Managing IPv4 and IPv6 Multicast 1153What Is Multicast Tunneling?If Multicast traffic is to be routed through a part of a network that does notsupport multicasting (routers which are not multicast capable) then themulticast packets are encapsulated in an IP datagram and sent as a unicastpacket. When the multicast router at the remote end of the tunnel receivesthe packet, the router strips off the IP encapsulation and forwards the packetas an IP Multicast packet. This process of encapsulating multicast packets inIP is called tunneling.What 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 PowerConnectM6220/M6348/M8024/M8024-k switch performs the multicast router role ofthe IGMP protocol, which means it collects the membership informationneeded by the active multicast routing protocol.The PowerConnect M6220/M6348/M8024/M8024-k switch supports IGMPVersion 3. Version 3 adds support for source filtering, which is the ability for asystem to report interest in receiving packets only from specific sourceaddresses, as required to support Source-Specific Multicast [SSM], or from allbut specific source addresses, sent to a particular multicast address. Version 3is designed to be interoperable with Versions 1 and 2.Understaning 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.
