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Configuring the Number of SMET Nexthops

Junos OS uses the EVPN Type 6 selective multicast Ethernet tag (SMET) route message to support the following:

  • External multicast sender (IGMP proxy)—EVPN Type 6 route messages are used within the EVPN network. The ingress PE device translates the IGMP message to an EVPN Type 6 route message and the egress PE device translates the EVPN Type 6 route messsage back to an IGMP message.

  • Inter-VLAN multicast—EVPN Type 6 route messages are used to create a PIM states on a PE device with an IRB interface. This allows multicast traffic to be sent across VLANs.

  • Selective multicast forwarding—The EVPN Type 6 route messages are used to distribute the routing information indicating a PE device’s interest for a multicast group.

The information in the EVPN Type 6 route message are used to build a list of SMET next hops, which can be used to selectively replicate and forward multicast packets. SMET next hop is a list of outgoing interfaces (OIFs) identifying the interested PEs . Multicast groups are mapped to SMET next hops. If multicast groups that have the same set of interested PEs, they can share a SMET next hop. The number of SMET nexthops defaults to 10,000 and can be increased by configuring the smet-nexthop-limit option. When a device reaches the SMET nexthop limit, the device will start using inclusive multicast forwarding for multicast traffic.

Devices in the network that do not support snooping or cannot send EVPN Type 6 route messages are always included in the SMET next hop. This practice ensures those devices that do not support EVPN Type 6 route messages will be able to receive multicast traffic.

To configure the number of SMET nexthops, you can use the following statement:

User@PE1# set forwarding-options multicast-replication evpn smet-nexthop-limit nexthop range.

In some cases, you may want to bypass selective multicast forwarding and send multicast traffic to all devices. If you wish to send multicast traffic to a group, you can list the multicast group address with the following statement

User@PE1# set multicast-snooping-options flood-groups [ip-addresses]

Note:

OSPF messages, which use multicast addresses for communication, are automatically included in the multicast snooping forwarding table.

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