JN0-106 Junos Configuration Basics Practice Question
A company has two Juniper routers in a high-availability cluster with dual Routing Engines. The administrator performs a commit on the primary RE. What is the effect of using the 'commit synchronize' command?
⚠ Common exam trap
A common mix-up: candidates confuse 'commit synchronize' with 'commit check' or assume it only affects one RE, failing to recognize that Juniper's high-availability design requires explicit synchronization to maintain configuration consistency across both Routing Engines.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It commits the configuration on both Routing Engines simultaneously.
The 'commit synchronize' command on Juniper routers with dual Routing Engines ensures that the configuration is committed on both the primary and backup REs simultaneously. This is critical for maintaining configuration consistency in a high-availability cluster, as it prevents a split-brain scenario where the backup RE has a different active configuration than the primary. The command performs a full commit (including validation and activation) on both REs, not just a check.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It performs a commit check on both REs but does not activate the config.
Why it's wrong here
A commit check is a dry-run validation that examines the candidate configuration for syntax errors, semantic problems, and other inconsistencies without applying it to the active configuration. In a dual-RE high-availability cluster, you might run 'commit check' (or 'commit check synchronize') to preview the change, but it never activates the configuration on either RE. This is in contrast to the required 'commit synchronize', which loads and activates the configuration on both Routing Engines, making it the actual commit operation.
- ✓
It commits the configuration on both Routing Engines simultaneously.
Why this is correct
The correct behavior is 'commit synchronize', a Junos command that loads and activates the candidate configuration on both the primary and backup Routing Engines simultaneously, ensuring they operate with identical active configurations. This is critical for high-availability clusters because it prevents config drift, so failover to the backup will use the same settings and policies as the primary. The simultaneous commit minimizes the window of inconsistency and is the standard method for configuring both REs in one operation.
- ✗
It commits the configuration only on the primary RE.
Why it's wrong here
A plain 'commit' executed on the primary Routing Engine without the 'synchronize' option applies the candidate configuration only to that RE, leaving the backup Running the previous configuration. This creates a mismatch between the two REs, which is dangerous in a high-availability cluster because if the primary fails, the backup will come online with stale or incompatible settings. High-availability clusters mandate that both REs share the same configuration, so a non-synchronized commit is insufficient and violates the dual-RE consistency requirement.
- ✗
It commits the configuration only on the backup RE.
Why it's wrong here
Committing only on the backup Routing Engine is non-standard and particularly flawed: it forces the backup to accept a configuration that the primary never validated or activated, while the primary continues running its old configuration. Even if you execute a commit from the backup RE (which may be possible in some Junos configurations), the primary's configuration remains untouched, resulting in two divergent active configurations. The proper operation for a cluster is always a synchronized commit that writes and activates the same configuration on both REs, ensuring cluster-wide consistency.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 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 JN0-106 exam.