Layer 2 Multicast Configuration

This chapter describes how to configure Layer 2 multicast and provides configuration examples. Layer 2 multicast is used to transmit multicast data at the data link layer. It uses Internet Group Management Protocol (IGMP) snooping to listen to IGMP messages exchanged between an upstream device and hosts attached to the device and then use these messages to create a Layer 2 multicast forwarding table, achieving on-demand multicast data transmission at the data link layer. If both Layer 2 multicast and Layer 3 multicast are configured, ensure the consistency between Layer 2 multicast configurations and Layer 3 multicast configurations. If Layer 2 multicast configurations are inconsistent with Layer 3 multicast configurations, Layer 2 multicast will inherit Layer 3 multicast configurations. As a result, the Layer 2 multicast configurations will become unavailable.

Configuration Precautions for Layer 2 Multicast

Configuring IGMP Snooping: IGMP snooping enables a Layer 2 device to analyze IGMP messages exchanged between a connected Layer 3 device and downstream user hosts and use these IGMP messages to set up mappings between interfaces and multicast MAC addresses. Based on the mappings, the Layer 2 device can then implement on-demand multicast data forwarding at the data link layer.

Configuring Static Layer 2 Multicast: If a user host needs to receive multicast data for a specific multicast group from a router port over a long period of time, static Layer 2 multicast can be used to ensure a stable multicast data transmission. Before configuring static Layer 2 multicast, familiarize yourself with the usage scenario and complete the pre-configuration tasks.

Configuring Layer 2 SSM Mapping: After Source-Specific Multicast (SSM) mapping is configured on a device directly connected to hosts running IGMPv1 or IGMPv2 on a Layer 2 network, these hosts can use IGMPv3 services. Before configuring Layer 2 SSM mapping, familiarize yourself with the usage scenario, complete the pre-configuration tasks, and obtain the data required for the configuration.

Configuring IGMP Snooping Proxy: IGMP snooping proxy enables a device to represent its upstream device and downstream hosts to send IGMP messages to maintain group memberships and use the group memberships to forward multicast traffic, which greatly reduces bandwidth consumption. Before configuring the IGMP Snooping Proxy, familiarize yourself with the usage scenario, complete the pre-configuration tasks, and obtain the data required for the configuration.

Configuring a Multicast VLAN for Specified User VLANs: To enable a Device to request only one copy of multicast data from an upstream device and replicate a separate copy for each user VLAN that is interested in the data, create and associate a multicast VLAN with the user VLANs.

Configuring Layer 2 Multicast Entry Limit: Layer 2 multicast entry limit is a feature used on a Layer 2 network (VLAN or VPLS networking) to prevent bandwidth resources from exceeding the total bandwidth of the aggregation network and ensure service quality for most subscribers.

Configuring Layer 2 Multicast CAC: Layer 2 multicast Call Admission Control (CAC) is a feature used on a VPLS networking to limit the multicast group number and bandwidth that subscribers can utilize and manage the channels of each service provider. This feature prevents bandwidth resources from exceeding the total bandwidth of the aggregation network and ensures service quality for most subscribers.

Configuring the Maximum Number of Invalid Layer 2 Multicast Protocol Packets Allowed on a Multicast Device: Configuring the maximum number of invalid Layer 2 multicast protocol packets allowed on a multicast device helps to locate and rectify faults.

Configuring Fast Restoration for Layer 2 Multicast Services on PWs: To rapidly restore the Layer 2 multicast services on a PW when the PW goes Down and then Up, delay or disable the deletion of the Layer 2 multicast forwarding entries when the PW goes Down.

Configuring Layer 2 Multicast Instances: If users in different VLANs or VSIs request for the same multicast group's data from the same source, configure a Layer 2 multicast instance on the Layer 2 device.

Configuring MLD Snooping: Multicast Listener Discovery (MLD) snooping enables a Layer 2 device to listen to and analyze MLD messages exchanged between a connected Layer 3 device and downstream user hosts. The Layer 2 device then uses the message information to set up multicast forwarding entries to implement on-demand multicast data forwarding at the data link layer.

Configuring MLD Snooping Proxy: To conserve network bandwidth, you can configure MLD snooping proxy on the devices. Then the devices work as proxy devices between the upstream devices and downstream hosts and substitute for them to send MLD messages, maintain group memberships, and forward multicast messages based on the group member interface information. Before configuring MLD snooping proxy, familiarize yourself with the applicable environment, complete the pre-configuration tasks, and obtain the required data. This can help you complete the configuration task quickly and accurately.

Configuring IPv6 SSM Mapping: Some hosts can run only MLDv1. To enable such hosts to obtain the MLDv2 service, configure SSM mapping.

Setting the Maximum Number of Invalid IPv6 Layer 2 Multicast Protocol Packets That Can Be Stored: Set the maximum number of invalid IPv6 Layer 2 multicast protocol packets that can be stored. Then, you can effectively locate and rectify faults based on the information about the limited number of invalid messages.

Maintaining Static Layer 2 Multicast: The commands for maintaining Layer 2 multicast include those for clearing statistics about IGMP snooping and for debugging IGMP snooping.

Configuration Examples for Layer 2 Multicast: This section describes Layer 2 multicast configuration examples.