Dell PowerConnect 5548 User Guide - Page 509

Multicast Support Overview Multicast forwarding enables a single packet to be forwarded to multiple destinations. Layer 2 Multicast service is based on a Layer 2 device receiving a single packet addressed to a specific Multicast address. Multicast forwarding creates copies of the packet, and transmits the packets to the relevant ports. There are two types of Multicast groups: • Registered Multicast Group - When traffic addressed to a registered Multicast group is received, it is handled according to its entry in the Multicast Filtering Database and forwarded only to the registered ports. • Unregistered Multicast Group - If traffic addressed to an unregistered Multicast group is received, it is handled by a special entry in the Multicast Filtering Database. The default setting of this is to flood all such traffic (traffic in unregistered Multicast groups). The device supports: • Forwarding L2 Multicast Packets - Forwards Layer 2 Multicast packets. Layer 2 Multicast filtering is enabled by default, and is not user-configurable. • Filtering L2 Multicast Packets - Forwards Layer 2 packets to interfaces. If Multicast filtering is disabled, Multicast packets are flooded to all relevant ports. NOTE: The system supports Multicast filtering for 256 Multicast groups. Layer 2 Switching Layer 2 switching forwards Multicast packets to all relevant VLAN ports by default, managing the packet as a single Multicast transmission. While Multicast traffic forwarding is effective, it is not optimal, as irrelevant ports also receive the Multicast packets. The excess packets cause increased network traffic. Multicast forwarding filters enable forwarding of Layer 2 packets to a subset of ports instead of to all ports. Dell PowerConnect 55xx Systems User Guide 509