N10-009 Network Troubleshooting Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  show vlan brief

  Why it's wrong here

  The `show vlan brief` command displays a summary of all configured VLANs on the switch, including their names and the access ports assigned to them. While useful for verifying VLAN existence and port assignments, it does not provide any information about trunk link configurations, such as which VLANs are allowed or disallowed on a specific trunk interface. Therefore, it cannot directly diagnose why a particular VLAN might not be communicating across a trunk.

  When this WOULD be correct

  This command would be correct if the question asked: 'A network administrator needs to verify which VLANs are configured on a switch and which ports are assigned to each VLAN.'

• ✓

  show interfaces trunk

  Why this is correct

  This command is the most effective for troubleshooting VLAN communication issues over a trunk link because it provides a comprehensive overview of the trunk's operational status. It explicitly lists the allowed VLANs on the trunk interface, the native VLAN, and the trunking encapsulation type (e.g., 802.1Q). By checking the "Vlans allowed on trunk" output, an administrator can quickly determine if the specific VLAN experiencing communication problems (e.g., VLAN 20) is permitted to traverse the link.

• ✗

  show running-config interface

  Why it's wrong here

  The `show running-config interface <interface-id>` command displays the specific configuration commands applied to a particular interface from the active running configuration. While it would show explicitly configured `switchport trunk allowed vlan` statements, it might not reveal the *effective* allowed VLAN list if no explicit configuration exists (which defaults to all VLANs). More importantly, it doesn't show the dynamic operational status, such as whether the trunk has actually formed or if there are negotiation issues, making `show interfaces trunk` a more complete diagnostic tool.

  When this WOULD be correct

  This command would be correct if the question asked to verify the configured VLAN settings on a specific interface, such as checking if an access port is assigned to the correct VLAN or if trunk encapsulation is set correctly.

• ✗

  show mac address-table

  Why it's wrong here

  The `show mac address-table` command displays the switch's MAC address table, which maps MAC addresses to specific interfaces and VLANs. This table is crucial for understanding how the switch forwards frames to known destinations. However, it provides no information about the configuration or operational status of trunk links or the VLANs allowed to traverse them, making it irrelevant for diagnosing issues related to VLAN communication across inter-switch trunks.

  When this WOULD be correct

  This command would be correct when troubleshooting MAC address learning issues, such as verifying if a specific MAC address is learned on the correct port or checking for MAC address flapping between ports.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”