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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 Proxy

MLD Snooping Proxy

Fundamentals

MLD snooping proxy enables a Layer 2 device to send Report messages to the upstream Layer 3 device in place of downstream hosts. This function reduces the number of MLD Report and Done messages received on the Layer 3 device. After MLD snooping proxy is configured on a Layer 2 device, the device functions as a host for the upstream device and a querier for the downstream hosts.

In Figure 11-5, the switch running MLD snooping directly forwards Query messages from the upstream router and Report/Done messages from downstream hosts. When there are many hosts on the network, redundant MLD messages increase the load of the router.

With MLD snooping proxy configured, the switch can terminate MLD Query messages sent from the router and MLD Done messages sent from hosts. When receiving these messages, the switch constructs new messages to send to the router or downstream hosts.

Figure 11-5 MLD snooping proxy network diagram

After MLD snooping proxy is configured on the Layer 2 device, the Layer 3 device considers that it interacts with only one user. The Layer 2 device interacts with the Layer 3 device and downstream hosts. The MLD snooping proxy function conserves bandwidth by reducing MLD message exchanges. The Layer 2 device functions as a querier to terminate a large number of protocol messages received from downstream hosts and maintain group memberships, reducing the load of the upstream Layer 3 device.

Implementation

A device that runs MLD snooping proxy creates and maintains a Layer 2 multicast forwarding table and sends multicast data to hosts based on the table. Table 11-4 describes how an MLD snooping proxy device processes MLD messages.

Table 11-4 MLD message processing on an MLD snooping proxy device

MLD Message Type

Processing Method

MLD General Query message

The device forwards the message to all ports in the local VLAN, excluding the port that has received the message. In addition, the device generates an MLD Report message based on the group memberships maintained locally and sends the message to all router ports.

MLD Last Listener Query or Multicast-Address-and-Source-Specific Query message

If the group specified in the message still has member ports in the matching multicast forwarding entry, the device responds with an MLD Report message to all router ports.

MLD Report message

  • If the multicast group specified in the message matches no forwarding entry, the device creates a forwarding entry, adds the message receiving port to the outbound interface list as a dynamic member port, starts the aging timer, and sends an MLD Report message of the group to all router ports.
  • If the multicast group matches a forwarding entry and the message receiving port is in the outbound interface list, the device resets the aging timer.
  • If the multicast group matches a forwarding entry but the port is not in the outbound interface list of the entry, the device adds the port to the list as a dynamic router port, and starts the aging timer.

MLD Done message

The device sends a Multicast-Address-Specific Query message to the port that has received the message. The device sends an MLD Done message to all router ports only when the last member port is deleted from the forwarding entry of the group.

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Updated: 2019-04-20

Document ID: EDOC1100074724

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