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Hierarchy Level


Optionally specify a member of a VCF to be a root node for creating the shared multicast distribution trees (MDTs) used in forwarding broadcast, unknown unicast, and multicast (BUM) traffic within the VCF. To configure this option, the VCF must be configured as auto-provisioned or preprovisioned.


This option only affects MDTs used for directing traffic internally between member nodes of the VCF, and does not affect how BUM traffic is managed on the network outside the VCF.

Setting this option affects BUM traffic routing behavior within the VCF by changing how VCF MDT trees are created. By default, if this option is not configured for any VCF members, every member switch builds an MDT with itself as the root. When this option is configured for one or more VCF members, MDTs are only created with the specified member or members as root nodes. The number of trees created corresponds to the configured number of root nodes.

If you want to use this option in a VCF, we recommend configuring all the spine devices in the VCF (regardless of the role—Routing Engine or linecard), and only spine devices, as fabric tree roots. Configuring multiple spine devices as fabric tree roots prevents inadvertently reverting to the default behavior if a spine member becomes unavailable. Avoiding leaf members as fabric tree roots helps to prevent traffic interruption during load rebalancing when a leaf node goes offline or is reset.

See Understanding Traffic Flow Through a Virtual Chassis Fabric for more information about how this option affects traffic flow.

Required Privilege Level

system—To view this statement in the configuration.system-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 14.1X53-D35.