Understanding Automatic Software Update on Virtual Chassis Member Switches
The automatic software update feature automatically updates the Juniper Networks Junos operating system (Junos OS) version on prospective member switches as they are added to a Virtual Chassis configuration of Juniper Networks EX4200 Ethernet Switches so the new member switch immediately joins the Virtual Chassis configuration and is put in the active state.
For a standalone EX4200 switch to join an existing Virtual Chassis configuration, it must be running the same version of Junos OS that is running on the Virtual Chassis master. When the master in a Virtual Chassis configuration detects that a new switch has been added to the configuration, it checks the software version on the new switch. If the software version on the new switch is not the same as the version running on the master, the master keeps the new switch in the inactive state. If you have not enabled the automatic software update feature, you will have to manually install the correct software version on each prospective member switch as it is added to the Virtual Chassis configuration.
