The answer is that the candidate configuration is replaced with the configuration from three commits ago. This is correct because Junos maintains a rollback history of up to 50 slots, numbered 0 through 49, where slot 0 always holds the most recently committed configuration. When you issue the rollback 3 command, you are instructing the system to overwrite your current candidate configuration with the exact state saved in slot 3, which is the configuration from three commits prior. On the JNCIA-Junos exam, this concept tests your understanding of Junos configuration management and the rollback slot numbering scheme, which is a common trap: many candidates mistakenly think rollback 3 reverts to the third commit from the beginning, rather than counting backward from the most recent. A reliable memory tip is to remember that rollback slots work like a countdown from zero—slot 0 is now, slot 1 is one step back, so rollback N always means go back N commits from the present.
JNCIA-JUNOS Junos Configuration Basics Practice Question
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.
An engineer issues the 'rollback 3' command in configuration mode. What is the effect?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The candidate configuration is replaced with the configuration from three commits ago.
The 'rollback 3' command in Junos configuration mode replaces the current candidate configuration with the configuration from the third most recent commit. Junos maintains up to 50 rollback slots (numbered 0 through 49), where slot 0 is the most recent commit, slot 1 is the commit before that, and so on. Therefore, 'rollback 3' retrieves the configuration saved three commits ago, overwriting any uncommitted changes in the candidate configuration.
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.
✗
The candidate configuration is saved as the third rollback slot.
Why it's wrong here
Rollback loads a saved configuration, not save.
✓
The candidate configuration is replaced with the configuration from three commits ago.
Why this is correct
Rollback loads a previous configuration into the candidate.
Related concept
Read the scenario before looking for a memorised answer.
✗
The active configuration is replaced with the candidate configuration.
Why it's wrong here
Rollback does not affect the active configuration until commit.
✗
The device reboots and loads configuration version 3.
Why it's wrong here
No reboot occurs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'rollback' with 'commit' or 'save' operations, mistakenly thinking it saves the current candidate configuration rather than retrieving a previous one, or they assume it directly modifies the active configuration without requiring a subsequent commit.
Detailed technical explanation
How to think about this question
Junos stores committed configurations in a circular buffer of up to 50 rollback slots, accessible via 'rollback <n>'. The 'rollback 0' command loads the most recent commit, while 'rollback 1' loads the one before that, and so on. This mechanism is part of Junos's configuration management system, which allows rapid recovery from misconfigurations without requiring external backups. In real-world scenarios, an engineer might use 'rollback 3' to revert to a known-good configuration after a series of faulty commits, then commit the candidate to restore service.
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.
Junos Configuration Basics — This question tests Junos Configuration Basics — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The candidate configuration is replaced with the configuration from three commits ago. — The 'rollback 3' command in Junos configuration mode replaces the current candidate configuration with the configuration from the third most recent commit. Junos maintains up to 50 rollback slots (numbered 0 through 49), where slot 0 is the most recent commit, slot 1 is the commit before that, and so on. Therefore, 'rollback 3' retrieves the configuration saved three commits ago, overwriting any uncommitted changes in the candidate configuration.
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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Question Discussion
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