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Hierarchy Level


In a QFabric system, a hash function is used to select an Interconnect device to forward traffic between two ingress switches, which are called Node devices. Since this hash function is performed on all Interconnect devices, it is possible for redundant multicast streams to flow through one Interconnect device, making that Interconnect device a potential single point of failure for the redundant flows. Some operations, such as financial transactions, require redundant data flows to use different Interconnect devices to avoid point-of-failure data loss. To enforce this in a fabric, you can create a flow group for multicast or unicast traffic from a particular ingress switch. In a flow group, switches are forced to use different, specified Interconnect devices to forward redundant traffic.


The following rules apply to QFabric system flow control:

  • A Node device can belong to only one flow group.

  • A fabric can contain up to four flow groups.

  • Node devices in flow groups can only use the defined Interconnect devices in their flow groups unless all defined Interconnect devices fail. In case of failure, the flow group checks for Interconnect devices with preference set to normal—this includes all Interconnect devices in the default group and any Interconnect devices you specifically set to preference normal.

The following example creates a flow group. The name of the flow group, test1, is configured first. Next, the Node device TA3713480203 is configured, and the Interconnect device IC-P6603-C is configured last.

The following example overrides the software settings the flow group test1 Node device TA3713500307 was assigned by the software for Interconnect device IC-P6601-C. Node device TA3713500307 has its preference for Interconnect device IC-P6601-C set to never by the software, meaning that Node device TA3713500307 can never use Interconnect device IC-P6601-C. You can change this preference so that Interconnect device IC-P6601-C can be used by Node device TA3713500307 if the specifically-configured Interconnect devices all fail. You use the preference option of the flow-groups configuration statement to set Interconnect device IC-P6601-C preference to normal for Node device TA3713500307.

To configure the preference setting for a Node device to use a particular Interconnnect device, you first select the Node device, then specify the Interconnect device, and finally specify the preference option:


To add a TOR to multiple flow groups: set fabric resources node-device TOR-B interconnect-device IC-A preference HIGH To configure a TOR to use an Interconnect device from a different flow group if none in the same flow group are available: set fabric resources node-device TOR-B interconnect-device IC-A preference NORMALTo increase the priority of default-flowgroup Interconnect devices for a specific TOR: set fabric resources node-device TOR-A interconnect-device ALL_ICS preference HIGH To configure default-flowgroup TORs to never use a particular Interconnect device: Set fabric resources node-device ALL_TORS interconnect-device IC-A preference NEVER


node-device node-device-name

Specify a QFabric system ingress Node switch by device name or alias in the QFabric system.

interconnect-device interconnect-device-name

Specify a QFabric system Interconnect device name.

preference preference

Overrides the algorithm results that assign preference to Node devices to use particular Interconnect devices. You can set preference values for these devices to normal, high, or never. (See Example: Creating a QFabric Flow Group for more details on setting preference values and their meanings.

Required Privilege Level

admin—To view this statement in the configuration.

admin-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 14.1X53-D15.