Question 88 of 514

Junos Configuration Basics →mediumMultiple ChoiceObjective-mapped

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 is configuring a new Juniper device. They intend to apply a firewall filter to an interface to only allow SSH traffic from a specific management subnet. Which configuration approach best follows Juniper best practices?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1mediummultiple choice

Review the full subnetting walkthrough →

A
Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet filter input filter-name'
This follows Juniper best practices for applying firewall filters.
B
Define the filter under 'firewall family inet' and apply it under 'interfaces lo0 unit 0 family inet filter input filter-name'
Why wrong: Applying the filter to loopback would not filter traffic on ge-0/0/0.
C
Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet input'
Why wrong: Missing 'filter' keyword; correct syntax is 'filter input filter-name'.
D
Define the filter under 'firewall family any' and apply it under 'interfaces ge-0/0/0 unit 0 family any filter input'
Why wrong: 'family any' is not specific and may not behave as expected for IPv4 traffic.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet filter input filter-name'

Option A is correct because it follows Juniper best practices by defining the firewall filter under the `firewall family inet` hierarchy (which is the standard location for IPv4 filters) and applying it as an input filter on the physical interface `ge-0/0/0 unit 0 family inet`. This configuration ensures that only SSH traffic from the specified management subnet is permitted inbound on that interface, while all other traffic is dropped by default (since firewall filters in Junos have an implicit deny at the end).

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.

✓
Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet filter input filter-name'
Why this is correct
This follows Juniper best practices for applying firewall filters.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Define the filter under 'firewall family inet' and apply it under 'interfaces lo0 unit 0 family inet filter input filter-name'
Why it's wrong here
Applying the filter to loopback would not filter traffic on ge-0/0/0.
✗
Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet input'
Why it's wrong here
Missing 'filter' keyword; correct syntax is 'filter input filter-name'.
✗
Define the filter under 'firewall family any' and apply it under 'interfaces ge-0/0/0 unit 0 family any filter input'
Why it's wrong here
'family any' is not specific and may not behave as expected for IPv4 traffic.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse the loopback interface (`lo0`) with a physical interface for applying filters, or they misremember the Junos CLI syntax by omitting the `filter` keyword or using an invalid family like `any`.

Trap categories for this question

Keyword trap
Missing 'filter' keyword; correct syntax is 'filter input filter-name'.

Detailed technical explanation

How to think about this question

Junos firewall filters are stateless and operate at Layer 3/4, using a first-match paradigm with an implicit deny-all at the end. When applied as an input filter on an interface, they inspect all incoming packets before any routing decision is made; this is distinct from output filters which inspect packets after routing. A common real-world scenario is restricting management access to a specific subnet (e.g., 10.0.1.0/24) by matching source IP and destination port 22 (SSH) in a term, then applying the filter to the interface facing that subnet.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

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.

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FAQ

Questions learners often ask

What does this JNCIA-JUNOS question test?

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: Define the filter under 'firewall family inet' and apply it under 'interfaces ge-0/0/0 unit 0 family inet filter input filter-name' — Option A is correct because it follows Juniper best practices by defining the firewall filter under the `firewall family inet` hierarchy (which is the standard location for IPv4 filters) and applying it as an input filter on the physical interface `ge-0/0/0 unit 0 family inet`. This configuration ensures that only SSH traffic from the specified management subnet is permitted inbound on that interface, while all other traffic is dropped by default (since firewall filters in Junos have an implicit deny at the end).

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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JNCIA-JUNOS exam.