SMC Networks 7500A/VCP - annexe 1 Management Manual - Multicast Configuration

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Multicast Configuration

Multicasting is used to support real-time applications such as video 

conferencing or streaming audio. A multicast server does not have to 

establish a separate connection with each client. It merely broadcasts its 

service to the network, and any hosts that want to receive the multicast 

register with their local multicast switch/router. Although this approach 

reduces the network overhead required by a multicast server, the broadcast 

traffic must be carefully pruned at every multicast switch/router it passes 

through to ensure that traffic is only passed on to hosts that subscribed to 

this service.

This switch uses IGMP (Internet Group Management Protocol) to query 

for any attached hosts that want to receive a specific multicast service. It 

identifies the ports containing hosts requesting to join the service and 

sends data out to those ports only. It then propagates the service request 

up to any neighboring multicast switch/router to ensure that it will 

continue to receive the multicast service. This procedure is called multicast 

filtering.

The purpose of multicast filtering is to optimize a switched network’s 

performance, so multicast packets will only be forwarded to those ports 

containing multicast group hosts or multicast routers/switches, instead of 

flooding traffic to all ports in the subnet (VLAN.)

Configuring IGMP Parameters

You can configure the switch to forward multicast traffic intelligently. 

Based on the IGMP query and report messages, the switch forwards traffic 

only to the ports that request multicast traffic. This prevents the switch 

from broadcasting the traffic to all ports and possibly disrupting network 

performance.