Cisco Certified Network Associate (CCNA) Practice Exam

How do you configure allowed VLANs on a trunk interface?

1. (config-if)#switchport trunk allowed vlan VLAN NUMBER

2. (config)#trunk interface INTERFACE

3. (config-if)#enable trunking

4. (config)#interface INTERFACE

The correct answer is: (config-if)#switchport trunk allowed vlan VLAN NUMBER

To configure allowed VLANs on a trunk interface, the appropriate command is to specify which VLANs are permitted to pass through that trunk link. The command format (config-if)#switchport trunk allowed vlan VLAN NUMBER allows the network administrator to define a specific VLAN or a range of VLANs that can traverse the trunk. This is critical for maintaining network efficiency and ensuring that only designated traffic flows across the trunk link. When a switchport is configured as a trunk, it can carry traffic for multiple VLANs. By using this command, administrators have granular control over the VLANs that are allowed to send and receive frames on the trunk. This enhances security and reduces unnecessary broadcast traffic on the network. The other options do not effectively achieve the goal of configuring allowed VLANs. For instance, simply entering (config)#trunk interface INTERFACE does not provide any commands related to VLAN configuration. Similarly, (config-if)#enable trunking lacks the necessary specificity to control which VLANs are allowed on a trunk. The command (config)#interface INTERFACE simply begins the interface configuration mode but does not directly relate to VLANs or trunking. Thus, focusing on the switchport command specifically designed for this purpose is essential for proper trunk configuration.