JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os 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.
Exhibit
Refer to the exhibit.
user@router> show log messages | match "sshd"
Mar 20 10:20:00 router sshd[1234]: Failed password for root from 192.168.1.100 port 22 ssh2
Mar 20 10:20:10 router sshd[1235]: Failed password for root from 192.168.1.100 port 22 ssh2
Mar 20 10:20:20 router sshd[1236]: Failed password for root from 192.168.1.100 port 22 ssh2
Refer to the exhibit. An administrator notices repeated failed login attempts. What should be configured to mitigate this attack?
Refer to the exhibit.
user@router> show log messages | match "sshd"
Mar 20 10:20:00 router sshd[1234]: Failed password for root from 192.168.1.100 port 22 ssh2
Mar 20 10:20:10 router sshd[1235]: Failed password for root from 192.168.1.100 port 22 ssh2
Mar 20 10:20:20 router sshd[1236]: Failed password for root from 192.168.1.100 port 22 ssh2
A
Set login retry limit
Why wrong: A would not block the ongoing attack immediately.
B
Configure a firewall filter to block the source IP
B directly blocks the attacker IP.
C
Disable SSH
Why wrong: C disrupts legitimate access.
D
Change the root password
Why wrong: D does not prevent brute force from other IPs.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a firewall filter to block the source IP
A firewall filter can block traffic from the source IP address of the repeated failed login attempts, preventing further access from that host. This is a direct and immediate mitigation against an ongoing brute-force attack, as it stops the attacker's traffic at the network layer before it reaches the SSH or login service.
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 login retry limit
Why it's wrong here
A would not block the ongoing attack immediately.
✓
Configure a firewall filter to block the source IP
Why this is correct
B directly blocks the attacker IP.
Related concept
Read the scenario before looking for a memorised answer.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse mitigation (stopping an ongoing attack) with prevention (hardening against future attacks), leading them to choose retry limits or password changes instead of the immediate IP-blocking solution.
Detailed technical explanation
How to think about this question
Junos firewall filters operate at the packet forwarding level, using stateless or stateful inspection to match on source IP, destination port, and other criteria. In a real-world scenario, an administrator would first identify the offending source IP from the system logs (e.g., /var/log/messages or using 'show log interactive-commands'), then apply a firewall filter term that rejects or discards packets from that IP to the management interface (e.g., fxp0 or em0). This approach is more efficient than rate-limiting or retry limits because it stops the attack traffic entirely at the network edge.
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 OS Fundamentals — This question tests Junos OS Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a firewall filter to block the source IP — A firewall filter can block traffic from the source IP address of the repeated failed login attempts, preventing further access from that host. This is a direct and immediate mitigation against an ongoing brute-force attack, as it stops the attacker's traffic at the network layer before it reaches the SSH or login service.
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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