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Understanding Software Upgrades in a Virtual Chassis Fabric


This topic provides an overview of software upgrades on Virtual Chassis Fabric (VCF).

It contains the following sections:

Virtual Chassis Fabric Software Basics

VCF is initially supported in Junos OS Release 13.2X51-D20. All devices in a VCF must be running the same version of Junos OS that supports VCF.

At initial VCF configuration, you should update all devices to the same Junos OS release before inteconnecting them into a VCF.

When you are adding a device to an existing VCF, you should update the Junos OS release on the new device to the Junos OS release running in the VCF before interconnecting it into the VCF. Updating the Junos OS on the device before interconnecting it helps ensure the device is gracefully added to the VCF, without the downtime that is required to reboot the device after an automatic software update or the troubleshooting that is required if the device isn’t added to the VCF due to mismatched software releases.

Before you interconnect a device into a VCF, you should upgrade the software on the device being added to the VCF to the version of Junos OS running on the VCF.

Nonstop Software Upgrade (NSSU)


NSSU is not supported on a QFX5110 VCF.

Nonstop software upgrade (NSSU) enables you to upgrade the software running on all member devices in a VCF with minimal network traffic disruption during the upgrade.

NSSU upgrades the software on each device individually while all other devices continue normal operations.

For additional information on NSSU in a VCF, see Understanding Nonstop Software Upgrade on a Virtual Chassis Fabric.

Automatic Software Update

Automatic software update automatically upgrades the Junos OS running on a device joining a VCF to the version of Junos OS running on the VCF at the moment the new device is cabled into the VCF.

Automatic software update is enabled using the set virtual-chassis auto-sw-update statement.


A QFX5100 switch running a Junos OS software image with “-qfx-5-” in the package filename must first be upgraded to a Junos OS software image with “-qfx-5e-” in the package filename before it can be added to a QFX5110 Virtual Chassis or VCF. The automatic software update process cannot update a switch from a “-qfx-5-” image to a “-qfx-5e-” image. See Upgrading a QFX5100 Switch with a USB Device to Join a QFX5110 Virtual Chassis or Virtual Chassis Fabric.

After a QFX5100 switch is installed with a “-qfx-5e-” Junos OS software image, the automatic software update process can successfully update the switch automatically with a different version of a “-qfx-5e-” Junos OS image to match the other members in the Virtual Chassis or VCF.

Traditional Software Upgrade

You can upgrade software on a VCF using the traditional method of upgrading software for Junos OS by logging onto the master Routing Engine and using the request system software add command to initiate the upgrade on a non-mixed VCF or the request system software add set [package-name package-name ...] to initiate the upgrade on a mixed VCF, where package-name is the path to an image for one device family.

When you upgrade Junos OS on a VCF using the traditional software upgrade, the entire system is down until the upgrade is complete.