The correct method is to use the `set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 secondary` command. This is required because Junos treats the first IP address assigned to a logical interface unit as the primary address, and any additional IPv4 addresses must be explicitly marked with the `secondary` keyword to coexist on the same unit. On the JNCIA-Junos exam, this concept tests your understanding of interface address hierarchy and the Junos configuration syntax for multi-address support. A common trap is forgetting the `secondary` keyword, which would cause the new address to replace the existing primary address instead of being added alongside it. Remember the memory tip: "First is primary, rest need the secondary test."
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.
A network engineer needs to add an additional IP address to an interface that already has a primary IP configured. Which method should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 secondary
Option B is correct because in Junos, to add an additional IP address to an interface that already has a primary IP configured, you must append the 'secondary' keyword to the address configuration statement. This allows multiple IPv4 addresses on the same logical interface unit, with the first address assigned being the primary and subsequent addresses marked as secondary.
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.
✗
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24
Why it's wrong here
Would replace the existing address if not specified as secondary.
✓
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 secondary
Why this is correct
Correct syntax for adding a secondary address.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
set interfaces ge-0/0/0 unit 0 family inet secondary address 10.0.0.2/24
Why it's wrong here
Wrong hierarchy; 'secondary' is a parameter of address.
✗
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 primary
Why it's wrong here
Would replace the existing primary.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates familiar with Cisco IOS might use the 'secondary' keyword as a subcommand under the interface (e.g., 'ip address 10.0.0.2 255.255.255.0 secondary'), but in Junos, the correct syntax places 'secondary' after the address in the same configuration line, not as a separate hierarchy.
Detailed technical explanation
How to think about this question
In Junos, each logical interface unit can have multiple IPv4 addresses, but only one is designated as the primary (used for source address selection by default). The 'secondary' keyword ensures the address is added without altering the existing primary. This is critical in scenarios like BGP multihop or management access where multiple subnets must be reachable on the same interface, and the primary address is used for routing protocol updates unless overridden.
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: set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 secondary — Option B is correct because in Junos, to add an additional IP address to an interface that already has a primary IP configured, you must append the 'secondary' keyword to the address configuration statement. This allows multiple IPv4 addresses on the same logical interface unit, with the first address assigned being the primary and subsequent addresses marked as secondary.
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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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