Which command is used on a Cisco switch to display trunking information and verify that an interface is operating as a trunk?
Correct Answer: A
Detailed Explanation: In Cisco switching environments, trunking is a method that allows multiple VLANs to traverse a single physical link between switches. To verify trunk operation and diagnose trunk-related issues, network administrators rely on specific Cisco IOS commands. The command “show interface trunk” is the primary command used for this purpose. When you issue the “show interface trunk” command, the switch displays detailed information about all interfaces configured as trunks. This information typically includes the following: Trunking Mode: Whether the port is set to trunk, dynamic desirable, or dynamic auto. Encapsulation Type: The type of VLAN tagging being used (typically IEEE 802.1Q). Allowed VLANs: The list of VLANs that are allowed to pass over the trunk link. Active VLANs: VLANs that are currently active on the trunk. Native VLAN: The VLAN that is untagged on the trunk (by default, VLAN 1 unless configured otherwise). This command provides a snapshot of the trunk configuration, allowing administrators to verify that the correct VLANs are being transmitted and that the trunk link is functioning as expected. Alternative Commands and Their Uses: show interfaces switchport (Option C): This command also provides valuable information about interface modes, including whether an interface is operating as an access or trunk port. However, it provides more general switchport details rather than a focused view of trunk status. show running-config trunk (Option B): There is no such command in Cisco IOS; trunk configurations are part of the overall interface configuration. show port-channel summary (Option D): This command is used for EtherChannel (link aggregation) verification and is not specific to trunk verification. Importance of Verifying Trunk Operation: Trunk links are critical for carrying multiple VLANs across switches, which is a core part of modern network segmentation and design. Incorrect trunk configurations can lead to issues such as VLAN leakage (where traffic from one VLAN appears on another), dropped frames, or even complete loss of connectivity between switches. Regular verification with “show interface trunk” helps ensure that trunks are correctly configured and that the expected VLANs are allowed on the link. Troubleshooting Scenarios: For instance, if a network segment suddenly experiences connectivity problems between departments that reside on different VLANs, checking the trunk status using “show interface trunk” can reveal whether the trunk link is misconfigured or if a change (such as an accidental removal of allowed VLANs) has occurred. Conclusion: The “show interface trunk” command is the most effective and direct method for verifying trunk configuration on a Cisco switch. It provides administrators with comprehensive details on trunk status, including allowed VLANs, active VLANs, and trunking modes. Mastery of this command is crucial for maintaining the health and performance of VLAN trunk links within enterprise networks.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.