Managing IPv4 and IPv6 Multicast 1171What Is IGMP?The Internet Group Management Protocol (IGMP) is used by IPv4 systems(hosts, L3 switches, and routers) to report their IP multicast groupmemberships to any neighboring multicast routers. The PowerConnect8000/8100-series switch performs the multicast router role of the IGMPprotocol, which means it collects the membership information needed by theactive multicast routing protocol.The PowerConnect 8000/8100-series switch also supports IGMP Version 3.Version 3 adds support for source filtering, which is the ability for a system toreport interest in receiving packets only from specific source addresses, asrequired to support Source-Specific Multicast [SSM], or from all but specificsource addresses, sent to a particular multicast address. Version 3 is designedto be interoperable with Versions 1 and 2.Understanding IGMP ProxyIGMP proxy enables a multicast router to learn multicast group membershipinformation and forward multicast packets based upon the groupmembership information. The IGMP Proxy is capable of functioning only incertain topologies that do not require Multicast Routing Protocols (i.e.,DVMRP, PIM-DM, and PIM-SM) and have a tree-like topology, as there is nosupport for features like reverse path forwarding (RPF) to correct packet routeloops.The proxy contains many downstream interfaces and a unique upstreaminterface explicitly configured. It performs the host side of the IGMP protocolon its upstream interface and the router side of the IGMP protocol on itsdownstream interfaces.The IGMP proxy offers a mechanism for multicast forwarding based only onIGMP membership information. The router must decide about forwardingpackets on each of its interfaces based on the IGMP membershipinformation. The proxy creates the forwarding entries based on themembership information and adds it to the multicast forwarding cache(MFC) in order not to make the forwarding decision for subsequent multicastpackets with same combination of source and group.
