Using the BayStack 350 10/100/1000 Series Switch
1-34
304376-B Rev 00
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.
IP Multicast can be optimized in a LAN by using IP Multicast filtering switches,
such as the BayStack 350 10/100/1000 Series Switches.
Note:
Although the non-participating endstations can filter the IP Multicast
traffic, the IP Multicast still exists on the subnet and consumes bandwidth.
kombk.book Page 34 Thursday, February 18, 1999 10:59 AM
