JN0-106 Junos OS Fundamentals Practice Question
A network engineer made several configuration changes on a Juniper QFX switch to implement new VLANs. After committing the changes, the engineer realized that the new configuration caused a critical loss of connectivity to the management network. The engineer needs to revert to the previous configuration that was working. The switch is still accessible via the console port, and the engineer has privilege level access. The previous configuration was committed two commits ago, and the current active configuration is the problematic one. Which action should the engineer take to restore the previous working configuration?
⚠ Common exam trap
It's easy for candidates to confuse the rollback numbering: candidates often think 'rollback 0' reverts to a previous configuration, but it actually refers to the current active configuration, while 'rollback 1' is needed to go back one commit (the previous working state).
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
✓
Execute 'rollback 2' followed by 'commit'.
The working configuration was committed two commits ago. The 'rollback 2' command loads the configuration from two commits prior into the candidate configuration. After that, 'commit' makes it active, restoring connectivity. Note that 'rollback 1' would load the intermediate commit, which is also problematic, and 'rollback 0' refers to the current active configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use 'load override /config/juniper.conf.1.gz' followed by 'commit'.
Why it's wrong here
load override /config/juniper.conf.1.gz replaces the entire candidate configuration with the file from one commit prior. The filenames are zero-indexed relative to the current state: juniper.conf.0.gz is the active config, juniper.conf.1.gz is one commit back, and juniper.conf.2.gz is two commits back. Since the problem began two commits ago, this file still contains the unwanted changes, so this command would fail to solve the issue.
- ✗
Use 'delete system' to remove all configuration and then commit.
Why it's wrong here
delete system removes the entire system hierarchy, including critical settings such as hostname, root-authentication, and management interface configurations. This would leave the device without basic administrative access or authentication, and is far too excessive for correcting a specific configuration error. It also does not restore a previous committed state; it simply blanks part of the candidate and commits, which is dangerous and not a recovery method.
- ✗
Execute 'rollback 0' followed by 'commit'.
Why it's wrong here
rollback 0 loads the candidate configuration from the current active (last committed) configuration. Because the problematic changes were already committed, this restores exactly the same invalid state. Committing again simply reaffirms those changes and does not undo anything. To truly revert, you must select a prior numbered generation.
- ✓
Execute 'rollback 2' followed by 'commit'.
Why this is correct
rollback 2 sets the candidate configuration to the snapshot saved two commit operations ago, stored as /config/juniper.conf.2.gz. This bypasses the two most recent commits, returning to the last known working configuration. A subsequent commit activates this as the new active configuration, effectively undoing the problematic changes.
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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.