Cisco 500 series Administration Manual page 266

Configuring Multicast Forwarding
Configuring IGMP Snooping
NOTE
STEP 1
STEP 2
Cisco 500 Series Stackable Managed Switch Administration Guide
By default, a Layer 2 switch forwards Multicast frames to all ports of the relevant
VLAN, essentially treating the frame as if it were a Broadcast. With IGMP Snooping
the switch forwards Multicast frames to ports that have registered Multicast
clients.
The switch supports IGMP Snooping only on static VLANs. It does not support
IGMP Snooping on 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, DVMRP, or IGMP query protocols.
These are displayed on the
Ports, asking to join a specific Multicast group, issue an IGMP report that specifies
which group(s) the host wants to join. This results in the creation of a forwarding
entry in the Multicast Forwarding Data Base.
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.
The speed of IGMP Querier activity must be aligned with the IGMP-snooping-
enabled switches. Queries must be sent at a rate that is aligned to the snooping
table aging time. If queries are sent at a rate lower than the aging time, the
subscriber cannot receive the Multicast packets. This is performed in the IGMP
Snooping Edit page.
To enable IGMP Snooping and identify the switch as an IGMP Snooping Querier on
a VLAN:
Click Multicast > IGMP Snooping. The
Enable or disable the IGMP Snooping status.
IGMP Snooping page.
IGMP Snooping
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