How does an S series switch enabled with Layer 2 multicast send Query messages when the network topology changes

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For an S series switch, when the ring network topology changes, Layer 2 multicast responds to two events by sending two Query messages with different source addresses.
- Responds to the link change event of the ring network.
Run the igmp-snooping send-query enable command to enable the switch to send IGMP Query messages in response to link change events. When receiving a link change event, the Layer 2 multicast module sends a Query message with source address 192.168.0.1 to all non-router ports. The source address can be changed using the igmp-snooping send-query source-address command.
- Responds to the event that the interface changes from the Blocked state to the Forwarding state.
Layer 2 multicast sends a Query message whose source address is 0. The message is sent to only the interface of which the status changes.

According to RFCs, Query messages whose source address is 0 cannot be used for querier election. Therefore, the Query message sent when the interface status changes will not affect querier election, but the Query message sent when the link changes may affect querier election. You can configure a static router interface to prevent Query messages from affecting querier election.

Other related questions:
How is convergence performance of Layer 2 multicast accelerated on an S series switch?
When the network topology changes, Layer 2 multicast detects the topology change by responding to notification messages of ring network protocols. Layer 2 multicast sends General Query messages in the VLAN where the topology changes to re-collect group member relationships. Ring network protocols include STP, MSTP, RRPP, Smart Link, and SEP. The ring network protocols supported by the switches excluding the S1700 are as follows: - STP: supported by all switch models - MSTP: supported by all switch models excluding the S2700SI - RRPP: supported by all switch models excluding the S1720 and S2700SI - Smart Link: supported by all switch models excluding the S1720, S2700SI, S2710SI, and S2700EI - SEP: supported by all switch models excluding the S1720, S2700SI, S2710SI, and S2700EI

How is an S series switch process the Query message with the destination MAC address as the unicast MAC address
After Layer 2 multicast is enabled on a switch, the switch checks the destination MAC addresses of received IGMP messages. If the destination MAC address of a packet does not match its destination IP address, the switch drops the packet. Therefore, when the switch receives IGMP Query messages with unicast destination MAC addresses, it drops the messages. As a result, user hosts cannot receive the Query messages, and multicast forwarding entries on the switch cannot be updated. Then multicast forwarding is interrupted. When the switch connects to an ME60 and the ME60 performs multicast replication on a per user basis, IGMP Query messages sent from the ME60 uses user MAC addresses as destination MAC addresses. The switch drops these IGMP Query messages. In this case, modify the configuration on the ME60 to ensure that the IGMP Query messages sent from the ME60 use destination MAC addresses mapping their destination IP addresses. Then the switch can generate a router port when receiving the Query messages and forward the Query message to user hosts.

Does an S series switch sends a Report message after receiving a Query message
If only IGMP snooping is enabled, an S series switch does not send Report messages after receiving Query messages. If IGMP snooping proxy or IGMP snooping Report suppression is also configured, the switch can construct and send Report messages according to existing entries after receiving Query messages.

Layer 2 multicast entries and usage of S series switches
For an S series switch, entries fall into protocol and forwarding entries. Protocol entries include router port entries and host port entries. You can run the display igmp-snooping router-port command to check router port entries, run the display igmp-snooping port-info command to check host port entries, and run the display l2-multicast forwarding-table command to check forwarding entries. Protocol entries are triggered by protocol packets or manually generated. They are used to identify the protocol exchange status. Forwarding entries are generated based on protocol entries and are used to guide subsequent multicast data forwarding.

How does an S series switch process packets when Layer 2 multicast references an ACL
In Layer 2 multicast, three functions need to reference the ACL. After an ACL is referenced, packets are processed based on ACL rules. If no rule is configured, packets are processed as follows: - IGMP snooping group policy: In V200R001 and earlier versions, the default rule is permit. In V200R002 and later versions, if default-permit is not configured, the default rule is deny; if default-permit is configured, the default rule is permit. - IGMP snooping prompt leave: In V200R001 and earlier versions, the default rule is permit. In V200R002 and later versions, if default-permit is not configured, the default rule is deny; if default-permit is configured, the default rule is permit. - IGMP snooping SSM policy: The default rule is deny.

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