This JNCIA-JUNOS practice question tests your understanding of user interfaces. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 configuration interfaces ge-0/0/0
unit 0 {
family inet {
address 10.0.0.1/24;
}
family inet6 {
address 2001:db8::1/64;
}
}
user@router> show interfaces terse ge-0/0/0
Interface Admin Link Proto Local Remote
ge-0/0/0 up up inet 10.0.0.1/24
inet6 2001:db8::1/64
Refer to the exhibit. An engineer configures a new IPv6 address on ge-0/0/0 unit 0 by entering the following commands in configuration mode:
set interfaces ge-0/0/0 unit 0 family inet6 address 2001:db8::2/64
commit
After the commit, the engineer runs 'show interfaces terse ge-0/0/0' and sees only the two original addresses. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Refer to the exhibit.
user@router> show configuration interfaces ge-0/0/0
unit 0 {
family inet {
address 10.0.0.1/24;
}
family inet6 {
address 2001:db8::1/64;
}
}
user@router> show interfaces terse ge-0/0/0
Interface Admin Link Proto Local Remote
ge-0/0/0 up up inet 10.0.0.1/24
inet6 2001:db8::1/64
A
The engineer used 'commit' instead of 'commit confirmed'.
Why wrong: A standard commit is sufficient to apply changes.
B
The engineer did not enter configuration mode before running the 'set' command.
'set' is a configuration mode command; in operational mode it would be rejected.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The engineer did not enter configuration mode before running the 'set' command.
Option B is correct because the engineer likely ran the 'set' command from operational mode (e.g., at the '>' prompt) rather than from configuration mode (e.g., at the '#' prompt). In Junos, 'set' commands only take effect when entered in configuration mode; if entered in operational mode, they are silently ignored or produce an error, and the configuration is not modified. Since the engineer saw no new address after commit, the 'set' command was never applied to the candidate configuration.
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.
✗
The engineer used 'commit' instead of 'commit confirmed'.
Why it's wrong here
A standard commit is sufficient to apply changes.
✓
The engineer did not enter configuration mode before running the 'set' command.
Why this is correct
'set' is a configuration mode command; in operational mode it would be rejected.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Junos only allows one IPv6 address per interface.
Why it's wrong here
Junos supports multiple IPv6 addresses.
✗
The 'set' command requires the 'add' keyword to add a second address.
Why it's wrong here
'set' is used to add or change configuration; no 'add' keyword needed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates accustomed to Cisco IOS may assume a 'set' command entered at any prompt modifies the running configuration, but Junos requires explicit entry into configuration mode (via 'configure' or 'edit') for such commands to take effect.
Trap categories for this question
Keyword trap
'set' is used to add or change configuration; no 'add' keyword needed.
Detailed technical explanation
How to think about this question
Junos separates operational mode (for monitoring and troubleshooting) from configuration mode (for editing the candidate configuration). Commands like 'set interfaces ge-0/0/0 unit 0 family inet6 address 2001:db8::2/64' are only valid in configuration mode; in operational mode, they are not recognized as configuration commands and produce no change. This strict mode separation is fundamental to Junos and differs from Cisco IOS, where many configuration commands can be entered from privileged EXEC mode.
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.
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The engineer did not enter configuration mode before running the 'set' command. — Option B is correct because the engineer likely ran the 'set' command from operational mode (e.g., at the '>' prompt) rather than from configuration mode (e.g., at the '#' prompt). In Junos, 'set' commands only take effect when entered in configuration mode; if entered in operational mode, they are silently ignored or produce an error, and the configuration is not modified. Since the engineer saw no new address after commit, the 'set' command was never applied to the candidate configuration.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.