JN0-106 Junos OS Fundamentals Practice Question
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?
⚠ Common exam trap
Many 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.
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
✓
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.
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 (Routing Protocol Daemon) is the sole software process managing all dynamic routing protocols, including OSPF, BGP, and IS-IS. When it is killed, every established adjacency immediately tears down, causing neighboring routers to mark the node unreachable and recalculate paths. This produces route flap and forwarding loops until rpd restarts and rebuilds sessions, so the primary impact is severe routing instability.
- ✗
The CPU will be overloaded due to the kernel messages.
Why it's wrong here
The kernel messages generated when rpd is killed are a symptom of the process crash, not a cause of CPU overload. Logging a fatal error and generating a core dump consume negligible CPU cycles compared to normal router operations. Actual CPU overload would occur only from repeated crash/restart loops or massive route recalculation, but the message output itself has no significant resource impact. Thus, kernel messages do not overload the CPU.
- ✗
The router will stop forwarding packets immediately.
Why it's wrong here
Packet forwarding on Junos is performed by the Packet Forwarding Engine (PFE) using dedicated hardware ASICs, independently of the Routing Engine's rpd process. When rpd is killed, the existing forwarding table in the PFE remains intact, so traffic already being forwarded continues without interruption. Only after dynamic adjacencies are lost and routes are withdrawn will the forwarding entries for those routes be removed; static and directly connected routes stay valid. Therefore, the router will not stop forwarding packets immediately.
- ✗
The router will reboot automatically.
Why it's wrong here
Junos does not reboot the router when a user-space software process like rpd fails. The process monitoring framework automatically attempts to restart the failed daemon while the Routing Engine, chassis, and all other services continue to operate normally. A full system reboot is reserved for severe circumstances such as a kernel panic or hardware failure, not for a daemon termination. Hence, the router will not reboot automatically as a result of rpd being killed.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JN0-106 exam.