- A
Use 'load override /config/juniper.conf.1.gz' followed by 'commit'.
Why wrong: While the file /config/juniper.conf.1.gz might contain the previous configuration, the standard Junos method is to use 'rollback' commands. Loading override manually could work but is not the recommended or reliable approach in this context.
- B
Use 'delete system' to remove all configuration and then commit.
Why wrong: Deleting all system configuration would remove essential settings and likely break connectivity further, not restore the previous config.
- C
Execute 'rollback 0' followed by 'commit'.
Why wrong: Rollback 0 refers to the current active configuration, which is the problematic one. This would not change anything.
- D
Execute 'rollback 1' followed by 'commit'.
Rollback 1 reverts to the configuration that was committed before the current one, which is the working configuration. Commit activates it.
Quick Answer
The answer is to execute 'rollback 1' followed by 'commit'. This is correct because the rollback command in Junos references the number of commits to go back from the current active configuration, not the total number of changes made. Since the engineer needs to revert two commits from the current state, and the current active configuration is the problematic one, 'rollback 1' retrieves the configuration that was active one commit prior—which is the working configuration. After the rollback, a commit makes that candidate configuration active, restoring connectivity. On the JNCIA-Junos exam, this tests your understanding of the Junos commit model and the rollback command's indexing, where rollback 0 is the current active configuration, rollback 1 is the previous commit, and so on. A common trap is confusing the rollback number with the number of changes made; remember that rollback counts commits, not individual edits. Memory tip: think of rollback as a time machine that goes back one commit at a time—rollback 1 takes you to the last working state.
JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os fundamentals. 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 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?
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 1' followed by 'commit'.
Option D is correct because the 'rollback 1' command reverts the candidate configuration to the configuration that was active one commit prior to the current active configuration. Since the engineer needs to go back two commits from the current state, and the current active configuration is the problematic one, 'rollback 1' retrieves the configuration from the previous commit (the working one). After the rollback, a 'commit' makes that configuration active, restoring connectivity.
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.
- ✗
Use 'load override /config/juniper.conf.1.gz' followed by 'commit'.
Why it's wrong here
While the file /config/juniper.conf.1.gz might contain the previous configuration, the standard Junos method is to use 'rollback' commands. Loading override manually could work but is not the recommended or reliable approach in this context.
- ✗
Use 'delete system' to remove all configuration and then commit.
Why it's wrong here
Deleting all system configuration would remove essential settings and likely break connectivity further, not restore the previous config.
- ✗
Execute 'rollback 0' followed by 'commit'.
Why it's wrong here
Rollback 0 refers to the current active configuration, which is the problematic one. This would not change anything.
- ✓
Execute 'rollback 1' followed by 'commit'.
Why this is correct
Rollback 1 reverts to the configuration that was committed before the current one, which is the working configuration. Commit activates it.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing 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).
Trap categories for this question
Command / output trap
While the file /config/juniper.conf.1.gz might contain the previous configuration, the standard Junos method is to use 'rollback' commands. Loading override manually could work but is not the recommended or reliable approach in this context.
Detailed technical explanation
How to think about this question
Junos maintains a commit history of up to 50 previous configurations, accessible via 'rollback N' where N=0 is the current active configuration, N=1 is the previous commit, N=2 is two commits ago, etc. The rollback command copies the specified historical configuration into the candidate configuration, allowing review and modification before commit. This is distinct from the 'load override' command, which loads a configuration file from the filesystem (e.g., from /config/) into the candidate configuration, and is typically used for restoring from external backups or automated provisioning.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Junos OS Fundamentals — This question tests Junos OS Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Execute 'rollback 1' followed by 'commit'. — Option D is correct because the 'rollback 1' command reverts the candidate configuration to the configuration that was active one commit prior to the current active configuration. Since the engineer needs to go back two commits from the current state, and the current active configuration is the problematic one, 'rollback 1' retrieves the configuration from the previous commit (the working one). After the rollback, a 'commit' makes that configuration active, restoring connectivity.
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.
What is the key concept behind this question?
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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