Using the BayStack
IGMP Snooping
BayStack
Internet Group Management Protocol (IGMP), is used by IP Multicast routers to learn about the existence of host group members on their directly attached subnets (see RFC 2236). The IP Multicast routers get this information by broadcasting IGMP queries and listening for IP hosts reporting their host group memberships. This process is used to set up a client/server relationship between an IP Multicast source that provides the data streams and the clients that want to receive the data.
Figure 1-31 shows how IGMP is used to set up the path between the client and server. As shown in this example, the IGMP host provides an IP Multicast stream to designated routers which forward the IP Multicast stream on their local network only if there is a recipient.
The client/server path is set up as follows:
1.The designated router sends out a host membership query to the subnet and receives host membership reports from end stations on the subnet.
2.The designated routers then set up a path between the IP Multicast stream source and the end stations.
3.Periodically, the router continues to query end stations on whether to continue participation.
4.As long as any client continues to participate, all clients, including nonparticipating end stations on that subnet, receive the IP Multicast stream.
Note: Although the nonparticipating end stations can filter the IP Multicast traffic, the IP Multicast still exists on the subnet and consumes bandwidth.
