The answer is ge-0/0/1 because the output shows 'Physical link is Down' and 'Device present: No', which together confirm a physical layer connectivity problem. On Juniper devices, the 'Physical link' field directly reports Layer 1 status, and when it is Down, the interface cannot pass any traffic regardless of higher-layer configurations. The 'Device present' field being No further indicates that no transceiver or cable is detected, isolating the fault to the physical medium rather than a protocol or configuration issue. On the JNCIA-Junos exam, this concept tests your ability to interpret the output of 'show interfaces terse' or 'show interfaces extensive' and distinguish between Layer 1, Layer 2, and Layer 3 problems. A common trap is confusing an administratively down interface with a physical link down—remember that 'Physical link is Down' always points to a cable, transceiver, or hardware fault, not a configuration command. Memory tip: If the link is down and no device is present, think "no hardware, no handshake."
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
Output of 'show interfaces terse':
Interface Admin Link Proto Local Remote
ge-0/0/0 up up inet 192.168.1.1/24
ge-0/0/1 up down inet
ge-0/0/2 down down
ge-0/0/3 up up inet 10.0.0.1/30
lo0 up up inet 127.0.0.1
Refer to the exhibit. Which interface has a physical layer connectivity problem?
Output of 'show interfaces terse':
Interface Admin Link Proto Local Remote
ge-0/0/0 up up inet 192.168.1.1/24
ge-0/0/1 up down inet
ge-0/0/2 down down
ge-0/0/3 up up inet 10.0.0.1/30
lo0 up up inet 127.0.0.1
A
ge-0/0/2
Why wrong: ge-0/0/2 is administratively down, so it is expected to have the link down. This is not a physical problem; it is a configuration state.
B
ge-0/0/0
Why wrong: ge-0/0/0 is administratively up and the link is up, indicating no physical problem.
C
ge-0/0/3
Why wrong: ge-0/0/3 is administratively up and link is up, so no physical problem.
D
ge-0/0/1
ge-0/0/1 is administratively up but the link is down. This indicates a physical layer issue, such as a disconnected cable, faulty transceiver, or peer problem.
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
Interface ge-0/0/1 shows 'Physical link is Down' in the output, which directly indicates a physical layer connectivity problem. The 'Device present' field is also 'No', confirming that no transceiver or cable is detected, which is a Layer 1 issue.
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-0/0/2
Why it's wrong here
ge-0/0/2 is administratively down, so it is expected to have the link down. This is not a physical problem; it is a configuration state.
✗
ge-0/0/0
Why it's wrong here
ge-0/0/0 is administratively up and the link is up, indicating no physical problem.
✗
ge-0/0/3
Why it's wrong here
ge-0/0/3 is administratively up and link is up, so no physical problem.
✓
ge-0/0/1
Why this is correct
ge-0/0/1 is administratively up but the link is down. This indicates a physical layer issue, such as a disconnected cable, faulty transceiver, or peer problem.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on the 'Admin' status (up/down) rather than the 'Physical link' status, mistakenly assuming an administratively down interface is a physical layer problem, when in fact the physical layer issue is indicated by the link state being down regardless of administrative configuration.
Detailed technical explanation
How to think about this question
The 'show interfaces terse' command displays the administrative and operational status of interfaces, but for physical layer diagnostics, 'show interfaces <name>' or 'show interfaces diagnostics optics' provides detailed Layer 1 information such as link state, media type, and transceiver presence. In Junos, a 'Physical link is Down' state can result from a faulty cable, disabled port, or missing SFP module, and the 'Device present' field specifically indicates whether the hardware transceiver is detected.
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 — Interface ge-0/0/1 shows 'Physical link is Down' in the output, which directly indicates a physical layer connectivity problem. The 'Device present' field is also 'No', confirming that no transceiver or cable is detected, which is a Layer 1 issue.
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.
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