BayStack 450 10/100/1000 Series Switches
309978-D Rev 01 1-69
IGMP Snooping
BayStack 450 switches can sense Internet Group Management Protocol (IGMP)
host membership reports from attached stations. The switches use this information
to set up a dedicated path between the requesting station and a local IP multicast
router. After the pathway is established, the BayStack 450 switch blocks the IP
multicast stream from exiting any other port that does not connect to another host
member, thus conserving bandwidth. The following discussion describes how
BayStack 450 switches provide the same benefit as IP multicast routers, but in the
local area.
IP multicast routers use IGMP 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 1-40 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 that 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.
IP multicast can be optimized in a LAN by using IP multicast filtering switches,
such as the BayStack 450 switch.
Note: Although the nonparticipating end stations can filter the IP multicast
traffic, the IP multicast still exists on the subnet and consumes bandwidth.
To Next Page
Loading...
Need help?
General