JNCIA-JUNOS Junos Configuration Basics Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos configuration basics. 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.
Exhibit
Refer to the exhibit.
[edit]
user@router# commit check
[edit interfaces xe-0/0/0 unit 0 family inet]
'address 10.1.1.1/24'
Error: Cannot configure an address on an interface that is not enabled with 'unit 0'
error: configuration check-out failed
Refer to the exhibit. What is the most likely cause of the commit check failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Refer to the exhibit.
[edit]
user@router# commit check
[edit interfaces xe-0/0/0 unit 0 family inet]
'address 10.1.1.1/24'
Error: Cannot configure an address on an interface that is not enabled with 'unit 0'
error: configuration check-out failed
A
The routing instance has not been created.
Why wrong: Not indicated by the error.
B
The interface xe-0/0/0 has been disabled using the 'disable' statement.
Disabling the interface prevents configuration of addresses on its units.
C
The IP address is a duplicate on the subnet.
Why wrong: Duplicate address error messages are different.
D
The 'family inet' statement is missing under unit 0.
Why wrong: It is present in the exhibit; the error says 'cannot configure an address on an interface that is not enabled'.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interface xe-0/0/0 has been disabled using the 'disable' statement.
The commit check failure occurs because the interface xe-0/0/0 is configured with the 'disable' statement, which prevents the interface from being enabled. When a routing instance references a disabled interface, the commit check fails because the interface cannot be used for forwarding or routing operations. Junos requires that interfaces referenced in routing instances be operationally capable of being enabled.
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 routing instance has not been created.
Why it's wrong here
Not indicated by the error.
✓
The interface xe-0/0/0 has been disabled using the 'disable' statement.
Why this is correct
Disabling the interface prevents configuration of addresses on its units.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The IP address is a duplicate on the subnet.
Why it's wrong here
Duplicate address error messages are different.
✗
The 'family inet' statement is missing under unit 0.
Why it's wrong here
It is present in the exhibit; the error says 'cannot configure an address on an interface that is not enabled'.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overlook the 'disable' statement as a valid administrative state and instead assume the failure is due to missing protocol family configuration or duplicate IP addressing, which are common but incorrect assumptions in this context.
Detailed technical explanation
How to think about this question
The 'disable' statement under an interface configuration in Junos effectively places the interface in an administratively down state, similar to 'shutdown' on Cisco IOS. When a routing instance (such as a virtual router or VRF) references a disabled interface, the commit check validates that the interface is administratively enabled; otherwise, it rejects the configuration to prevent a non-functional routing instance. This behavior is enforced by the Junos configuration parser to ensure operational consistency, as a disabled interface cannot participate in routing or forwarding.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 interface xe-0/0/0 has been disabled using the 'disable' statement. — The commit check failure occurs because the interface xe-0/0/0 is configured with the 'disable' statement, which prevents the interface from being enabled. When a routing instance references a disabled interface, the commit check fails because the interface cannot be used for forwarding or routing operations. Junos requires that interfaces referenced in routing instances be operationally capable of being enabled.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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