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Understanding Virtual Chassis Fabric Configuration

Virtual Chassis Fabric Setup

You must setup your VCF using one of the following options:

• Autoprovisioned Virtual Chassis Fabric Configuration
• Preprovisioned Virtual Chassis Fabric Configuration
• Nonprovisioned Virtual Chassis Fabric Configuration

Autoprovisioned Virtual Chassis Fabric Configuration

Autoprovisioned configuration allows you to “plug and play” leaf devices into a VCF after minimal initial configuration.

The minimal configuration requirements for autoprovisioning a VCF include setting the configuration mode to autoprovisioned and explicitly identifying the spine devices in your VCF by serial number. After this minimal configuration is complete, all supported devices—supported devices are either devices that have been zeroized or devices in factory default mode that have never been configured into a Virtual Chassis or VCF—are automatically added to the VCF as leaf devices when they are cabled to spine devices using supported 10-Gbps SFP+ ports or 40-Gbps QSFP+ ports. The Virtual Chassis ports (VCPs) are created automatically. Other parameters such as fabric and mixed mode are automatically detected and set.

A spine device in an autoprovisioned configuration should be configured into fabric mode before being interconnected into a VCF. A spine device in an autoprovisioned VCF must also have the same mixed mode setting as other member devices in the VCF. You should configure your spine device into fabric mode and, if necessary, mixed mode before interconnecting it into the VCF.

A leaf device in an autoprovisioned configuration is rebooted to complete the fabric mode configuration when it is interconnected into a VCF without being set into fabric mode. The leaf device is also rebooted if the device needs to be configured into or out of mixed mode to participate in the VCF. You can avoid the downtime that accompanies the reboot of the leaf device by setting the leaf device into fabric mode and into or out of mixed mode before interconnecting it into the VCF.

Preprovisioned Virtual Chassis Fabric Configuration

In a preprovisioned configuration, you deterministically control the devices in your VCF by associating each device’s serial number to a member ID and role.

The advantage of configuring a VCF using a preprovisioned configuration is that you can explicitly control which devices are added to your VCF, and in what roles. VCP configuration, notably, occurs automatically when two devices that have been configured into fabric mode (and mixed mode, if applicable) are interconnected by a supported 10-Gbps SFP+ port or a 40-Gbps QSFP+ port after the preprovisioned configuration is defined.

The disadvantage of using a preprovisioned configuration is that the configuration process is more manual then the autoprovisioned configuration process.

Nonprovisioned Virtual Chassis Fabric Configuration

Caution: We discourage nonprovisioned VCF configuration. You can configure all aspects of a VCF using autoprovisioned or preprovisioned configuration. Nonprovisioned VCF configuration should only be used by VCF experts in specialized scenarios.

A nonprovisioned VCF is the default method for creating a VCF; it is the configuration mode used when a VCF has not been configured into autoprovisioned or preprovisioned mode.

In a nonprovisioned VCF, member roles are determined by a mastership election algorithm. The first value checked by the mastership election algorithm is the mastership priority value. The switches with the highest mastership priority values assume the master and backup Routing Engine roles in a VCF.

If two or more devices have the same mastership priority value and are candidates for the Routing Engine role, the mastership election algorithm uses other parameters to determines which device is elected as the Routing Engine. See Understanding Virtual Chassis Fabric Components.

The default mastership priority value for all devices is 128. You should always configure two QFX5100 switches acting as spine deviceswith the highest mastership priority to ensure the Routing Engine role is assigned to a spine device..

In a nonprovisioned VCF, you must manually configure every VCP.

Configuration File Management in a VCF

You configure a VCF by logging onto the master Routing Engine and making configuration changes. See the next section for information on logging into a VCF.

The configuration file that is modified when you are on the master Routing Engine is automatically shared with all other devices in the VCF when it is committed. Each device stores it’s own copy of the configuration file.

Logging into a Virtual Chassis Fabric

The recommended method of logging into a VCF is through the use of a Virtual Management Ethernet (VME) interface. The VME interface is a logical interface representing all of the out-of-band management ports on the member devices. When you connect to the VCF configuration using the VME interface’s IP address, the connection is always redirected to the management port on device in the master Routing Engine role. The VME interface is not tied to a device, so it can always be used to log in to the VCF even after the master Routing Engine changes. We recommend cabling the management ports—an me or em interface—on each Routing Engine in your VCF to support the VME interface.

If you log in to the console port of any member device in a VCF, your session is automatically redirected to the device acting in the master Routing Engine role.

Understanding Interface Numbering

Interfaces in Junos OS are specified as follows:

type-fpc/pic/port

A VCF applies this convention as follows:

• type—The interface type.
• fpc—Flexible PIC Concentrator. In a VCF, the fpc is the member ID of the switch. For instance, the fpc of member 16 in the VCF is 16.
• pic—the number of the PIC (Physical Interface Card) on the member device.
• port—the port number.

For more detailed information on interface numbering, see Understanding Interface Naming Conventions.