This article shows how to upgrade a two-member Juniper Networks QFX/EX Series Virtual Chassis when the nonstop software upgrade (NSSU) process is either not available or undesirable. This process minimizes service disruption and has minimal impact on data center workloads.

The Virtual Chassis feature employs a primary/backup system to maintain synchronized device states among the members of the Virtual Chassis. While one device manages the traffic, we temporarily take the other device offline to perform an upgrade. To upgrade both devices, we follow these steps:

1. First, we shift all traffic to the primary device.
2. Once the backup device is no longer handling server traffic, we break apart the Virtual Chassis (by disconnecting/disabling the VC Ports).
3. With the backup device completely isolated, we upgrade the software on the backup device and reboot it. The backup device will keep a copy of the original network configuration.
4. After the upgraded backup comes online, we shift server traffic from the primary device to the backup device. Once the backup is handling the network load, we upgrade and reboot the primary device (after isolating the former master routing engine).
5. After the primary device comes online, we shift traffic back to the primary device.
6. Finally, we re-enable the Virtual Chassis links between the two devices to re-create the Virtual Chassis pair running the new software version.

You may refer to the following documentation for a step-by-step guide: https://www.juniper.net/documentation/us/en/software/nce/nce-171-qfx-vc-upgade/topics/topic-map/nce-171-qfx-vc-upgrade.html

2023-10-07

4/7/26 - grammar improvement.