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Configuration Guide - IP Multicast

CloudEngine 8800, 7800, 6800, and 5800 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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Dropping Unknown Multicast Flows

Dropping Unknown Multicast Flows


Unknown multicast flows are multicast data flows that match no entry in the multicast forwarding table. By default, the switch broadcasts unknown multicast flows in the corresponding VLAN. Dropping unknown multicast flows reduces instant bandwidth usage compared with the broadcast mode.


  1. Run system-view

    The system view is displayed.

  2. Run vlan vlan-id

    The VLAN view is displayed.

  3. Run multicast drop-unknown

    The switch is configured to drop unknown multicast flows.


    If a VLANIF interface on a CE6870EI or CE6875EI switch has Layer 3 multicast enabled and is the inbound interface of multicast flows, do not use the multicast drop-unknown command in the corresponding VLAN. Otherwise, multicast flows may fail to be forwarded.

    After the multicast drop-unknown command is configured:
    • A CE6870EI or CE6875EI switch drops received unknown multicast data flows. As a result, multicast flows may not be forwarded.
    • Switches excluding the CE6870EI and CE6875EI drop the original unknown multicast data packets. Multicast data flows can be forwarded after the matching multicast forwarding entries are generated.
    • A switch drops protocol packets with reserved group addresses, such as Protocol Independent Multicast (PIM) Hello packets, Open Shortest Path First (OSPF) packets, and Bidirectional Forwarding Detection (BFD) packets. If no multicast function is enabled, the switch drops IGMP packets. If multicast functions are enabled, the switch processes IGMP packets normally.

  4. Run commit

    The configuration is committed.

Updated: 2019-04-20

Document ID: EDOC1100075361

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