CompTIA Network+ OSI Model Practice Questions: Troubleshooting

5 free, exam-style CompTIA Network+ OSI Model (N10-009) practice questions covering Troubleshooting. Each question shows the correct answer and a clear explanation. Ready for the real thing? Take the full timed quiz below.

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Q1. Which OSI layer is affected when a cable is unplugged?

A.Physical layer✓ Correct
B.Application layer
C.Presentation layer
D.Session layer

Explanation: A disconnected cable is a Layer 1 physical connectivity problem.

Q2. Which OSI layer is affected when a switch port is in the wrong VLAN?

A.Data Link layer✓ Correct
B.Presentation layer
C.Session layer
D.Application layer

Explanation: VLAN membership is a Layer 2 switching configuration issue.

Q3. Which OSI layer is affected when a host has the wrong default gateway?

A.Network layer✓ Correct
B.Physical layer
C.Presentation layer
D.Session layer

Explanation: The default gateway is used for Layer 3 routing to remote networks.

Q4. Which OSI layer is affected when a firewall blocks TCP port 443?

A.Transport layer✓ Correct
B.Physical layer
C.Data Link layer only
D.Presentation layer only

Explanation: Filtering by TCP port is a Transport layer control, even when applied by higher-layer firewalls.

Q5. Which OSI layer is affected when DNS resolves the wrong hostname target?

A.Application layer✓ Correct
B.Physical layer
C.Data Link layer
D.Transport layer only

Explanation: DNS is an Application layer service that maps names to addresses.