- A
Use 'request system software add <image> re1' and then 'request system reboot re1'
This sequence adds the image to re1 only and reboots only that RE. The primary RE continues running, so forwarding is unaffected.
- B
Use 'request system software add <image> both' and then 'request system reboot both'
Why wrong: This adds the image to both REs and reboots both, causing a full system outage. It does not isolate the upgrade to the backup.
- C
Use 'request system software add <image> re0' and then 'request system reboot re0'
Why wrong: This affects re0, which is typically the primary RE. Rebooting the primary RE would disrupt forwarding.
- D
Copy the image to both REs and reboot the backup RE with 'request system reboot slice 1'
Why wrong: Copying the image to both REs may affect the primary RE. Also, 'request system reboot slice 1' is not a valid command for RE reboot.
Quick Answer
The answer is to use 'request system software add <image> re1' followed by 'request system reboot re1'. This is correct because the first command targets the installation exclusively to the backup Routing Engine (RE1), and the second command reboots only that RE, leaving the primary RE (RE0) untouched and the forwarding plane fully operational. On the JNCIA-Junos exam, this scenario tests your understanding of dual-RE architecture and the precise syntax required to upgrade only the backup routing engine without impacting traffic. A common trap is assuming a system-wide reboot or using the 'request system software add' command without specifying the RE, which would disrupt the active forwarding plane. Remember the key distinction: you must explicitly target the backup RE in both the install and reboot commands to isolate the upgrade. A helpful memory tip is "Backup first, target the one"—always append 're1' to both commands when you need to upgrade the backup routing engine only.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. 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.
A network operator needs to upgrade the Junos OS on the backup RE (re1) of a dual-RE system. Which procedure ensures that only the backup RE is upgraded and rebooted without affecting the forwarding plane?
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
Use 'request system software add <image> re1' and then 'request system reboot re1'
Option A is correct because the 'request system software add <image> re1' command installs the Junos OS image only on the backup Routing Engine (RE1), and the subsequent 'request system reboot re1' reboots only that RE. In a dual-RE system, this procedure isolates the upgrade to the backup RE, ensuring the forwarding plane remains active on the primary RE (RE0) and no traffic disruption occurs.
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.
- ✓
Use 'request system software add <image> re1' and then 'request system reboot re1'
Why this is correct
This sequence adds the image to re1 only and reboots only that RE. The primary RE continues running, so forwarding is unaffected.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use 'request system software add <image> both' and then 'request system reboot both'
Why it's wrong here
This adds the image to both REs and reboots both, causing a full system outage. It does not isolate the upgrade to the backup.
- ✗
Use 'request system software add <image> re0' and then 'request system reboot re0'
Why it's wrong here
This affects re0, which is typically the primary RE. Rebooting the primary RE would disrupt forwarding.
- ✗
Copy the image to both REs and reboot the backup RE with 'request system reboot slice 1'
Why it's wrong here
Copying the image to both REs may affect the primary RE. Also, 'request system reboot slice 1' is not a valid command for RE reboot.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse the 'both' option with a safe upgrade method, not realizing it reboots both REs simultaneously and disrupts traffic, or they may incorrectly assume that copying the image manually and using a non-existent 'slice' command is a valid procedure.
Trap categories for this question
Command / output trap
Copying the image to both REs may affect the primary RE. Also, 'request system reboot slice 1' is not a valid command for RE reboot.
Detailed technical explanation
How to think about this question
In a dual-RE Junos system, the Routing Engines operate in a master/backup configuration with a graceful Routing Engine switchover (GRES) capability. The 'request system software add' command with the 're1' option installs the image to the backup RE's /altroot partition, and the subsequent reboot triggers a warm start that does not affect the Packet Forwarding Engine (PFE) on the master RE. This procedure is critical for non-disruptive upgrades in high-availability environments, such as core routers or MX series platforms, where maintaining forwarding continuity is essential.
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 practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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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Operational Monitoring and Maintenance — study guide chapter
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use 'request system software add <image> re1' and then 'request system reboot re1' — Option A is correct because the 'request system software add <image> re1' command installs the Junos OS image only on the backup Routing Engine (RE1), and the subsequent 'request system reboot re1' reboots only that RE. In a dual-RE system, this procedure isolates the upgrade to the backup RE, ensuring the forwarding plane remains active on the primary RE (RE0) and no traffic disruption occurs.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This JNCIA-JUNOS 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 JNCIA-JUNOS exam.
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