350-401 Question 123
Single answerYou are configuring a Layer 2 switch in your company's network. A colleague reports that traffic from certain VLANs is not being forwarded across the trunk link between two switches. Upon investigation, you find that the trunk link is configured to allow only specific VLANs. What command should be used to ensure all VLANs are allowed across the trunk link?
- A
switchport trunk allowed vlan all
- B
switchport trunk allowed vlan add all
- C
switchport trunk allowed vlan 1-4094
- D
switchport mode trunk
Show answer and explanation
Correct answer: C
Explanation
To ensure that all VLANs are allowed across a trunk link, the command 'switchport trunk allowed vlan 1-4094' must be used. This explicitly configures the trunk to allow all VLAN IDs in the valid range (1-4094). While 'switchport mode trunk' enables trunking on the interface, it does not affect VLAN filtering. Understanding the proper configuration of trunk links is essential for Layer 2 network operations, especially in VLAN environments.
- A. Incorrect.
This command is invalid. There is no 'all' keyword to allow all VLANs on a trunk in Cisco IOS.
- B. Incorrect.
This command is incorrect. The 'add all' statement is not a valid syntax in Cisco IOS.
- C. Correct.
This is the correct command to allow all VLANs (1-4094) on the trunk link.
- D. Incorrect.
While this command configures the interface as a trunk, it does not modify which VLANs are allowed on the trunk.