CCNP Network Assurance Practice Question
A network administrator is examining the output of the show interfaces command on a switch and notices a high number of CRC errors on a Gigabit Ethernet port. What is the most likely cause of these errors?
⚠ Common exam trap
The trap here is attributing CRC errors to duplex mismatch, when in fact CRC errors are more directly indicative of physical layer problems such as bad cabling.
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
✓
Cable interference or damage
CRC errors are a physical layer symptom indicating frame corruption. The most common cause is cable interference, damage, or faulty connectors. While duplex mismatch can cause errors, it typically manifests as late collisions and FCS errors, not CRC errors. Therefore, cable issues are the most likely cause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Duplex mismatch
Why it's wrong here
A duplex mismatch typically causes late collisions and FCS errors, not CRC errors. CRC errors indicate frame corruption, often due to physical layer issues. While duplex mismatch can cause errors, the specific CRC error counter points more directly to cabling or hardware problems.
- ✗
VLAN mismatch
Why it's wrong here
A VLAN mismatch on a trunk link would cause connectivity issues between VLANs but would not generate CRC errors on a physical interface. CRC errors are a layer 1 symptom, while VLAN mismatches are layer 2 configuration issues.
- ✗
Speed mismatch
Why it's wrong here
A speed mismatch would prevent the link from coming up or cause severe performance issues, but it would not typically generate CRC errors. Speed mismatches usually result in link down or high error rates due to framing issues, not CRC errors specifically.
- ✓
Cable interference or damage
Why this is correct
CRC errors indicate that frames are being corrupted during transmission, which is commonly caused by cable interference, damage, or poor quality cabling. The CRC checksum fails when bits are altered, so the issue is likely at the physical layer. This is the most probable cause.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 practice question is part of Courseiva's free Cisco 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 350-401 exam.