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oism (Multicast Snooping Options)


Hierarchy Level


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


The functions of the conserve-mcast-routes-in-pfe option and the install-star-g-routes option are mutually exclusive, so you can use only one or the other of these options in a routing instance. See the descriptions of these options below for details on when to use each option.



(ACX Series routers, QFX5130 switches, and QFX5700 switches) Conserve Packet Forwarding Engine (PFE) multicast route table space on the device by not installing Layer 2 (L2) multicast snooping (*,G) and (S,G) states in the PFE when the device receives EVPN Type 6 routes. The device uses only the Layer 3 (L3) multicast routes in the PFE to forward multicast traffic. Without this option, these devices install L2 multicast group entries in the PFE for all OISM revenue bridge domain VLANs and the SBD.

We require you configure this option on ACX Series routers, QFX5130 switches, and QFX5700 switches in EVPN-VXLAN networks running OISM in the server leaf or border leaf role. With this option, these devices conserve PFE table space by installing only the L3 multicast routes; they avoid installing L2 multicast snooping routes.

QFX5130 or QFX5700 switches running as standalone AR replicators with OISM conserve PFE multicast snooping route table space by default. As a result, don't use this option when you configure those switches in the assisted replication (AR) replicator role with OISM.

See OISM and AR Scaling with Many VLANs for more information on using this option.


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

Without this option, the device prioritizes saving resources on the PFE 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 PFE 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 PFE 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 PFE resources to improve network latency.

This option acts only on VLANs associated with a Layer 3 virtual routing and forwarding (VRF) instance with OISM enabled.

Set this option:

  • Globally if you configure EVPN in the default-switch instance.

  • In the MAC-VRF instances if you configure EVPN in instances of type mac-vrf.

We require that you configure install-star-g-routes with OISM on the QFX10000 line of switches, QFX5130-32CD switches, and QFX700 switches when you configure those devices with AR in the AR replicator role.

In releases prior to Junos OS and Junos OS Evolved Release 23.4R1, you must also configure the install-star-g-routes option on the following devices when you configure them as OISM server leaf or border leaf devices:

  • The QFX10000 line of switches.

  • PTX10001-36MR, PTX10004, PTX10008, and PTX10016 routers.

Starting in Junos OS and Junos OS Evolved Release 23.4R1, we no longer require this option when you configure those devices as OISM server leaf or border leaf devices.

We don't recommend setting this option other than in the use cases mentioned above. Consider this option only if you have very stringent latency requirements and can trade off higher scaling to achieve better network latency.

For more information about how this option works, see Latency and Scaling Trade-Offs for Installing Multicast Routes with OISM (install-star-g-routes Option) .

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 and Junos OS Evolved 22.1R1.

conserve-multicast-routes-in-pfe option introduced in Junos OS Evolved Releases 22.4R2 and 23.1R1.