350-401 Question #1289: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. An engineer is troubleshooting a trunk link failure between Switch-1 and Switch-2. Which action will resolve this issue?

Options

• AConfigure the same native VLAN on both interfaces
• BConfigure the same spanning tree mode on both switches
• CSet the same port speed on both switches
• DConfigure the same trunk mode on both switches

Explanation

A common cause of trunk link failure is a native VLAN mismatch between the two switches, which causes the trunk to become non-operational by blocking traffic or placing the port in an err-disabled state.

Common mistakes.

• B. While it is generally best practice to use consistent spanning tree modes, a mismatch in STP mode does not typically cause a trunk link to fail or become non-operational in the same direct manner as a native VLAN mismatch.
• C. A port speed mismatch would prevent the physical link from establishing or cause it to operate poorly, which is a physical layer issue rather than a specific trunking protocol failure.
• D. A trunk mode mismatch, such as one side being access mode while the other tries to trunk, would prevent the trunk from forming in the first place; however, a native VLAN mismatch can cause an already established or intended trunk to fail or be blocked.

Concept tested. Cisco trunking troubleshooting (native VLAN mismatch)

Reference. https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10559-10.html

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