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N10-009 · Question #376

N10-009 Question #376: Real Exam Question with Answer & Explanation

The correct answer is D: Native VLAN mismatch. A native VLAN mismatch occurs when two trunk ports connected to each other have different native VLANs configured, which can cause traffic from both native VLANs to flood each other, potentially leading to spanning tree issues or network loops that disrupt connectivity for many u

Submitted by saadiq_pk· Mar 6, 2026Network Troubleshooting

Question

After a networking intern plugged in a switch, a significant number of users in a building lost connectivity. Which of the following is the most likely root cause?

Options

  • AVTP update
  • BPort security issue
  • CLLDP misconfiguration
  • DNative VLAN mismatch

Explanation

A native VLAN mismatch occurs when two trunk ports connected to each other have different native VLANs configured, which can cause traffic from both native VLANs to flood each other, potentially leading to spanning tree issues or network loops that disrupt connectivity for many users.

Common mistakes.

  • A. A VTP (VLAN Trunking Protocol) update, while it can cause issues if misconfigured, is less likely to immediately take down a significant number of users simply by plugging in a switch, especially if the new switch is not yet configured to participate in VTP or has a different domain/password.
  • B. A port security issue typically restricts access for specific devices on a single port or group of ports, not causing widespread connectivity loss across an entire building.
  • C. An LLDP (Link Layer Discovery Protocol) misconfiguration would primarily affect the ability of devices to discover and identify neighbors, not directly cause a widespread loss of network connectivity.

Concept tested. Common switch misconfigurations (Native VLAN mismatch)

Reference. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_25_see/configuration/guide/sw_clan.pdf

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