The answer is the 'show firewall filter log' command, because it directly displays the log entries generated by firewall filter terms that have a 'log' action configured, allowing you to see exactly which packets matched the filter and whether they were dropped. When a Junos device has a valid route in the routing table but still fails to forward traffic, a firewall filter is often silently dropping the packets without any obvious error; this command reveals those drops by showing the logged packet details, including the action taken. On the JNCIA-Junos exam, this question tests your ability to troubleshoot forwarding issues by distinguishing between routing problems and firewall filter drops—a common trap is to jump to 'show route' or 'ping' when the route is already present, but the real culprit is a filter term with a 'discard' or 'reject' action. Remember the memory tip: "If the route is there but traffic is bare, check the filter log to see what’s in the air."
JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os fundamentals. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 notices that a Junos device is not forwarding traffic for a specific subnet. The routing table shows the route for that subnet, but traffic is still not being forwarded. Which command should the engineer use to verify whether the firewall filter is dropping the traffic?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
show firewall filter log
Option D is correct because the 'show firewall filter log' command displays the log entries generated by firewall filter terms that have a 'log' action configured. When traffic is not being forwarded despite a valid route, a firewall filter may be silently dropping packets; this command reveals which packets matched the filter and whether they were logged, helping to identify drops.
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.
✗
show interfaces terse
Why it's wrong here
This shows interface status, not firewall filter drop information.
✗
show firewall filter counter
Why it's wrong here
This displays counter values but not log entries for dropped packets.
✗
show firewall filter
Why it's wrong here
This command shows the filter configuration, not dropped packet details.
✓
show firewall filter log
Why this is correct
This command displays logs of packets that match filter terms with log/syslog actions, helping identify drops.
Clue confirmation
The clue word "which command" in the question point toward this answer.
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 that candidates often confuse 'show firewall filter' (which shows configuration) with 'show firewall filter log' (which shows actual packet logs), or they assume counters alone can identify drops without realizing counters only show matches, not the specific action taken.
Trap categories for this question
Command / output trap
This shows interface status, not firewall filter drop information.
Detailed technical explanation
How to think about this question
Junos firewall filters support a 'log' action that generates a system log message for each matching packet, which can be viewed with 'show firewall filter log'. This command shows the timestamp, interface, source/destination IP, and action taken (e.g., discard). In contrast, 'show firewall filter counter' only increments a counter without logging, so it cannot provide per-packet details needed to diagnose drops. Real-world scenarios include troubleshooting black-hole routes where a filter silently discards traffic for a specific 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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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: show firewall filter log — Option D is correct because the 'show firewall filter log' command displays the log entries generated by firewall filter terms that have a 'log' action configured. When traffic is not being forwarded despite a valid route, a firewall filter may be silently dropping packets; this command reveals which packets matched the filter and whether they were logged, helping to identify drops.
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: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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