The correct sequence is to upgrade the backup RE first, reboot it, then switch mastership to the upgraded RE, and finally upgrade the original master RE. This order is essential because it leverages Graceful Routing Engine Switchover (GRES) to maintain BGP sessions and VPN forwarding without interruption; by upgrading the standby RE while the active RE continues handling traffic, you ensure that control plane functions are preserved during the Junos OS upgrade with GRES minimal disruption. On the JNCIA-Junos exam, this scenario tests your understanding of non-disruptive upgrade procedures for dual-RE platforms, often appearing as a sequence-ordering question where the common trap is to upgrade the master RE first, which would cause a full reboot and traffic loss. Remember the mnemonic: "Backup first, then switch, then master last" — this ensures the backup becomes the new master before the old master is touched, keeping BGP and VPN forwarding alive throughout the process.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
You are managing a Juniper MX router that serves as a BGP route reflector for multiple customer VPNs. The router has two routing engines (RE0 and RE1) in a graceful switchover (GRES) configuration. During a routine maintenance window, you need to upgrade the Junos OS from version 18.1R1 to 20.2R2. The upgrade must minimize traffic disruption. You have already staged the new image on both REs. Which sequence of commands ensures minimal impact?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
On RE0: request system reboot (without adding software)
Why wrong: Reboots without upgrading.
C
On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot
Minimizes downtime by upgrading backup first, then switching.
D
On both REs: request system software add jinstall-20.2R2.tgz reboot
Why wrong: Both reboot simultaneously, causing traffic loss.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot
Option C is correct because it performs a non-disruptive upgrade by first upgrading the backup RE (RE1), then switching mastership to the upgraded RE, and finally upgrading the original master RE. This sequence leverages Graceful Routing Engine Switchover (GRES) to maintain BGP sessions and VPN forwarding during the upgrade, minimizing traffic disruption.
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.
✗
On RE0: request system software add jinstall-20.2R2.tgz reboot; then on RE1 same command
Why it's wrong here
Upgrades primary first, causing longer downtime.
✗
On RE0: request system reboot (without adding software)
Why it's wrong here
Reboots without upgrading.
✓
On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot
Why this is correct
Minimizes downtime by upgrading backup first, then switching.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
On both REs: request system software add jinstall-20.2R2.tgz reboot
Why it's wrong here
Both reboot simultaneously, causing traffic loss.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume rebooting both REs sequentially with the same command is sufficient, but they overlook the need to switch mastership to the upgraded backup RE before upgrading the original master to avoid a double-reboot scenario that disrupts traffic.
Detailed technical explanation
How to think about this question
GRES allows the backup RE to take over forwarding state seamlessly if the master RE fails or is rebooted, but it requires both REs to run the same Junos version. The upgrade sequence in option C ensures that at least one RE is always running the new software and acting as master, while the other is being upgraded, preserving BGP route reflection and VPN service continuity. The 'request chassis routing-engine master switch' command triggers a controlled mastership switch, which is cleaner than a forced reboot of the master.
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.
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: On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot — Option C is correct because it performs a non-disruptive upgrade by first upgrading the backup RE (RE1), then switching mastership to the upgraded RE, and finally upgrading the original master RE. This sequence leverages Graceful Routing Engine Switchover (GRES) to maintain BGP sessions and VPN forwarding during the upgrade, minimizing traffic disruption.
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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which three steps are part of a typical software upgrade process on a Juniper device? (Choose three.)
hard
✓ A.Issue the request system software add command
✓ B.Download the image to /var/tmp
C.Shut down all interfaces
D.Delete the old image before adding the new one
✓ E.Reboot the device
Why A: Option A is correct because the 'request system software add' command is the standard Junos CLI command used to initiate the installation of a new software image on a Juniper device. This command triggers the process of copying the image from a specified source (e.g., a URL or local file) into the system's active software partition, preparing it for the next reboot.
Last reviewed: Jun 11, 2026
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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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