OISM with a default IRB routing instance

You can configure optimized intersubnet multicast (OISM) using a default L3 integrated routing and bridging (IRB) routing instance. We support this feature with:

• IPv4 underlay peering in the EVPN-VXLAN network.
• IPv4 multicast traffic with IGMPv2/v3 and IGMP snooping.

With a default L3 routing instance, you configure L3 OISM parameters at the global level instead of at a particular virtual routing and forwarding (VRF) instance level. For example, configure the L3 EVPN protocol statements at the [edit protocols evpn ?] hierarchy level instead of at the [edit routing-instances name protocols evpn ?] hierarchy level. Also, to prevent routing loops when you use a default routing instance, you must also set a forwarding table export policy that includes the install-nexthop except overlay-vxlan-interfaces policy option.