- A
show log messages | match ospf
Why wrong: This displays log entries, not live packet capture.
- B
show route forwarding-table
Why wrong: This shows the forwarding entries, not packet captures.
- C
show ospf neighbor detail
Why wrong: This shows OSPF neighbor status, not packet contents.
- D
monitor traffic interface ge-0/0/0.0
This command captures all packets on the interface for analysis.
Question 407 of 514
Capturing Routing Protocol Packets
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
An administrator suspects that routing protocol updates are being sent to an incorrect next-hop. Which command can be used to capture and analyze the routing protocol packets on an interface?
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.
Quick Answer
The answer is the monitor traffic interface ge-0/0/0.0 command. This command is correct because it performs a real-time packet capture directly on the specified interface, allowing you to inspect the actual contents of routing protocol packets such as OSPF or BGP updates to verify the next-hop address. On the JNCIA-Junos exam, this question tests your ability to distinguish between operational commands used for troubleshooting routing issues versus commands that display static tables or logs. A common trap is confusing monitor traffic with show route (which displays the forwarding table) or show log (which shows historical events but not live packet data). Remember that monitor traffic is Junos’s equivalent of tcpdump, giving you a live packet-level view. A helpful memory tip: “Monitor moves packets, show just shows static data”—if you need to see the actual packets flying by, think of the word “monitor” as your packet-capture trigger.
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
✓
monitor traffic interface ge-0/0/0.0
Option D is correct because the 'monitor traffic interface' command in Junos captures live packets on a specified interface, allowing the administrator to inspect routing protocol packets (e.g., OSPF, BGP) in real time. This is the only option that directly captures and displays packet-level data to verify the next-hop IP address in routing protocol updates.
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 log messages | match ospf
Why it's wrong here
This displays log entries, not live packet capture.
- ✗
show route forwarding-table
Why it's wrong here
This shows the forwarding entries, not packet captures.
- ✗
show ospf neighbor detail
Why it's wrong here
This shows OSPF neighbor status, not packet contents.
- ✓
monitor traffic interface ge-0/0/0.0
Why this is correct
This command captures all packets on the interface for analysis.
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 log-based troubleshooting (Option A) with live packet capture, or they mistakenly think that viewing the forwarding table (Option B) or neighbor details (Option C) reveals the actual packet contents being transmitted, when in fact only a packet capture tool like 'monitor traffic' can show the raw protocol updates.
Trap categories for this question
Command / output trap
This shows the forwarding entries, not packet captures.
Detailed technical explanation
How to think about this question
The 'monitor traffic interface' command uses the Junos packet capture (pcap) framework to capture packets at the interface level, including routing protocol packets like OSPF (IP protocol 89) or BGP (TCP port 179). Administrators can apply filters (e.g., 'monitor traffic interface ge-0/0/0.0 matching 'proto ospf'') to isolate specific protocol traffic, making it invaluable for troubleshooting incorrect next-hop IPs in routing updates, such as when a misconfigured OSPF interface advertises a wrong neighbor address.
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 at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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?
Routing Fundamentals — This question tests Routing Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: monitor traffic interface ge-0/0/0.0 — Option D is correct because the 'monitor traffic interface' command in Junos captures live packets on a specified interface, allowing the administrator to inspect routing protocol packets (e.g., OSPF, BGP) in real time. This is the only option that directly captures and displays packet-level data to verify the next-hop IP address in routing protocol updates.
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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Last reviewed: Jul 4, 2026
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