Cybersecurity-Apprentice Network Fundamentals Practice Question
A network security analyst is troubleshooting intermittent packet drops on a high-speed trunk interface connected to a core switch. The interface is configured as Layer 3 with 1 Gbps speed and full duplex. The switch port is also set to 1 Gbps full duplex. However, FCS (Frame Check Sequence) errors are incrementing rapidly. What is the most probable cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Physical layer issues such as damaged cabling, bad SFP transceivers, or electromagnetic interference
Incrementing FCS errors and CRC errors on an Ethernet interface typically indicate physical layer issues such as bad cabling, duplex mismatches (though both set to full), or physical media degradation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
An incorrect Zone Protection Profile flooding threshold
Why it's wrong here
Zone protection thresholds drop packets based on rate-limiting, but do not corrupt Frame Check Sequences (FCS).
- ✓
Physical layer issues such as damaged cabling, bad SFP transceivers, or electromagnetic interference
Why this is correct
FCS errors are generated when frames arrive corrupted at the physical layer, pointing to faulty cabling, connectors, or SFPs.
- ✗
A mismatch in Virtual Router metric values
Why it's wrong here
Virtual router metrics affect path selection in routing tables, not Layer 2 Ethernet frame checksums.
- ✗
Incorrect TCP MSS adjustment on the Layer 3 interface
Why it's wrong here
MSS adjustment modifies TCP payload sizes to prevent fragmentation; it does not cause Layer 2 FCS corruption.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Palo Alto Networks exam blueprint
This Cybersecurity-Apprentice practice question is part of Courseiva's free Palo Alto Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the Cybersecurity-Apprentice exam.