Junos OS Upgrade with Graceful Switchover (GRES)
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?
Quick Answer
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.
⚠ Common exam trap
Many 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.
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
✓
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
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.
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.
- ✗
On both REs: request system software add jinstall-20.2R2.tgz reboot
Why it's wrong here
Both reboot simultaneously, causing traffic loss.
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Same concept, more angles
1 more way this is tested on JN0-106
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: 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.
JA
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.