Operation Manual – MulticastH3C S5500-EI Series Ethernet Switches Chapter 2 IGMP Snooping Configuration2-6forwards it through all its router ports in the VLAN and all member ports for thatmulticast group, and performs the following:z If any IGMP report in response to the group-specific query is heard on a memberport before its aging timer expires, this means that some host attached to the portis receiving or expecting to receive multicast data for that multicast group. Theswitch resets the aging timer of the member port.z If no IGMP report in response to the group-specific query is heard on a memberport before its aging timer expires, this means that no hosts attached to the portare still listening to that group address: the switch removes the port from theoutgoing port list of the forwarding table entry for that multicast group when theaging timer expires.2.1.4 Processing of Multicast Protocol MessagesWith Layer 3 multicast routing enabled, an IGMP Snooping switch processes multicastprotocol messages differently under different conditions, specifically as follows:1) If only IGMP is enabled, or both IGMP and PIM are enabled on the switch, theswitch handles multicast protocol messages in the normal way.2) In only PIM is enabled on the switch:z The switch broadcasts IGMP messages as unknown messages in the VLAN.z Upon receiving a PIM hello message, the switch will maintain the correspondingrouter port.3) When IGMP is disabled on the switch, or when IGMP forwarding entries arecleared (by using the reset igmp group command):z If PIM is disabled, the switch clears all its Layer 2 multicast entries and routerports.z If PIM is enabled, the switch clears only its Layer 2 multicast entries withoutdeleting its router ports.4) When PIM is disabled on the switch:z If IGMP is disabled, the switch clears all its router ports.z If IGMP is enabled, the switch maintains all its Layer 2 multicast entries and routerports.2.1.5 Protocols and StandardsIGMP Snooping is documented in:z RFC 4541: Considerations for Internet Group Management Protocol (IGMP) andMulticast Listener Discovery (MLD) Snooping Switches
