Juniper EX4200 Hardware Manual page 227

Virtual Chassis) Ensure that the correct version of Junos OS is or will be installed on the new member
switch by performing either of the following tasks:
Enable automatic software update on the Virtual Chassis. See Configuring Automatic Software Update
on Virtual Chassis Member Switches. The Virtual Chassis will automatically update the software on the
replacement switch in a later step when it is interconnected and recognized as part of the Virtual
Chassis. The replacement switch does not require any action in this case for this step.
Install the version of Junos OS running on the Virtual Chassis onto the new member switch before
interconnecting it into the Virtual Chassis. For EX series switches, see Installing Software on an EX
Series Switch with a Virtual Chassis or Single Routing Engine (CLI Procedure), or for QFX Series switches,
see Software Installation and Upgrade Overview and Installing Software Packages on QFX Series Devices.
In this case, at the end of this step, the replacement switch will be running with the new version of
the software and should have the factory default configuration.
CAUTION:
and QFX5100 switches if they are running the same Junos OS image that includes
"-qfx-5e-" in the software package filename (from the Junos OS Software Center).
If the switch you are replacing in a QFX5110 Virtual Chassis is a QFX5100 switch
that you previously installed with a "-qfx-5-" Junos OS image file, you must
upgrade the replacement switch to a "-qfx-5e-" image instead before inserting it
into the QFX5110 Virtual Chassis. See Upgrading a QFX5100 Switch with a USB
Device to Join a QFX5110 Virtual Chassis or Virtual Chassis Fabric. The automatic
software update feature can't update a "-qfx-5-" image to a "-qfx-5e-" image.
5. Connect one link from the replacement member switch to the Virtual Chassis as follows, depending
on which type of ports you are using:
If you are interconnecting a switch using dedicated Virtual Chassis Ports (VCPs), connect one dedicated
VCP on the replacement member switch to a dedicated VCP on another member switch in the Virtual
Chassis.
If you are interconnecting a switch using optical ports configured as VCPs:
On the replacement switch, configure the optical ports that you are using to connect to the Virtual
Chassis as VCPs. (You should also configure the optical ports on the existing member switches in the
Virtual Chassis where the replacement member switch will be connected, if they are not already
configured.) To configure an optical port as a VCP:
user@switch> request virtual-chassis vc-port set pic-slot 1 port port-number
Connect one configured optical port VCP on the replacement switch to a configured optical port
VCP on another member switch in the Virtual Chassis.
You can only set up a QFX5110 Virtual Chassis with both QFX5110
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