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irb (EVPN Multicast Replication)

Syntax

Hierarchy Level

Description

Enable one of the supported integrated routing and bridging (IRB) multicast modes in an EVPN-VXLAN network.

The EVPN IRB multicast mode options are mutually exclusive. You can enable only one of these modes at a time, and you must configure the same mode on all devices in the network that process multicast traffic. If you don't select one of the mode options described here, the default EVPN IRB multicast behavior is the same as the behavior of the local-remote option.

Only the local-remote, oism, and enhanced-oism modes support forwarding with selective multicast Ethernet tag (SMET) routes (EVPN Type 6 routes).

Note:

In the Options section, we usually list the available options in alphabetical order. However, here we describe the oism option before the enhanced-oism to introduce background on the optimized intersubnet multicast (OISM) feature. Then we list the enhanced-oism option to summarize the differences if you use the enhanced-oism option instead, which enables an enhanced version of OISM.

Options

local-only

Use this mode with an edge-routed bridging (ERB) overlay, also known as a collapsed IP fabric. In this mode, the PFE on the leaf devices in the fabric performs local multicast routing at the fabric edge. The spine devices, also called lean spines, primarily act as IP transit devices for the fabric.

local-remote

Use this mode with a centrally-routed bridging (CRB) overlay, also known as a two-layer IP fabric. In this mode, the spine devices in the fabric centrally route the multicast traffic between VLANS. The spine devices forward the routed VLAN traffic into the EVPN core toward interested receivers. The spine devices use a PIM designated router (DR) to avoid duplicating packets into the core. The leaf devices forward multicast traffic received on a VLAN to their receivers on that VLAN.

This is the default EVPN IRB multicast mode if you don't configure any of the options at the [edit forwarding-options multicast-replication evpn irb] hierarchy level.
oism

Use this mode with an ERB overlay to support routing multicast traffic inside the fabric as well as to and from external devices. This mode implements OISM according to the IETF draft https://tools.ietf.org/html/draft-ietf-bess-evpn-irb-mcast. In this mode, the leaf devices operate in local-remote mode like in a CRB overlay design, while at the same time, the device performs local multicast routing. This mode enables the original regular OISM mode that uses a symmetric bridge domains (VLANs) OISM model. The symmetric bridge domains model means that with regular OISM mode, you must configure all revenue bridge domains (VLANs) symmetrically on all OISM devices.

OISM also supports:

  • Selective forwarding on the source VLAN.

  • Routing multicast traffic through an external PIM domain.

Note:

You can alternatively enable the enhanced version of OISM, if all of the OISM devices in your network support the enhanced OISM mode option. See the enhanced-oism option description (next) for information on when you might use that option instead of this original OISM mode option.
enhanced-oism

This mode implements an enhanced version of OISM for EVPN multicast with ERB overlays. Enhanced OISM doesn't require you to configure all revenue bridge domains (VLANs) in the network on all OISM devices. On each device, you can configure only the revenue VLANs the device hosts. As a result, we say this mode uses an asymmetric bridge domains (VLANs) model. On supported devices, this mode enables OISM to scale well when your network has leaf devices that host larger numbers of different VLANs.

This mode has some operational differences and small configuration differences to support the enhanced OISM asymmetric bridge domains model. As a result, if you enable OISM, all OISM devices in the network must use the same OISM mode option, either oism or enhanced-oism.

You can choose to use the enhanced-oism option instead of the regular oism option if all OISM devices in the network support enhanced OISM. In that case, you might want to use enhanced OISM when:

  • Your network has a large number of revenue bridge domains (VLANs), and resources might be strained on some devices to configure all the VLANs there.

  • Your network has a large number of disjointed bridge domains (VLANs) in the network (different devices host different sets of VLANs).

  • On OISM devices in your network, you don't have policies configured that are based on the source MAC address of the packets. If you do have source MAC address policies, use the oism option in your network instead.

Note:

You should use regular OISM instead of enhanced OISM if your network needs to pass multicast packets with stringent requirements for decrementing the time-to-live (TTL) field. The enhanced OISM model inherently has a limitation where packets with TTL=1 will not reach receivers on devices that are not multihoming peers of the source device. Regular OISM forwards source traffic on the source VLAN and doesn't decrement the TTL value for destinations on the same VLAN.

See Summary of Enhanced OISM Differences for details.

Enhanced OISM also supports:

  • Selective forwarding on the source VLAN.

  • Routing multicast traffic through an external PIM domain.

Required Privilege Level

interface—To view this statement in the configuration.

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

Release Information

oism option introduced in Junos OS Release 21.2R1.

enhanced-oism option introduced in Junos OS Release 23.4R1.

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