JN0-106 Junos OS Fundamentals Practice Question
A network engineer needs to upgrade Junos on an MX router with dual Routing Engines (RE0 and RE1). What is the recommended procedure to minimize downtime?
⚠ Common exam trap
A common mix-up: candidates assume upgrading the primary first is safer or more logical, but Junos requires upgrading the backup first and performing a graceful switchover to maintain control plane continuity and avoid traffic loss.
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
✓
Upgrade the backup RE, perform a graceful switchover (RESTART ROUTING), then upgrade the former primary
It minimizes downtime by first upgrading the backup RE (RE1), then performing a graceful Routing Engine switchover (using the 'request chassis routing-engine master switch' command or equivalent), which causes the upgraded backup to become the new primary without disrupting traffic. After the switchover, the former primary (now the backup) can be upgraded and rebooted, ensuring that at least one RE is always processing traffic and routing protocols like BGP and OSPF maintain their adjacencies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upgrade the primary RE first, then the backup
Why it's wrong here
Upgrading primary first causes traffic interruption during reboot, then backup upgrade is redundant.
- ✗
Reboot both REs at the same time after copying the image
Why it's wrong here
Rebooting both simultaneously causes complete outage; no redundancy.
- ✓
Upgrade the backup RE, perform a graceful switchover (RESTART ROUTING), then upgrade the former primary
Why this is correct
This is the standard upgrade procedure for dual RE systems, minimizing traffic impact.
- ✗
Upgrade both REs simultaneously using the same image
Why it's wrong here
Simultaneous upgrade can cause both REs to reboot at the same time, leading to total loss of control plane.
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.