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oism (Multicast Snooping Options)


Hierarchy Level


Set optimized inter-subnet multicast (OISM) options. You can use OISM to optimize multicast traffic flow in an EVPN-VXLAN fabric.



Set the Routing Engine to immediately install (*,G) multicast routes (upon receiving an EVPN Type 6 route) on the Packet Forwarding Engine for all of the revenue VLANs in the routing instance.

Without this option, the device prioritizes saving resources on the Packet Forwarding Engine by not installing multicast routes until the multicast traffic arrives. The default behavior avoids issues with scaling on lower-end devices.

If you configure this option, the device ensures the Packet Forwarding Engine has multicast routing information available before any multicast traffic arrives. This option minimizes packet loss at the onset of a multicast flow. However, the device consumes extra Packet Forwarding Engine resources for routes that are not even being used yet (and might never be used). As a result, when you configure this option, you trade off taking up the extra Packet Forwarding Engine resources to improve network latency.

You set this option globally in the default-switch routing instance. The option acts only on VLANs associated with a Layer 3 virtual routing and forwarding (VRF) instance with OISM enabled.


Always configure this option with OISM on switches in the QFX10000 line. These switches easily operate at scale and multicast traffic flows well with this option set. Without this option, QFX10000 switches have an issue with mesh group handling and don't properly install the multicast routes. We don't recommend setting this option with OISM on switches in the QFX5000 line. Consider this option on those switches only if you have very stringent latency requirements and can trade those off latency against supporting higher scaling.

Required Privilege Level

routing—To view this statement in the configuration.

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

Release Information

Statement introduced in Junos OS Release 21.2R1.