TP-Link 10GE T1700G-28TQUN V1 User Guide - Page 122
IGMP Messages, IGMP Snooping Fundamentals, Router Port, Member Port
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IGMP Messages The switch, running IGMP snooping, processes the IGMP messages of different types as follows. 1. IGMP Query Message IGMP query message, sent by the router, falls into two types, IGMP general query message and IGMP group-specific-query message. The router regularly sends IGMP general message to query if the multicast groups contain any member. When receiving IGMP leave message, the receiving port of the router will send IGMP group-specific-query message to the multicast group and the switch will forward IGMP group-specific-query message to check if other members in the multicast group of the port need this multicast. When receiving IGMP general query message, the switch will forward them to all other ports in the VLAN owning the receiving port. The receiving port will be processed: if the receiving port is not a router port yet, it will be added to the router port list with its router port time specified; if the receiving port is already a router port, its router port time will be directly reset. When receiving IGMP group-specific-query message, the switch will send the group-specific query message to the members of the multicast group being queried. 2. IGMP Report Message IGMP report message is sent by the host when it applies for joining a multicast group or responses to the IGMP query message from the router. When receiving IGMP report message, the switch will send the report message via the router port in the VLAN as well as analyze the message to get the address of the multicast group the host applies for joining. The receiving port will be processed: if the receiving port is a new member port, it will be added to the multicast address table with its member port time specified; if the receiving port is already a member port, its member port time will be directly reset. 3. Member Leave Message The host will send IGMP leave message when leaving a multicast group to inform the router of its leaving. When Immediate Leave is not enabled in a VLAN and a leave message is received on a port of this VLAN, the switch will generate Multicast-Address-Specific Queries (MASQs) on this port to check if there are other members in this multicast group. The user can control when a port membership is removed for an existing address in terms of the number and interval of MASQs. If there is no Report message received from this port during the switch maximum response time, the port on which the MASQ was sent is deleted from the multicast group. If the deleted port is the last member of the multicast group, the multicast group is also deleted. The switch will send leave message to the router ports of the VLAN. In IPv4,Layer 2 switches can use IGMP snooping to limit the flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that IPv4 multicast data is selectively forwarded to a list of ports that want to receive the data. This list is constructed by snooping IPv4 multicast control packets. IGMP Snooping Fundamentals 1. Ports Router Port: Indicates the switch port directly connected to the multicast router. Member Port: Indicates a switch port connected to a multicast group member. 112