must be consistent on both switches. Configuring the same set of VLANs on both switches will resolve the issue.
- A. Incorrect.
The native VLAN is not directly related to the issue described, as it does not impact the allowed VLANs on the trunk link.
- B. Incorrect.
The trunk mode is correctly set to ‘switchport mode trunk’ on both switches, so this is not the cause of the issue.
- C. Correct.
The mismatched VLANs allowed on the trunk link (VLAN 10,20 on Switch1 and VLAN 20,30 on Switch2) prevent VLAN traffic from propagating properly.
- D. Incorrect.
Modern switches often use dynamic trunking protocol (DTP) to negotiate trunk encapsulation, and the encapsulation type is not mentioned as an issue in this scenario.