Cisco 220 Series Smart Plus Administration Manual page 161

Multicast Forwarding
Multicast Forwarding
Cisco 220 Series Smart Plus Switches Administration Guide Release 1.0.0.x
The switch maintains lists of Multicast groups for each VLAN, and this manages
the Multicast information that each port should receive. The Multicast groups and
their receiving ports can be configured statically or learned dynamically using
IGMP or Multicast Listener Discovery (MLD) protocols snooping.
Multicast registration is the process of listening and responding to Multicast
registration protocols. The available protocols are IGMP for IPv4 and MLD for IPv6.
When IGMP/MLD snooping is enabled in a device on a VLAN, it analyzes the IGMP/
MLD packets it receives from the VLAN connected to the device and Multicast
routers in the network.
When a device learns that a host is using IGMP/MLD messages to register to
receive a Multicast stream, optionally from a specific source, the device adds the
registration to its Multicast Forwarding Data Base (MFDB).
IGMP/MLD snooping can effectively reduce Multicast traffic from streaming
bandwidth-intensive IP applications. A device using IGMP/MLD snooping only
forwards Multicast traffic to the hosts interested in that traffic. This reduction of
Multicast traffic reduces the packet processing at the device, and also reduces
the workload of the end hosts, since they do not have to receive and filter all of the
Multicast traffic generated in the network.
The following versions are supported:
• IGMP v1/v2/ v3
• MLD v1/v2
• A simple IGMP Snooping Querier
An IGMP Querier is required to facilitate the IGMP protocol on a given subnet. In
general, a Multicast router is also an IGMP Querier. When there are multiple IGMP
Queriers in a subnet, the queriers elect a single querier as the primary querier.
The switch can be configured to be an IGMP Querier as a backup querier, or in
situation where a regular IGMP Querier does not exist. The switch is not a full
capability IGMP Querier.
If the switch is enabled as an IGMP Querier, it starts after 1/4 query interval have
passed with no IGMP traffic (queries) detected from a Multicast router. In the
presence of other IGMP Queriers, the device might (or might not) stop sending
queries, based on the results of the standard querier selection process.
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