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When Users Connected to an S7700 Configured with Layer 3 Multicast Frequently Switch Channels, Frame Freezing Occurs

Publication Date:  2019-03-26 Views:  113 Downloads:  0

Issue Description

Software version: V200R008

Problem description: An S7700 is configured with Layer 3 multicast and functions as the gateway for receivers. Users report that when they frequently switch channels on receivers, frame freezing occurs.

Handling Process

When a user switches channels, the user leaves the original multicast group and joins a new multicast group. It is suspected that old entries are not deleted. Therefore, check IGMP entries.

<HUAWEI> display igmp group interface vlanif100

Interface group report information of VPN instance: public net


  Total 1 IGMP Group reported

   Group Address   Last Reporter   Uptime      Expires         00:01:38    00:00:32         00:01:18    00:01:07         00:00:52    00:01:18         00:00:48    00:01:22         00:00:45    00:02:07   

It is found that there are a large number of residual IGMP and PIM entries. These entries are not deleted when users switch channels. Therefore, the switch forwards all multicast traffic matching these entries to the receiver. As a result, the traffic rate exceeds the bandwidth or processing capability of the interface on the receiver, causing frame freezing.

Root Cause

By default, after receiving a Leave message from a multicast group member, the switch sends a Group-Specific Query message. If no IGMP Report message is received from the multicast group member within 2 seconds (default value, which can be manually adjusted), the switch deletes the IGMP and PIM entries. If a user switches channels too fast, for example, switching multiple channels within 2 seconds, a large number of entries will not be deleted.


If the switch is directly connected to terminals, configure the IGMP fast leave function on the switch. This function enables an IGMP querier to delete IGMP entries immediately after receiving Leave messages from multicast group members, without sending Group-Specific Query messages.

[HUAWEI] interface vlanif 100

[HUAWEI-Vlanif100] igmp prompt-leave

If the switch is connected to other switches (in this case, an interface of the switch is connected to multiple terminals), configuring IGMP fast leave on a VLANIF interface will make all multicast group members disconnected once a member in the same group leaves the multicast group. Therefore, configure the fast leave function in a VLAN on the switch that is directly connected to terminals.

Perform the following operations in different scenarios:

  • If a Layer 2 switch is directly connected to terminals, configure fast leave on its interfaces connected to terminals.

1. Run the system-view command to enter the system view.

2. Run the vlan vlan-id command to enter the VLAN view.

3. Run the igmp-snooping prompt-leave [ group-policy acl-number [ default-permit ] ] command to enable the fast leave function.

  • If a Layer 2 switch is connected to an access switch that is not managed by the NMS or does not have Layer 2 multicast configured, configure host-based fast leave on the Layer 2 switch.

1. Run the system-view command to enter the system view.

2. Run the vlan vlan-id command to enter the VLAN view.

3. Run the igmp-snooping host-based prompt-leave command to configure host-based fast leave.


If users frequently leave and join multicast groups, you can configure the IGMP fast leave function using an appropriate command based on the specific scenario.