Quick Answer
The answer is the commit synchronize command. This is the correct choice because in a dual Routing Engine system, the candidate configuration must be applied to both the master and backup RE simultaneously to maintain consistency; the commit synchronize command achieves this by committing the configuration on both engines at once, ensuring that if a failover occurs, the backup RE has an identical operational state. On the JNCIA-Junos exam, this concept tests your understanding of high-availability features and dual-RE architecture, often appearing in questions that contrast commit synchronize with a standard commit, which only affects the local RE. A common trap is confusing commit synchronize with commit check or commit confirmed, so remember that synchronize is specifically for dual-RE environments. For a memory tip, think of the word “sync” as in synchronize—it forces both engines to sing the same configuration song.
This JNCIA-JUNOS practice question tests your understanding of user interfaces. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A user wants to ensure that a configuration change is applied across both Routing Engines in a dual-RE system. Which command must be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
commit and-quit
Why wrong: Commits and exits configuration mode but does not synchronize.
commit confirmed
Why wrong: Commits with automatic rollback, not synchronization.
commit full
Why wrong: Not a valid Junos command.
commit synchronize
Correctly applies the commit to both Routing Engines.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
commit synchronize
Option D is correct because the 'commit synchronize' command applies the candidate configuration to both Routing Engines simultaneously in a dual-RE system. This ensures configuration consistency across the master and backup RE, which is critical for high availability and seamless failover in Junos.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
commit and-quit
Why it's wrong here
Commits and exits configuration mode but does not synchronize.
commit confirmed
Why it's wrong here
Commits with automatic rollback, not synchronization.
commit full
Why it's wrong here
Not a valid Junos command.
commit synchronize
Why this is correct
Correctly applies the commit to both Routing Engines.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse 'commit synchronize' with 'commit full' or 'commit confirmed', assuming any commit command applies to both REs, but only 'commit synchronize' explicitly ensures dual-RE consistency.
Trap categories for this question
Command / output trap
Not a valid Junos command.
Detailed technical explanation
In Junos, the 'commit synchronize' command triggers a commit on the master RE and then automatically copies the committed configuration to the backup RE, where it is also committed. This is essential in chassis clusters or dual-RE systems (e.g., EX4200 virtual chassis or MX routers with redundant REs) to prevent configuration drift. Without synchronization, a failover could result in the backup RE running an outdated configuration, causing service disruption.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
User Interfaces — study guide chapter
Learn the concepts, then practise the questions
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FAQ
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
The correct answer is: commit synchronize — Option D is correct because the 'commit synchronize' command applies the candidate configuration to both Routing Engines simultaneously in a dual-RE system. This ensures configuration consistency across the master and backup RE, which is critical for high availability and seamless failover in Junos.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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.
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