Cisco SR224T Administration Guide - Page 191
Typical Multicast Setup, Multicast Operation, Protocol IGMP snooping capabilities
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Configuring Multicast Forwarding Multicast Forwarding 15 For Multicast forwarding to work across IP subnets, nodes, and routers must be Multicast-capable. A Multicast-capable node must be able to: • Send and receive Multicast packets. • Register the Multicast addresses being listened to by the node with local routers, so that local and remote routers can route the Multicast packet to the nodes. Typical Multicast Setup While Multicast routers route Multicast packets between IP subnets, Multicastcapable Layer 2 switches forward Multicast packets to registered nodes within a LAN or VLAN. A typical setup involves a router that forwards the Multicast streams between private and/or public IP networks, a switch with Internet Group Membership Protocol (IGMP) snooping capabilities, or Multicast Listener Discovery (MLD) snooping, and a Multicast client that wants to receive a Multicast stream. In this setup, the router sends IGMP queries periodically. NOTE MLD for IPv6 is derived from the IGMP v2 for IPv4. Even though the description in this section is mostly for IGMP, it also describes coverage of MLD where implied. These queries reach the switch, which in turn floods the queries to the VLAN, and also learns the port where there is a Multicast router (Mrouter). When a host receives the IGMP query message, it responds with an IGMP Join message saying that the host wants to receive a specific Multicast stream and optionally from a specific source. The switch with the IGMP snooping analyzes the Join messages, and learns that the Multicast stream the host has requested must be forwarded to this specific port. It then forwards the IGMP Join to the Mrouter only. Similarly, when the Mrouter receives an IGMP Join message, it learns the interface from which it received the Join messages that wants to receive a specific Multicast stream. The Mrouter forwards the requested Multicast stream to the interface. Multicast Operation In a Layer 2 Multicast service, a Layer 2 switch receives a single frame addressed to a specific Multicast address. It creates copies of the frame to be transmitted on each relevant port. When the switch is IGMP/MLD-snooping-enabled and receives a frame for a Multicast stream, it forwards the Multicast frame to all the ports that have registered to receive the Multicast stream using IGMP Join messages. Cisco Small Business 200 Series Smart Switch Administration Guide 192