Multicast Forwarding
Configuring IGMP Snooping
Cisco 220 Series Smart Switches Administration Guide Release 1.1.0.x 169
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STEP 7 Click Apply. The IP Multicast group address is added, and the Running
Configuration is updated.
Configuring IGMP Snooping
To support selective Multicast forwarding (IPv4), IGMP Snooping must be enabled
globally and for each relevant VLAN.
By default, the switch forwards Multicast frames to all ports of the relevant VLAN,
essentially treating the frame as if it is a Broadcast. With IGMP Snooping, the
switch forwards Multicast frames to the ports that have registered Multicast
clients.
NOTE The switch supports IGMP Snooping on both static and dynamic VLANs.
When IGMP Snooping is enabled globally or on a VLAN, all IGMP packets are
forwarded to the CPU. The CPU analyzes the incoming packets, and determines
the following:
• Which ports are asking to join which Multicast groups on what VLAN.
• Which ports are connected to Multicast routers (Mrouters) that are
generating IGMP queries.
• Which ports are receiving PIM, OSFP, DVMRP, or IGMP query protocols.
Ports asking to join a specific Multicast group issue an IGMP report that specifies
which group the host wants to join. This results in the creation of a forwarding
entry in the Multicast forwarding database.
The IGMP Snooping Querier is used to support a Layer 2 Multicast domain of
snooping switches in the absence of a Multicast router. For example, where
Multicast content is provided by a local server, but the router (if one exists) on that
network does not support Multicast.
There should be only one IGMP querier in a Layer 2 multicast domain. The switch
supports standards-based IGMP querier election when more than one IGMP
querier is present in the domain.
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