Multicast Filtering; Defining Igmp Snooping - Alcatel OmniStack LS 6248 User Manual

Multicast Filtering

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 or
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 the hosts
which subscribed to this service.
This section contains information for configuring Multicast forwarding and Multicast
TV, and includes the following sections:

• Defining IGMP Snooping

• Specifying Static Interfaces for a Multicast Group
• Displaying Interfaces Attached to a Multicast Router
• Configuring Multicast TV
• Defining Multicast TV Membership
Defining IGMP Snooping
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
or router to ensure that it will continue to receive the multicast service. This
procedure is called multicast filtering. The IGMP Snooping Querier is used to
support IGMP snooping where the multicast traffic is not routed.
The purpose of IP 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). The user can set the IGMP Querier mode to either V2 or
V3. (Default is V2). When working in IGMPv3 mode and detecting an IGMPv2
message, the switch will automatically change its mode to IGMPv2.
The IGMP Snooping Page contains parameters for configuring switches to forward
multicast traffic.
Command Attributes
Global Parameters
• IGMP Snooping Status — Indicates that the switch monitors network traffic to
determine which hosts want to receive multicast traffic.
• IGMP Snooping Version — Displays the IGMP Snooping version enabled on the
device.
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