forward-on-source-bridge-domain

Syntax

Hierarchy Level

Description

Enable enhanced optimized intersubnet multicast (OISM) to forward multicast data traffic on the multicast source VLAN for traffic that matches the provided forwarding policy (or policies).

When you configure enhanced OISM, you allocate an OISM supplemental bridge domain (SBD) for each Layer 3 (L3) virtual routing and forwarding (VRF) instance. You also configure the tenant VLANs on each OISM device for the hosts the device serves. By design, even if the destination OISM device hosts the multicast source VLAN, enhanced OISM routes the multicast traffic from the source VLAN to the SBD toward the remote OISM devices. The each remote OISM device locally routes the traffic from the SBD to the destination tenant VLAN.

The enhanced OISM route-to-SBD model enables efficient multicast data transfer in networks with a large number of tenant VLANs hosted by different OISM devices. However, when enhanced OISM routes multicast packets to the SBD and then to the destination VLAN, the packet time-to-live (TTL) count is decremented more than once. As a result, in that case source packets with TTL=1 won't reach the receivers.

Regular OISM forwards multicast traffic from internal sources on the source VLAN, and the remote devices then forward or route the traffic to the destination VLAN. As a result, regular OISM can successfully deliver source packets with TTL=1 to the receivers. However, regular OISM doesn't scale well in environments with many tenant VLANs, because that model requires you to configure all tenant VLANs on all OISM devices (even if a device doesn't have hosts on some of the VLANs).

If you want to use enhanced OISM instead of regular OISM with multicast source packets that have TTL=1, you can use the forward-on-source-bridge-domain statement to ensure those packets reach the subscribed receivers. This statement applies exception policies on the device to forward on the source VLAN (instead of routing to the SBD) for specific multicast groups, or sources and groups. You configure routing policies to match the multicast groups [(*,G)] or multicast sources and groups [(S,G)] for which you want the device to forward multicast traffic on the source VLAN. This statement essentially causes enhanced OISM devices to use the regular OISM forwarding model for particular multicast flows.

You can configure this option only when you use OISM in enhanced OISM mode. To enable enhanced OISM, see the enhanced-oism option at the [edit forwarding-options multicast-replication evpn irb] hierarchy level.

For details on how OISM works and all of the elements you need to configure OISM in an EVPN fabric, see Optimized Inter-Subnet Multicast in EVPN Networks.

For details and configurations examples for this feature, see Enhanced OISM Exception Policy to Forward on Source VLAN Instead of SBD for Packets with TTL=1.

Options

(Required) forward-policy [ forwarding-policy-name ... ]

Routing policy or policies to match multicast groups (or sources and groups) for which the device should forward that multicast traffic on the source VLAN.

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 and Junos OS Evolved Release 25.2R1.