The answer is that the commit command activates all candidate changes atomically, meaning both the interface address and security policy will be applied simultaneously. This is correct because Junos uses a two-phase configuration model: changes are first made to a candidate configuration, then the commit command validates and activates every change as a single, all-or-nothing transaction. If any syntax error exists, the entire commit fails and no changes take effect—errors are never ignored. On the JNCIA-Junos exam, this concept tests your understanding of Junos’s atomic commit behavior, which is a key differentiator from other vendors; a common trap is assuming changes activate incrementally or that a reboot is needed for policy updates. Remember the memory tip: “Commit is all or nothing—if one change fails, none succeed.”
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.
Exhibit
Refer to the exhibit.
[edit]
user@router# show | compare
[edit interfaces ge-0/0/0 unit 0 family inet]
+ address 10.0.0.1/24;
[edit security]
+ policies {
+ from-zone trust to-zone untrust {
+ policy permit-all {
+ match {
+ source-address any;
+ destination-address any;
+ application any;
+ }
+ then {
+ permit;
+ }
+ }
+ }
+ }
Refer to the exhibit. An engineer has made changes to the candidate configuration. What will happen when the engineer issues the 'commit' command?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Both the interface address and security policy will be activated.
Option D is correct because in Junos, the 'commit' command activates all changes in the candidate configuration atomically. Both the interface address change and the security policy will be applied simultaneously after validation. Junos does not require a reboot for security policy changes, and syntax errors cause the commit to fail, not be ignored.
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 commit will succeed but the security policy will be ignored due to a syntax error.
Why it's wrong here
No syntax error is present.
✗
Only the interface address change will be committed because security policies require a reboot.
Why it's wrong here
Security policies do not require a reboot.
✗
The configuration will be validated; if errors exist, the commit will fail.
Why it's wrong here
Validation occurs, but the exhibit shows no errors.
✓
Both the interface address and security policy will be activated.
Why this is correct
Commit activates all changes in the candidate configuration.
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 that candidates may think security policies require a reboot (a common misconception from other platforms) or that syntax errors are silently ignored, but Junos enforces strict validation and atomic commits.
Trap categories for this question
Command / output trap
Validation occurs, but the exhibit shows no errors.
Detailed technical explanation
How to think about this question
Junos uses a two-phase commit model: the candidate configuration is first validated against the schema and operational constraints (e.g., interface addresses must be in valid subnet format, security policies must reference existing zones). If validation passes, the commit applies all changes as a single transaction, ensuring consistency. This is similar to a database transaction, where either all changes take effect or none do, preventing partial configuration states.
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: Both the interface address and security policy will be activated. — Option D is correct because in Junos, the 'commit' command activates all changes in the candidate configuration atomically. Both the interface address change and the security policy will be applied simultaneously after validation. Junos does not require a reboot for security policy changes, and syntax errors cause the commit to fail, not be ignored.
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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