The correct answer is that routing protocol adjacencies will be lost, causing routing instability. This occurs because a Packet Forwarding Engine (PFE) reset, often triggered by a hardware fault like an FPC crash or PIC restart, severs the communication link between the control plane and the forwarding plane. In Junos, the control plane relies on the PFE to maintain active adjacency states for protocols such as OSPF, BGP, and IS-IS; when the PFE resets, all these adjacencies are immediately torn down, leading to route withdrawal and instability until the adjacencies re-establish. On the JNCIA-Junos exam, this concept tests your understanding of the separation between the control and forwarding planes and how critical events like a Junos PFE reset directly impact routing protocol adjacency loss. A common trap is assuming only the forwarding plane is affected, but remember: the control plane cannot maintain adjacencies without a functioning PFE. Memory tip: "PFE down, neighbors gone" — any PFE reset means all routing adjacencies drop.
JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os 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.
Exhibit
Refer to the exhibit.
user@router> show log messages | match "kernel"
Jan 10 10:00:00 router kernel: pid 1234 (rpd), uid 0, was killed: out of swap space
Jan 10 10:00:01 router kernel: pid 1235 (rpd), uid 0, was killed: out of swap space
Based on the exhibit, what is the most likely impact on the router?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Refer to the exhibit.
user@router> show log messages | match "kernel"
Jan 10 10:00:00 router kernel: pid 1234 (rpd), uid 0, was killed: out of swap space
Jan 10 10:00:01 router kernel: pid 1235 (rpd), uid 0, was killed: out of swap space
A
Routing protocol adjacencies will be lost, causing routing instability.
The rpd process is killed, so dynamic routing protocols will fail.
B
The CPU will be overloaded due to the kernel messages.
Why wrong: The messages are a symptom, not a cause of CPU overload.
C
The router will stop forwarding packets immediately.
Why wrong: Static routes and hardware forwarding may continue until the next reboot or configuration change.
D
The router will reboot automatically.
Why wrong: No automatic reboot is triggered by process kill.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Routing protocol adjacencies will be lost, causing routing instability.
The exhibit shows kernel messages indicating a hardware or software fault (e.g., a FPC crash or PIC restart). In Junos, such critical events cause the Packet Forwarding Engine (PFE) to reset, which tears down all routing protocol adjacencies (OSPF, BGP, IS-IS) because the control plane loses communication with the forwarding plane. This leads to route withdrawal and routing instability until the adjacencies are re-established.
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.
✓
Routing protocol adjacencies will be lost, causing routing instability.
Why this is correct
The rpd process is killed, so dynamic routing protocols will fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The CPU will be overloaded due to the kernel messages.
Why it's wrong here
The messages are a symptom, not a cause of CPU overload.
✗
The router will stop forwarding packets immediately.
Why it's wrong here
Static routes and hardware forwarding may continue until the next reboot or configuration change.
✗
The router will reboot automatically.
Why it's wrong here
No automatic reboot is triggered by process kill.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume kernel messages always cause a full reboot or immediate forwarding stop, but Junos is designed to isolate failures to specific components (like FPCs) rather than crashing the entire router.
Detailed technical explanation
How to think about this question
Under the hood, Junos separates the control plane (Routing Engine) from the forwarding plane (PFE). When a kernel panic or hardware fault occurs in the PFE, the RE logs the event and triggers a graceful restart or FPC restart. During this process, routing protocol adjacencies are torn down because the RE cannot exchange keepalives or update the forwarding table, but the router may use graceful restart mechanisms (e.g., OSPF graceful restart, BGP graceful restart) to minimize impact if configured. In real-world scenarios, this is common during line card failures in MX or PTX series routers.
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.
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: Routing protocol adjacencies will be lost, causing routing instability. — The exhibit shows kernel messages indicating a hardware or software fault (e.g., a FPC crash or PIC restart). In Junos, such critical events cause the Packet Forwarding Engine (PFE) to reset, which tears down all routing protocol adjacencies (OSPF, BGP, IS-IS) because the control plane loses communication with the forwarding plane. This leads to route withdrawal and routing instability until the adjacencies are re-established.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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