During a scheduled maintenance window involving the replacement of RE0 on a PTX10008 (any EVO device supporting dual-RE) RE1 (master) running Junos EVO 21.4R3-S5.9, post-replacement observations indicated a reachability issue between RE0 and RE1. Although RE1 remained the master and detected RE0 as present, communication between the Routing Engines was indicated as disrupted. This article outlines the observed symptoms, root cause, and the resolution steps taken to restore redundancy and synchronisation.

In the maintenance window of replacing the RE0 (backup), but facing an issue with the RE0 reachability with RE1 (master) after replacing it with the new HW.

RE1 running master, and RE0 was showing as present on RE1 (master) in "show chassis routing-engine" output. 

• RE0 was replaced with an RMA unit during maintenance window.
• RE1 (master) detected RE0 as present, was indicating that RE0 was not reachable for RE1 (master).
• On Console display of identified that RE0 failed to boot properly even after attempting to reboot with help of site engineer by re-seat.
• Console access to RE0 showed failed recovery attempts and unsuccessful reboots from alternate GRUB partitions also.
• Attempted to reboot with alternative partition from vmhost alternate media on RE0 console however no luck. 
• This was indicating as RE0 delivered from RMA is observing software error or not installed properly or if possible disk errors.

user@router1-re1> show version 
Hostname: router1-re1
Model: ptx10008
Junos: 21.4R3-S5.9-EVO
Yocto: 2.2.1
Linux Kernel: 4.8.28-WR2.2.1_standard-gea7287e
JUNOS-EVO OS 64-bit [junos-evo-install-ptx-x86-64-21.4R3-S5.9-EVO]

The newly installed RE0 had a mismatched or corrupted software image and configuration, preventing it from synchronising with the master RE1. This led to a partial communication failure between the Routing Engines.

Please check for alarm log for verison mismatch using command "show chassis alarm".

From the master RE (RE1), execute the following command to synchronise software and configuration:

request system software sync all-versions

• This command ensures that the software image, scripts and configuration from the master RE are replicated to the backup RE.
• It also triggers a reboot of the backup RE (RE0) to apply the synchronised image.
• Post-synchronisation, RE0 booted up with the same Junos version and configuration as RE1.
• Health checks passed, and mastership was successfully transferred to RE0.
• Nonstop Routing (NSR) and Graceful Routing Engine Switchover (GRES) ensured no traffic impact during the transition.
• Post-replacement verification confirmed stable operation and restored redundancy.

For more details, please refer below link :

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/request-system-software-sync.html

CLI COMMAND : request system software sync (current | rollback | all-versions)

Use this command on the primary Routing Engine of a system to synchronize the software and configurations from the primary Routing Engine to the other nodes and reboot the other nodes. The configurations are synchronized even if the images are not identical. If specified on the backup Routing Engine, the command fails. This command does not impact traffic forwarding.

2025-10-21 : Article Created

2026-03-06 : Adding platform QFX.