D-Link DGS-3620-28TC-SI Product Manual - Page 212
IGMP Version 3, Specific Group Membership Query if Group Address is Present
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xStack® DGS-3620 Series Managed Switch Web UI Reference Guide The IGMP Type codes are shown below: Type Meaning 0x11 Membership Query (if Group Address is 0.0.0.0) 0x11 Specific Group Membership Query (if Group Address is Present) 0x16 Membership Report (version 2) 0x17 Leave a Group (version 2) 0x12 Membership Report (version 1) Table 5-1 IGMP Type Codes IGMP packets enable multicast routers to keep track of the membership of multicast groups, on their respective subnetworks. The following outlines what is communicated between a multicast router and a multicast group member using IGMP. A host sends an IGMP "report" to join a group A host will never send a report when it wants to leave a group (for version 1). A host will send a "leave" report when it wants to leave a group (for version 2). Multicast routers send IGMP queries (to the all-hosts group address: 224.0.0.1) periodically to see whether any group members exist on their subnetworks. If there is no response from a particular group, the router assumes that there are no group members on the network. The Time-to-Live (TTL) field of query messages is set to 1 so that the queries will not be forwarded to other subnetworks. IGMP version 2 introduces some enhancements such as a method to elect a multicast querier for each LAN, an explicit leave message, and query messages that are specific to a given group. The states a computer will go through to join or to leave a multicast group are shown below: Figure 5-66 IGMP State Transitions IGMP Version 3 The current release of the Switch now implements IGMPv3. Improvements of IGMPv3 over version 2 include: • The introduction of the SSM or Source Specific Multicast. In previous versions of IGMP, the host would receive all packets sent to the multicast group. Now, a host will receive packets only from a specific source or sources. This is done through the implementation of include and exclude filters used to accept or deny traffic from these specific sources. 202