Multicast packets can be forwarded normally when IGMP snooping is not configured. However, users cannot receive multicast packets after IGMP snooping is configured.
If so, the switch only forwards IGMP Report messages to router ports and does not generate group member ports and forwarding entries.
Run the display igmp-snooping configuration command to check the IGMP snooping configuration. If the IGMP snooping version configured on the switch is earlier than that running on user hosts, run the igmp-snooping version version command to set the IGMP snooping version to be the same as the IGMP version running on user hosts.
Multicast addresses ranging from 232.0.0.0 to 232.255.255.255 are SSM group addresses by default. After IGMP snooping is configured, multicast entries cannot be generated for multicast data from the 232.X.X.X network segment by default. Therefore, users cannot receive multicast data after IGMP snooping is configured. When this problem occurs, you need to check the version of the IGMP messages sent by user hosts, and change the configuration on the switch based on the IGMP version. If no IGMP querier is configured on the entire Layer 2 network, you are advised to run the igmp-snooping querier enable command on the switch closest to the multicast source to configure the Layer 2 multicast querier function.
# acl number 2100 //ACL 2100 indicates the user-defined multicast group address range. You are advised to use an empty ACL rule. # vlan 100 igmp-snooping enable igmp-snooping ssm-policy 2100 //Specify a new SSM group address range. An empty ACL rule indicates that Layer 2 multicast considers all multicast group addresses as non-SSM group addresses, so forwarding entries can be generated for multicast data from the 232.X.X.X network segment. #
# acl number 2100 # vlan 100 igmp-snooping enable igmp-snooping version 3 //Set the version of the IGMP messages that can be processed by IGMP snooping to IGMPv3. igmp-snooping ssm-policy 2100 #
# vlan 100 igmp-snooping enable igmp-snooping version 3 //Set the version of the IGMP messages that can be processed by IGMP snooping to IGMPv3. #
If the general query interval on the switch is smaller than the general query interval on the upstream IGMP querier or IGMP snooping device, the switch may incorrectly age out some IGMP snooping entries that are still in use. As a result, multicast packets matching these entries cannot be forwarded.
Run the display igmp-snooping command to check IGMP snooping parameters. If the general query interval on the switch is smaller than the general query interval on the upstream IGMP querier or IGMP snooping device, run the igmp-snooping query-interval query-interval command to increase the IGMP snooping general query interval. It is recommended that the upstream and downstream devices use the same general query interval.
On Huawei fixed switches, the default IGMP general query interval is 60 seconds, and the default IGMP snooping general query interval is 125 seconds.
The switch does not listen to IGMP Query messages in a VLAN after router port dynamic learning is disabled in the VLAN.
Run the display igmp-snooping configuration command to check whether router port dynamic learning is disabled. If the command output contains "undo igmp-snooping router-learning", run the igmp-snooping router-learning command to enable dynamic learning of router ports in the VLAN.
Configure fast leave in a VLAN only when each interface in the VLAN connects to only one host. If a member port is connected to multiple hosts and fast leave is enabled in the VLAN, the switch immediately deletes the forwarding entry of the member port after receiving an IGMP Leave message from the member port, and does not send a Group-Specific Query message. Therefore, multicast packets cannot be forwarded.
Run the display igmp-snooping configuration command to check whether fast leave is enabled. If the command output contains "igmp-snooping prompt-leave", run the undo igmp-snooping prompt-leave command in the VLAN view to disable fast leave.
If the Router-Alert option is configured, the switch checks the Option field of IGMP messages and discards messages without the Router-Alert option.
Run the display igmp-snooping configuration command to check whether the Router-Alert option is configured. If the command output contains "igmp-snooping require-router-alert", run the undo igmp-snooping require-router-alert command in the VLAN view to delete the configuration.
The multicast group policy limits the multicast groups that hosts in a VLAN can join. Run the display igmp-snooping configuration command to verify the multicast group policy configuration. If an access control list (ACL) is configured, run the display acl command to verify the ACL configuration.
If Layer 2 multicast filtering is configured on an interface, the interface discards the UDP packets from the specified VLAN.
Run the undo multicast-source-deny command in the physical interface view to disable Layer 2 multicast filtering.
In the Layer 2 multicast scenario, if the corresponding VLANIF interface is created and the Layer 3 multicast function is configured on the VLANIF interface, the switch forwards multicast data in the same way as when both Layer 2 and Layer 3 multicast services are enabled. That is, Layer 2 multicast maintains the physical outbound interface for Layer 3 multicast, enabling accurate forwarding of multicast data.
In this scenario, if the protocol status of the VLANIF interface is Down, multicast traffic cannot be forwarded. In this case, you are advised to delete the Layer 3 multicast configuration on the VLANIF interface and use the Layer 2 multicast forwarding mechanism to forward multicast traffic.
In the Layer 2 multicast scenario, if the corresponding VLANIF interface is created and bound to a VPN instance, Layer 2 multicast does not take effect and traffic is broadcast. In this case, if the VLAN transmits only Layer 2 services, you are advised to delete the VPN instance bound to the corresponding VLANIF interface. If both Layer 2 and Layer 3 multicast services of a VPN are transmitted in the VLAN, it is recommended that you configure both PIM and IGMP on the VLANIF interface.