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Configuration Guide - IP Multicast

S7700 and S9700 V200R013C00

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, IPv4 PIM, IPv6 PIM, MSDP, multicast VPN, layer 3 multicast CAC, IPv4 multicast route management, IPv6 multicast route management, IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN replication, layer 2 multicast CAC, multicast network management.
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Discarding Unknown Multicast Flows

Discarding Unknown Multicast Flows


Unknown multicast flows are those that do not match any entry in the multicast forwarding table or match multicast forwarding entries with an empty outbound interface list. These flows are not requested by users. The default method that a switch uses to process unknown IPv6 multicast flows depends on whether Layer 2 multicast is enabled and which Layer 2 multicast forwarding mode is used:
  • If Layer 2 multicast is not enabled on the switch, the switch broadcasts unknown multicast flows in the corresponding VLAN.

  • If Layer 2 multicast is enabled, the switch broadcasts unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drops unknown multicast flows in IP address-based forwarding mode.

If a switch broadcasts unknown multicast flows in a VLAN, you can configure the switch to drop unknown multicast flows, reducing instant bandwidth usage.


  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 discard unknown multicast flows.


    The multicast drop-unknown command configures the switch to discard all unknown IPv4 and IPv6 multicast packets, including the protocol packets that are transparently transmitted within the VLAN and use the reserved multicast address.

Updated: 2019-04-08

Document ID: EDOC1100065742

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