The correct configuration is set interfaces fxp0 unit 0 family inet filter input allow-ssh, because the management interface on Juniper devices is fxp0, and applying a firewall filter to the inet family in the input direction restricts all inbound traffic before it reaches the Routing Engine. This ensures that only SSH traffic, permitted by the allow-ssh filter on TCP port 22, can access the management interface, blocking other protocols like Telnet or HTTP. On the JNCIA-Junos exam, this question tests your understanding that fxp0 is a dedicated out-of-band management port, distinct from network-facing interfaces, and that firewall filters must be applied to the correct family (inet) and direction (input) to control management plane access. A common trap is confusing fxp0 with the loopback interface lo0, or forgetting that the filter must explicitly deny all other traffic by default. Memory tip: think “fxp0 = filter input” — the management interface always uses input filters to guard the control plane.
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 junior engineer is tasked with configuring a firewall filter to only allow SSH access to the management interface. The management interface is fxp0. Which configuration is correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
set interfaces fxp0 unit 0 family inet filter input allow-ssh
Option D is correct because the management interface on Juniper devices is fxp0, and applying a firewall filter to its inet family input direction restricts inbound traffic. The filter 'allow-ssh' must permit only TCP port 22, blocking all other management access. This configuration ensures SSH-only access to the management interface.
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 lo0 unit 0 family inet filter input allow-ssh
Why it's wrong here
Loopback is not the management interface; fxp0 is.
✗
set groups management-filter interfaces fxp0 unit 0 family inet filter input allow-ssh
Why it's wrong here
apply-groups is not used to apply filters directly.
✗
set interfaces ge-0/0/0 unit 0 family inet filter input allow-ssh
Why it's wrong here
ge-0/0/0 is not the management interface; fxp0 is.
✓
set interfaces fxp0 unit 0 family inet filter input allow-ssh
Why this is correct
Correctly applies the filter to the management interface.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing the management interface (fxp0) with the loopback interface (lo0) or a data-plane interface (ge-0/0/0), leading candidates to apply the filter to the wrong interface.
Detailed technical explanation
How to think about this question
The fxp0 interface is a dedicated out-of-band management Ethernet port on Juniper devices, separate from the data-plane interfaces. Firewall filters on fxp0 are processed by the Routing Engine's packet forwarding engine, not the data-plane ASICs, ensuring management access control even under heavy traffic load. In real-world deployments, this filter should explicitly allow SSH (TCP/22) and optionally deny all other traffic to prevent unauthorized management access.
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.
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 fxp0 unit 0 family inet filter input allow-ssh — Option D is correct because the management interface on Juniper devices is fxp0, and applying a firewall filter to its inet family input direction restricts inbound traffic. The filter 'allow-ssh' must permit only TCP port 22, blocking all other management access. This configuration ensures SSH-only access to the management interface.
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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Question Discussion
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