Usage Scenario
When a Layer 2 device receives an IGMP Membership Report message (Report or Leave message) from a group member, the Layer 2 device forwards the message to the directly connected Layer 3 device. A group member
host sends a Membership Report message in the following situations:
- When joining a multicast group, a host sends a Report message. When a multicast group has multiple members in a VLAN, the Layer 3 device receives duplicate Report messages from the member hosts.
- When receiving an IGMP General Query message, a host sends a Report message. Hosts use a timer to suppress duplicate Report messages on the same network segment. However, if the timer values on hosts are the same, the Layer 3 device can still receive
duplicate Report messages.
- A host running IGMPv2 or IGMPv3 sends a Leave message when leaving a multicast group. When a multicast group has multiple members in a VLAN, the Layer 3 device receives duplicate Leave messages from the member hosts.
After Report message suppression is enabled on a Layer 2 device, the device forwards only one IGMP Membership Report message to the upstream device in the following scenarios:
- When the first member joins a multicast group or a host sends a Report message in response to an IGMP Query message, the Layer 2 device forwards a Report message to the upstream device. The upstream device can create or maintain the matching forwarding
entry based on the Report message.
- When the last member of a multicast group leaves the group, the Layer 2 device forwards a Leave message to the upstream device. The upstream device then deletes the matching forwarding entry.
This reduces the number of IGMP messages on the network.
Prerequisites
IGMP snooping has been enabled globally using the igmp-snooping enable (system view) command.
Configuration Impact
The configuration takes effect only after you run the igmp-snooping enable (VLAN view) command to enable IGMP snooping
in the VLAN.
When receiving a Leave message from a group member, the device sends Group-Specific Query messages to check whether the group has other members on the network segment.
IGMP message suppression cannot be configured in a VLAN if the corresponding VLANIF interface has Layer 3 multicast function (such as IGMP and PIM) enabled.
The functions of IGMP snooping proxy and IGMP message suppression cannot be configured in the same VLAN.
If multicast VLAN replication is configured on the switch, the IGMP message suppression function cannot be enabled in user VLANs.
- The device can suppress duplicate Report messages even when IGMP message suppression is disabled. The default suppression time is 10 seconds. To change the suppression time, run the igmp-snooping suppress-time suppress-time command. If the suppress-time is set to 0, all the membership packets are forwarded immediately.
- This function cannot suppress IGMPv3 packets.