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Configuring a Nonprovisioned Virtual Chassis Fabric


Configure your Virtual Chassis Fabric (VCF) using autoprovisioning or preprovisioning unless you have a compelling reason to use nonprovisioned configuration. You can configure all aspects of a VCF using autoprovisioned or preprovisioned configuration. The process for autoprovisioning your VCF is described in Autoprovisioning a Virtual Chassis Fabric and the process for preprovisioning your VCF is described in Preprovisioning a Virtual Chassis Fabric.

Nonprovisioned VCF configuration is highly discouraged. Nonprovisioned VCF configuration should only be used by VCF experts in specialized scenarios.

A nonprovisioned VCF is the configuration mode used when a VCF has not been configured into autoprovisioned or preprovisioned mode.

In a nonprovisioned VCF, you configure the device roles by setting the primary-role priority value of each device. If no primary-role priority values are set, a algorithm process runs and selects the role for each device.

You must manually configure all Virtual Chassis ports (VCPs) in a nonprovisioned VCF. The automatic VCP conversion feature, which automatically configures supported 10-Gbps SFP+ links and 40-Gbps QSFP+ links into VCPs on autoprovisioned and preprovisioned VCFs, is not supported on nonprovisioned VCFs.

Update all devices to the same version of Junos OS that supports VCF. See Installing Software Packages on QFX Series Devices or Installing Software on an EX Series Switch with a Virtual Chassis or Single Routing Engine (CLI Procedure).


QFX5100 switches running a Junos OS image that includes “-qfx-5-” in the software package filename must be upgraded to a package filename that includes “-qfx-5e-” before being added to a QFX5110 Virtual Chassis. See Upgrading a QFX5100 Switch with a USB Device to Join a QFX5110 Virtual Chassis or Virtual Chassis Fabric.

To configure a nonprovisioned VCF:

  1. Power on the devices.
  2. Configure each individual device into fabric mode. If needed for a mixed VCF, configure the devices into mixed mode.

    Reboot each device to complete this configuration step.

    If you are configuring a non-mixed VCF:

    If you are configuring a mixed mode VCF:


    A device whose fabric or mixed mode setting is improperly set cannot join a mixed VCF. You can check the mode settings using the show virtual-chassis mode command.

    We recommend setting the fabric and mixed mode settings before interconnecting your devices into a VCF to avoid the following issues:

    • Incurring downtime as the devices reboot to commit the mixed mode or fabric settings.

    • Manually correcting potential issues related to VCF formation because the device did not immediately join the VCF.

    We strongly recommend configuring the mixed and fabric settings before you interconnect a device into a VCF. You can, however, use the request virtual-chassis mode fabric local or request virtual-chassis mode mixed local commands to set a device into fabric or mixed mode after you have interconnected your VCF.

  3. After the device reboots are complete, cable your spine devices to your leaf devices using supported interfaces that can be used as VCPs.
  4. (Recommended) Configure a virtual management Ethernet (VME) interface for management of the VCF configuration:

    A VME accesses the device in the primary Routing Engine role using a management port, so cable management port em0 or em1 on each spine device in your VCF so the VME is available regardless of which spine device assumes the primary Routing Engine role. See Connecting a QFX Series Device to a Management Console

  5. Configure the desired interfaces into Virtual Chassis ports (VCPs):

    The show virtual-chassis vc-port must be issued on the ports at both ends of the link in order for that link to be configured into a VCP link.

  6. Enter the show virtual-chassis command to confirm that the VCPs are operational and to learn the member ID of each member device in your VCF.

    If you want to change the member ID that has been assigned to a member device, use the request virtual-chassis renumber command.

  7. (Optional) Configure the primary-role priority for each member device:

    In a nonprovisioned VCF, member roles are determined by a primary-role election algorithm. The first value checked by the primary-role election algorithm is the primary-role priority value. The two devices with the highest primary-role priority values assume the primary and backup Routing Engine role, which must be supported spine devices in a VCF. All other devices assume the linecard role.

    In a QFX5100 VCF, QFX5100 switches assume the Routing Engine role, regardless of primary-role priority settings. QFX5100 switches can also assume the linecard role. QFX3600, QFX3500, and EX4300 switches always assume the linecard role in a mixed QFX5100 VCF, regardless of the primary-role priority settings.

    In a QFX5110 VCF, spine devices must be QFX5110-32Q switches, and can also assume the linecard role as spine or leaf devices. In a QFX5110 VCF with QFX5100 switches, any QFX5100 members and other QFX5110 members must be leaf devices and assume the linecard role.


    A spine device that isn’t selected as primary or backup Routing Engine assumes the linecard role. The spine devices should still be configured with a higher primary-role priority value than the leaf devices to assure a spine device assumes the Routing Engine role when the primary or backup Routing Engine fails.

    If two or more devices have the same primary-role priority value and are candidates for the Routing Engine role, the primary-role election algorithm uses other parameters to determines which device is elected into the Routing Engine role. See Understanding How the Primary in a Virtual Chassis Is Elected.

    A device with a primary-role priority of 0 never assumes the primary or backup Routing Engine role.

    For instance, to configure the primary-role priority for member devices 0 through 19 in your VCF.

  8. Install the VCF feature licenses.

    For a VCF deployment, two license keys are recommended for redundancy—one for the device in the primary Routing Engine role and the other for the device in the backup Routing Engine role.

    To purchase a feature license for VCF, contact your Juniper Networks sales representative ( The Juniper sales representative will provide you with the feature license files and license keys. You will be asked to supply the chassis serial number of your switch; you can obtain the serial number by running the show virtual-chassis command.

    After obtaining the licenses, follow the instructions in Generating License Keys.