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Configuration Guide - IP Multicast

CloudEngine 12800 and 12800E V200R005C10

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, PIM (IPv4), PIM (IPv6), MSDP, multicast VPN, multicast route management (IPv4), multicast route management (IPv6), IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN, multicast network management.
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MLD Snooping SSM Mapping

MLD Snooping SSM Mapping

The source-specific multicast (SSM) model conserves multicast addresses and has higher security than the any-source multicast (ASM) model. Only MLDv2 supports SSM. A host running MLDv2 can specify multicast source addresses in Report messages. Some hosts can run only MLDv1. To enable these hosts to obtain the SSM service, multicast devices need to provide the SSM mapping function.

MLD snooping SSM mapping is a Layer 2 SSM mapping feature used on IPv6 multicast networks. With this feature configured, a Layer 2 device can convert (*, G) information in MLDv1 Report messages to (S, G) information based on static SSM mapping entries to provide the SSM service for MLDv1 hosts. Here, S stands for a multicast source, G stands for a group, and * stands for any multicast sources. The default SSM group address range is FF3x::/32, where x is not 1 or 2. You can configure an SSM group policy to change the SSM group address range.

In Figure 11-4, HostA runs MLDv2, whereas HostB runs MLDv1 and does not support MLDv2. To provide the SSM service to all hosts on the network, MLD snooping SSM mapping needs to be configured on the Layer 2 switch.

Figure 11-4 MLD snooping SSM mapping network diagram

Table 11-3 lists the mappings between multicast groups and multicast sources configured on the switch.

Table 11-3 SSM mapping entries

Multicast Group Address

Multicast Source Address





When the switch receives a Report message from HostB, it checks whether the group address in the message is in the SSM group address range.
  • If the group address is within the SSM group address range and matches an SSM mapping entry, the switch creates the following multicast forwarding entry to provide the SSM service for HostB.

    Group Address in MLDv1 Report Message

    Generated Multicast Forwarding Entry

    FF33::3 (from HostB)

    (FC00:0:0:3::3, FF33::3)

  • If the group address in the Report message is within the SSM group address range matches no SSM mapping entry matching, the switch does not provide the SSM service and drops the Report message.

  • If the group address in the Report message is out of the SSM group address range, the switch only provides the ASM service.

Updated: 2019-04-20

Document ID: EDOC1100074724

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