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.
user@router> show configuration interfaces ge-0/0/0
unit 0 {
family inet {
address 10.1.1.1/30;
}
family inet6 {
address 2001:db8::1/64;
}
}
Refer to the exhibit. What is the purpose of the 'family inet6' configuration on interface ge-0/0/0?
Refer to the exhibit.
user@router> show configuration interfaces ge-0/0/0
unit 0 {
family inet {
address 10.1.1.1/30;
}
family inet6 {
address 2001:db8::1/64;
}
}
A
To enable both IPv4 and IPv6 on the interface.
Why wrong: IPv4 is configured under 'family inet', not inet6.
B
To assign a global unicast IPv6 address to the interface.
The address 2001:db8::1/64 is a global unicast address configured under family inet6.
C
To enable IPv6 ARP on the interface.
Why wrong: IPv6 uses Neighbor Discovery Protocol (NDP), not ARP.
D
To assign a link-local IPv6 address to the interface.
Why wrong: The address 2001:db8::1/64 is a global unicast, not link-local.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To assign a global unicast IPv6 address to the interface.
The 'family inet6' configuration on interface ge-0/0/0 enables IPv6 processing on that interface. Within the 'family inet6' hierarchy, you can assign a global unicast IPv6 address using the 'address' statement. Without 'family inet6', the interface cannot process IPv6 traffic or hold an IPv6 address, making option B correct.
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.
✗
To enable both IPv4 and IPv6 on the interface.
Why it's wrong here
IPv4 is configured under 'family inet', not inet6.
✓
To assign a global unicast IPv6 address to the interface.
Why this is correct
The address 2001:db8::1/64 is a global unicast address configured under family inet6.
Related concept
Read the scenario before looking for a memorised answer.
✗
To enable IPv6 ARP on the interface.
Why it's wrong here
IPv6 uses Neighbor Discovery Protocol (NDP), not ARP.
✗
To assign a link-local IPv6 address to the interface.
Why it's wrong here
The address 2001:db8::1/64 is a global unicast, not link-local.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume 'family inet6' is needed to enable both IPv4 and IPv6, or that it is required for link-local addressing, when in fact link-local addresses are auto-generated and 'family inet6' alone does not enable IPv4.
Detailed technical explanation
How to think about this question
Under the hood, 'family inet6' activates the IPv6 protocol stack on the interface, enabling Neighbor Discovery Protocol (NDP) as per RFC 4861. A link-local IPv6 address (fe80::/10) is automatically derived from the interface's MAC address using EUI-64 or a privacy extension, so you never need to configure it manually. In real-world deployments, you must explicitly configure a global unicast address under 'family inet6' for the interface to route IPv6 traffic beyond the local link.
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: To assign a global unicast IPv6 address to the interface. — The 'family inet6' configuration on interface ge-0/0/0 enables IPv6 processing on that interface. Within the 'family inet6' hierarchy, you can assign a global unicast IPv6 address using the 'address' statement. Without 'family inet6', the interface cannot process IPv6 traffic or hold an IPv6 address, making option B correct.
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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