JN0-106 Operational Monitoring and Maintenance Practice Question
A network engineer suspects a hardware issue on an interface. Which command provides the most detailed hardware error counters, including CRC errors, framing errors, and runts?
⚠ Common exam trap
Many exam-takers confuse 'show interfaces detail' with 'show interfaces extensive', assuming 'detail' provides the most granular error counters, but only 'extensive' includes the full hardware error breakdown required for hardware fault diagnosis.
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
✓
show interfaces extensive
The 'show interfaces extensive' command provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command displays per-interface statistics at the physical layer, such as input errors, output errors, and specific error types like frame, runts, giants, and CRC errors, which are essential for diagnosing hardware issues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
show interfaces diagnostics optics
Why it's wrong here
'show interfaces diagnostics optics' is intended for optical interfaces only. It reports digital optical monitoring parameters such as laser bias current, temperature, transmit/receive power, and voltage thresholds from the transceiver. It does not display link-layer error counters like CRC, framing errors, runts, or giants. Therefore, for a suspected hardware issue on a non-optical interface or a data-link-level fault, this command provides no relevant error-counting information.
- ✗
show interfaces detail
Why it's wrong here
'show interfaces detail' presents an abbreviated per-interface view, including aggregate input/output error counters. However, it does not separate errors into granular categories such as CRC, alignment, and runt errors in a way that helps pinpoint hardware degradation. The detail output also omits per-queue statistics and some physical-layer details that become critical for diagnosing faulty transceivers or cabling. For this reason, it is less effective than 'show interfaces extensive' for isolating a hardware issue.
- ✓
show interfaces extensive
Why this is correct
'show interfaces extensive' is the definitive operational command for hardware error analysis on Junos. It outputs each interface's input breakdown, including CRC errors, frame errors, runts, giants, and resource exhaustion, plus output error subcategories like carrier transitions and errors. It also reveals physical-layer state and multiple logical unit statistics, making it possible to correlate errors with transmit/receive activity. When you suspect a hardware fault, this command gives the most complete and structured view of interface health.
- ✗
show log messages
Why it's wrong here
'show log messages' displays event-based system logging, not structured per-interface counters. Interface errors may appear in the log as syslog events, but they are often aggregated, timestamped, and subject to syslog filtering or rate limiting. Additionally, log entries do not provide a real-time or historical numerical breakdown of specific error types for each interface. It is a supplementary tool for contextual events (like link flaps), not a replacement for direct statistical queries.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper 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 JN0-106 exam.