This article provides information about the general Virtual Chassis configuration in EX/QFX switches.

This helps you to configure Virtual Chassis in EX/QFX model switches:

• Verify the members that are going to be merged for virtual chassis are under same version.
• Understand the type of VC port for the models (Default/Configured, Dedicated, Auto Configured) before establishing the VC link.

This solution includes the following topics:

• Non-mixed VC configuration (Same model devices)
• VC port configuration

The below example helps in configuring VC with 4 members (Master, Backup, Line card, Line card)

1. Verify all the members are running the same JUNOS Version:

root@switch> show version
 

2. Specify that you want to create a preprovisioned Virtual Chassis configuration:

      [edit virtual-chassis]
      user@switch# set preprovisioned

3. Configure each member role either RE or Line-card & members are identified by Serial Number & Member-ID:

   [edit virtual-chassis]
   user@switch# set member 0 serial-number <serial-number> role routing-engine
   user@switch# set member 1 serial-number <serial-number> role routing-engine
   user@switch# set member 2 serial-number <serial-number> role line-card
   user@switch# set member 3 serial-number <serial-number> role line-card

NOTE: In a two-member EX Series Virtual Chassis configuration, you must assign the routing-engine role to each router. The routing-engine role enables the router to function either as the primary router or backup router of the Virtual Chassis.

4.  To configure uplink ports as VCPs to interconnect the member switches (Run on each switch)

user@switch> request virtual-chassis vc-port set pic-slot 1 port 0
user@switch> request virtual-chassis vc-port set pic-slot 1 port 1

NOTE: if the switch is having dedicated VCPs it doesn't require any VC port configuration

https://www.juniper.net/documentation/us/en/software/junos/virtual-chassis-qfx/topics/task/virtual-chassis-ex4300-configuring.html