This JNCIA-JUNOS practice question tests your understanding of user interfaces. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
You are a network engineer responsible for a Juniper MX240 router in a data center. The router is running Junos 18.2R1 and you need to upgrade it to 19.1R2 to fix a critical security vulnerability. You establish an SSH session to the router and enter configuration mode to prepare the upgrade. While in configuration mode, you notice that the candidate configuration contains several uncommitted changes from a previous engineer that attempted to modify BGP settings but introduced a syntax error. The candidate configuration fails any commit operation due to this error. The currently active configuration is stable and the router is handling production traffic. The upgrade process requires you to change the boot media and specify the new image. Which action should you take to clear the candidate configuration and proceed with the upgrade?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands.
Option B is correct because the 'rollback 0' command discards all uncommitted changes in the candidate configuration and replaces it with the active, committed configuration. This clears the syntax error without affecting the running router, allowing you to proceed with the upgrade commands (e.g., 'request system software add') without a reboot or forced commit.
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.
✗
Reboot the router to clear the candidate configuration and then start the upgrade.
Why it's wrong here
Reboot does not clear candidate; it just restarts.
✓
Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands.
Why this is correct
This clears the problematic candidate while preserving the active config.
Related concept
Read the scenario before looking for a memorised answer.
✗
Run the 'load override terminal' command and paste the active configuration from memory, then commit and upgrade.
Why it's wrong here
This is inefficient and error-prone; rollback is simpler.
✗
Use the 'commit force' command to override the syntax error and commit the candidate, then perform the upgrade.
Why it's wrong here
There is no 'commit force' command; commit requires valid syntax.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think a reboot is needed to clear uncommitted changes (Option A) or that 'commit force' can bypass syntax errors (Option D), when in fact Junos provides a dedicated 'rollback' command to safely discard the candidate configuration without impacting the active state.
Trap categories for this question
Command / output trap
There is no 'commit force' command; commit requires valid syntax.
Detailed technical explanation
How to think about this question
In Junos, the candidate configuration is a separate copy from the active configuration; 'rollback 0' reverts the candidate to the last committed configuration (stored in /config/juniper.conf.gz). The upgrade process (e.g., 'request system software add') does not require a clean candidate, but a failed commit due to syntax errors can block subsequent commits needed for the upgrade. The 'rollback' command is non-disruptive and operates entirely in the configuration database, making it the standard method to discard uncommitted changes.
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 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
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.
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands. — Option B is correct because the 'rollback 0' command discards all uncommitted changes in the candidate configuration and replaces it with the active, committed configuration. This clears the syntax error without affecting the running router, allowing you to proceed with the upgrade commands (e.g., 'request system software add') without a reboot or forced commit.
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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