Using the BayStack 350 10/100/1000 Series Switch
IGMP Snooping
BayStack 350 switches can sense IGMP Host Membership Reports from attached stations and can use this information to set up a dedicated path between the requesting station and a local IP Multicast router. Once the pathway is established, the BayStack 350 switch blocks the IP Multicast stream from exiting any other port that does not connect to another Host Member, thus conserving bandwidth. The following describes how BayStack 350 switches provide the same benefit as IP Multicast routers, but in the local area:
IGMP (internet group management protocol) is a protocol (see RFC 2236) that is used by IP Multicast routers to learn the existence of host group members on their directly attached subnets. The IP Multicast routers learn about the existence of host groups by broadcasting IGMP queries and listening for IP hosts reporting their host group memberships. This process is useful for the client/server relationship that exists between an IP Multicast source that provides data streams to clients wanting to receive the data.
Figure 1-24 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 only forward the IP Multicast stream on their local network 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 non-participating endstations on that subnet, receive the IP Multicast stream.
Note: Although the
IP Multicast can be optimized in a LAN by using IP Multicast filtering switches, such as the BayStack 350 10/100/1000 Series Switches.
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