Understanding Software Upgrades in a Virtual Chassis
This topic discusses software upgrades on EX Series and QFX Series Virtual Chassis, except EX8200 Virtual Chassis. For information on software upgrades on an EX8200 Virtual Chassis, see Understanding Software Upgrades in an EX8200 Virtual Chassis. For information on software upgrades on a Virtual Chassis Fabric (VCF), see Understanding Software Upgrades in a Virtual Chassis Fabric.
In a Virtual Chassis, each member switch must be running the same version of Juniper Networks Junos operating system (Junos OS) that supports Virtual Chassis. You can install a new Junos OS release on the entire Virtual Chassis or on individual members in the Virtual Chassis by using the same CLI command that you use to install Junos OS on standalone switches—the request system software add command.
In a mixed Virtual Chassis, the member switches must also be running the same version of Junos OS, but you might need to specify multiple Junos OS images when manually or automatically upgrading a mixed Virtual Chassis. For example, for the same Junos OS release, an EX4200 switch runs a different Junos OS image than an EX4500 or EX4550 switch, or an EX4300 switch runs a different Junos OS image than a QFX5100 switch in a QFX5100 Virtual Chassis. You can upgrade all member switches simultaneously by specifying a path to multiple Junos OS images in the same request system software add command.
Some different switch platforms can run the same Junos OS image. For example, you do not need to use multiple Junos OS images when updating a Virtual Chassis with a combination of EX4500 and EX4550 switches, or a Virtual Chassis with a combination of QFX3500 and QFX3600 switches.
You can also use the following features to upgrade software on members of a Virtual Chassis:
Automatic Software Updates
You can use the automatic software update feature on a non-mixed or mixed Virtual Chassis to automatically update the Junos OS version on member switches as you add them to the Virtual Chassis. See Understanding Automatic Software Update on Virtual Chassis Member Switches for more information.
If you are not configuring the automatic software update feature, we recommend that you update the new member switch to the version of Junos OS running on the Virtual Chassis before adding the member switch to the Virtual Chassis.
Nonstop Software Upgrade
You can also use nonstop software upgrade (NSSU) to upgrade Junos OS on all members of a Virtual Chassis for EX Series and QFX Series Virtual Chassis that support NSSU. NSSU provides an orderly upgrade of each member of the Virtual Chassis and takes advantage of graceful Routing Engine switchover, nonstop active routing, and link aggregation to minimize traffic disruption during the upgrade.
For more information about NSSU, see:
(For legacy EX Series switches in a Virtual Chassis) Upgrading Software Using Nonstop Software Upgrade on EX Series Virtual Chassis and Mixed Virtual Chassis (CLI Procedure)
If NSSU is not supported to upgrade a Virtual Chassis from the currently-installed release to the release you need, refer to procedures like these for some guidance:
Two-Member QFX Series Virtual Chassis Upgrade Procedure, a network configuration example on how to manually upgrade a two-member QFX Series Virtual Chassis when NSSU isn’t available.