How does an S series switch elect an IGMP querier

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When a host subnet is connected to the interfaces on multiple devices, to avoid data conflict, only one interface is allowed to send Query messages. This interface is the querier. The other interfaces running IGMP can receive the IGMP messages in this subnet.
In IGMPv1, the querier is elected by a multicast routing protocol such as PIM. In IGMPv2 and IGMPv3, the switch interface with the lowest IP address acts as the querier.

Other related questions:
Does an S series switch enabled with IGMP snooping querier participate in IGMP querier election
After IGMP snooping querier is enabled on an S series switch, the switch periodically sends Query messages to users in a VLAN but does not participate in IGMP querier election or forward Query messages to a VLAN. Layer 2 multicast querier is used when the switch connects to no upstream Layer 3 device or when the IGMP querier function is not enabled on the upstream Layer 3 device. If an IGMP querier exists on the network, do not enable the IGMP snooping querier function on the switch. This is because this function affects querier election on the upstream Layer 3 device and causes multicast service failures.

How does IGMP elect a querier from multiple devices on a shared network segment
When a host network segment is connected to the interfaces on multiple devices, to avoid data conflict, only one device interface is allowed to send Query messages. This interface acts as the querier. The other device interfaces that run IGMP can receive to the IGMP messages on the network segment. In IGMPv1, querier selection depends on the multicast routing protocol, such as PIM. In IGMPv2 and IGMPv3, the device interface with the lowest IP address acts as the querier on the network segment.

How does an S series switch process IGMP messages of a later version
If the version of a received IGMP message is later than the IGMP snooping version configured on the switch, the switch processes the IGMP message as follows: - If the received message is a Report message, the switch forwards the message only to router ports and does not generate a member port or forwarding entry. - If the received message is a Query message, the switch broadcasts the message in the VLAN and sets the receiving port as a router port. After the multicast VLAN service is configured, IGMP messages are replicated and broadcast in user VLANs. If the switch receives many Group-Specific Query messages of a later version, the CPU usage may become high. If IGMP messages of a later version degrade service performance on the switch, change the IGMP snooping version to the later version.

IGMP snooping parameters of an S series switch
The following IGMP snooping parameters are provided: - Query-interval: specifies the interval for sending General Query messages. The system starts an aging timer for a member port when the port receives a Report message. The aging time is calculated using the following formula: Aging time = Robust variable x Query interval + Maximum response time for General Query messages On the S series modular switch, the default value is 60s. On S and E series fixed switches excluding the S1700, the default value is 125s. - Max-response-time: specifies the maximum response time for a Query message. After receiving a Query message, a device must send a response message within the specified time. The device may send the Report message at any time before the maximum response time expires. The default interval is 10s. - Robust-count: specifies the IGMP robustness variable. This parameter is set based on the link performance. If a link is unstable and many packets are discarded, increase the robustness variable. The default robustness variable is 2. - Last-member-query-interval: specifies the interval for sending Last Member Query messages. In IGMPv2 and IGMPv3, the system starts an aging timer for a member port when the port receives a Leave message. The aging time is calculated using the following formula: Aging time = Robust variable x Interval for sending Last Member Query messages The default interval is 1s. If the IGMP snooping querier is not configured, the parameter is used to calculate the aging time of member ports. - After a member port receives a Report message from the downstream host, the aging time is as follows: Aging time = Robust variable x Query interval + Maximum response time for General Query messages - After a member port receives a Leave message from the downstream host, the aging time is as follows: Aging time = Robust variable x Interval for sending Last Member Query messages Run the display igmp-snooping command to check parameter settings on an S series switch excluding the S1700.

How IGMP messages are transparently transmitted on an S series switch enabled with IGMP snooping
After global IGMP snooping is enabled on a switch, the switch sends all the IGMP messages received from a VLAN to the CPU for processing. If the multicast service is not configured in a VLAN and the switch needs to directly forward the IGMP messages of this VLAN without sending them to the CPU, run the protocol-transparent command in the VLAN view to enable transparent transmission of protocol packets. S series fixed switches support transparent transmission of protocol packets starting from V200R001, and only the S3700HI, S5710EI, S5720EI, S5700HI, S5710HI, S5720HI, S6700EI, andS6720EI support this function. S series modular switches support this function.

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