The answer is ge-0/0/1 only, because its 'Physical link is Down' status directly indicates a Layer 1 issue, such as a disconnected cable, faulty transceiver, or a powered-down remote device. In Junos, physical link down detection relies on the interface's carrier signal; when the hardware layer fails to detect this signal, the interface reports 'Down' at the physical level, while the other interfaces showing 'Up' confirm they have no such physical layer problem. On the JNCIA-Junos exam, this concept tests your ability to distinguish between physical and logical interface states—a common trap is confusing 'Physical link is Down' with protocol-level failures like 'Down' in the protocol state. Remember that physical link status is always the first thing to check when troubleshooting connectivity; a quick memory tip is 'Layer 1 first'—if the physical link is down, no higher-layer protocols can function, so always verify cables and transceivers before moving up the stack.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
user@router> show interfaces terse | match ge-0/0/
ge-0/0/0 up up inet 10.0.0.1/30
ge-0/0/1 up down inet 10.0.1.1/30
ge-0/0/2 down down
ge-0/0/3 up up inet 10.0.2.1/30
inet6 fe80::/64
Refer to the exhibit. Which interface(s) have a physical layer issue?
Refer to the exhibit.
user@router> show interfaces terse | match ge-0/0/
ge-0/0/0 up up inet 10.0.0.1/30
ge-0/0/1 up down inet 10.0.1.1/30
ge-0/0/2 down down
ge-0/0/3 up up inet 10.0.2.1/30
inet6 fe80::/64
A
ge-0/0/1 only
ge-0/0/1 has link down while admin up, indicating physical issue.
B
ge-0/0/0 only
Why wrong: ge-0/0/0 has both admin and link up, so no issue.
C
ge-0/0/0 and ge-0/0/2
Why wrong: Neither has physical issue as explained.
D
ge-0/0/2 only
Why wrong: ge-0/0/2 is administratively down, so not a physical issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ge-0/0/1 only
The 'Physical link is Down' status on ge-0/0/1 indicates a Layer 1 issue, such as a disconnected cable, faulty transceiver, or powered-down remote device. The other interfaces show 'Up' physical status, confirming they have no physical layer problem.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
ge-0/0/1 only
Why this is correct
ge-0/0/1 has link down while admin up, indicating physical issue.
Related concept
Read the scenario before looking for a memorised answer.
✗
ge-0/0/0 only
Why it's wrong here
ge-0/0/0 has both admin and link up, so no issue.
✗
ge-0/0/0 and ge-0/0/2
Why it's wrong here
Neither has physical issue as explained.
✗
ge-0/0/2 only
Why it's wrong here
ge-0/0/2 is administratively down, so not a physical issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse 'Physical link is Down' with an administrative 'down' state, but the output clearly shows 'up' in the admin column, so the issue is purely physical layer, not configuration-based.
Detailed technical explanation
How to think about this question
The 'Physical link' status in 'show interfaces terse' reflects the carrier detect signal from the transceiver or media adapter. A 'Down' state can result from cable faults, speed/duplex mismatches, or remote device shutdown, and is independent of the administrative 'Admin' state. In Junos, 'show interfaces diagnostics optics' can further isolate physical layer issues like low optical power or high bit error rates.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ge-0/0/1 only — The 'Physical link is Down' status on ge-0/0/1 indicates a Layer 1 issue, such as a disconnected cable, faulty transceiver, or powered-down remote device. The other interfaces show 'Up' physical status, confirming they have no physical layer problem.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This JNCIA-JUNOS 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 JNCIA-JUNOS exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.