- A
First configure match conditions, then configure the action, and finally apply the filter to the interface.
This is correct because you must define what traffic to match (from clause) and what action to take (then clause) before applying the filter to an interface. Applying the filter without a complete term would result in an incomplete configuration.
- B
First apply the filter to the interface, then configure match conditions, then configure the action.
Why wrong: This is incorrect because the firewall filter does not exist yet when you apply it to the interface. The filter must be defined with terms before it can be applied.
- C
First configure the action, then configure match conditions, then apply the filter to the interface.
Why wrong: This is incorrect because the action (then clause) is meaningless without match conditions. In Junos, the term is structured as 'from' (match) then 'then' (action); setting action first does not cause a syntax error but is logically backwards.
- D
First configure match conditions, then apply the filter to the interface, then configure the action.
Why wrong: This is incorrect because applying the filter before configuring the action leaves the filter with an incomplete term. The filter must have both match conditions and an action defined to be effective.
How to Configure Firewall Filters in Junos
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. 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.
Order the steps to configure firewall filters (ACLs) in Junos.
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
First configure match conditions, then configure the action, and finally apply the filter to the interface.
Firewall filters are defined with terms (match conditions and actions) and applied to interfaces.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
First configure match conditions, then configure the action, and finally apply the filter to the interface.
Why this is correct
This is correct because you must define what traffic to match (from clause) and what action to take (then clause) before applying the filter to an interface. Applying the filter without a complete term would result in an incomplete configuration.
Related concept
Standard ACLs match source addresses.
- ✗
First apply the filter to the interface, then configure match conditions, then configure the action.
Why it's wrong here
This is incorrect because the firewall filter does not exist yet when you apply it to the interface. The filter must be defined with terms before it can be applied.
- ✗
First configure the action, then configure match conditions, then apply the filter to the interface.
Why it's wrong here
This is incorrect because the action (then clause) is meaningless without match conditions. In Junos, the term is structured as 'from' (match) then 'then' (action); setting action first does not cause a syntax error but is logically backwards.
- ✗
First configure match conditions, then apply the filter to the interface, then configure the action.
Why it's wrong here
This is incorrect because applying the filter before configuring the action leaves the filter with an incomplete term. The filter must have both match conditions and an action defined to be effective.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related JNCIA-JUNOS ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Routing Fundamentals — This question tests Routing Fundamentals — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: First configure match conditions, then configure the action, and finally apply the filter to the interface. — Firewall filters are defined with terms (match conditions and actions) and applied to interfaces.
What should I do if I get this JNCIA-JUNOS question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related JNCIA-JUNOS ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 11, 2026
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