Multicast
Multicast Forwarding Overview
262 Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
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Typical Multicast Setup
While Multicast routers route Multicast packets between IP subnets, Multicast-capable
Layer 2 switches forward Multicast packets to registered nodes within a LAN or VLAN.
A typical setup involves a router that forwards the Multicast streams between private and/or
public IP networks, a device with IGMP/MLD snooping capabilities, and a Multicast client
that wants to receive a Multicast stream. In this setup, the router sends IGMP/MLD queries
periodically.
Multicast Operation
In a Layer 2 Multicast service, a Layer 2 switch receives a single frame addressed to a specific
Multicast address. It creates copies of the frame to be transmitted on each relevant port.
When the device is IGMP/MLD-snooping-enabled and receives a frame for a Multicast
stream, it forwards the Multicast frame to all the ports that have registered to receive the
Multicast stream using IGMP/MLD Join messages.
The system maintains lists of Multicast groups for each VLAN, and these lists manage 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 MLD protocols
snooping.
Multicast Registration (IGMP/MLD 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, the device 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 the
MFDB.
The following versions are supported:
• IGMP v1/v2/ v3
• MLD v1/v2
NOTE The device supports IGMP/MLD Snooping only on static VLANs. It does not support IGMP/
MLD Snooping on dynamic VLANs.
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