Quick Answer
The answer is the `commit synchronize` command. This is correct because in a dual Routing Engine chassis, the Junos operating system maintains separate candidate configurations on each RE; the `commit synchronize` command forces the master RE to first commit its configuration, then automatically copy and commit that exact configuration to the backup RE, ensuring both Routing Engines run identical active configurations immediately. On the JNCIA-Junos exam, this concept tests your understanding of high-availability chassis operations and the distinction between a normal `commit` (which only affects the local RE) and `commit synchronize` (which propagates the change). A common trap is assuming a standard `commit` on the master will automatically sync to the backup—it will not. Remember the memory tip: “Sync to stay in sync”—if you need both REs aligned, always use `commit synchronize` rather than a plain commit.
This JNCIA-JUNOS practice question tests your understanding of junos configuration basics. 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.
In a dual Routing Engine (RE) setup, an engineer commits a configuration change that should be applied to both REs synchronously. What is the correct command to ensure both REs receive the same configuration immediately?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
commit confirmed
Why wrong: 'commit confirmed' does not synchronize with the other RE.
commit check synchronize
Why wrong: 'commit check synchronize' validates syntax on both REs but does not commit.
commit and-quit
Why wrong: 'commit and-quit' commits and exits configuration mode but does not synchronize.
commit synchronize
'commit synchronize' commits the configuration on both Routing Engines simultaneously.
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 commits the configuration on the master Routing Engine and then automatically copies and commits the same configuration to the backup RE, ensuring both REs have identical active configurations immediately. This is the standard Junos method for synchronizing configurations in a dual-RE chassis.
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 confirmed
Why it's wrong here
'commit confirmed' does not synchronize with the other RE.
commit check synchronize
Why it's wrong here
'commit check synchronize' validates syntax on both REs but does not commit.
commit and-quit
Why it's wrong here
'commit and-quit' commits and exits configuration mode but does not synchronize.
commit synchronize
Why this is correct
'commit synchronize' commits the configuration on both Routing Engines simultaneously.
Clue confirmation
The clue word "immediately / without restart" 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 confuse 'commit synchronize' with 'commit check' or 'commit confirmed', not realizing that only 'commit synchronize' explicitly pushes the configuration to the backup RE in a dual-RE setup.
Detailed technical explanation
When 'commit synchronize' is issued, the master RE first validates and commits the configuration locally, then uses the Junos kernel replication mechanism to push the committed configuration to the backup RE, which performs its own commit. In a graceful Routing Engine switchover (GRES) scenario, this ensures both REs have identical operational configurations, preventing traffic disruption during failover. The command is equivalent to running 'commit' on the master followed by 'request routing-engine login backup' and 'commit' on the backup, but is atomic and simpler.
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.
Junos Configuration Basics — study guide chapter
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FAQ
Junos Configuration Basics — This question tests Junos Configuration Basics — Read the scenario before looking for a memorised answer..
The correct answer is: commit synchronize — Option D is correct because the 'commit synchronize' command commits the configuration on the master Routing Engine and then automatically copies and commits the same configuration to the backup RE, ensuring both REs have identical active configurations immediately. This is the standard Junos method for synchronizing configurations in a dual-RE chassis.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "immediately / without restart". Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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