Dell PowerConnect 55xx Systems User Guide 509Multicast Support OverviewMulticast forwarding enables a single packet to be forwarded to multipledestinations. Layer 2 Multicast service is based on a Layer 2 device receiving asingle packet addressed to a specific Multicast address. Multicast forwardingcreates 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 registeredMulticast group is received, it is handled according to its entry in theMulticast Filtering Database and forwarded only to the registeredports.• Unregistered Multicast Group — If traffic addressed to anunregistered Multicast group is received, it is handled by a specialentry in the Multicast Filtering Database. The default setting of this isto flood all such traffic (traffic in unregistered Multicast groups).The device supports:• Forwarding L2 Multicast Packets — Forwards Layer 2 Multicastpackets. Layer 2 Multicast filtering is enabled by default, and is notuser-configurable.• Filtering L2 Multicast Packets — Forwards Layer 2 packets tointerfaces. If Multicast filtering is disabled, Multicast packets areflooded to all relevant ports.NOTE: The system supports Multicast filtering for 256 Multicast groups.Layer 2 SwitchingLayer 2 switching forwards Multicast packets to all relevant VLAN ports bydefault, managing the packet as a single Multicast transmission. WhileMulticast traffic forwarding is effective, it is not optimal, as irrelevant portsalso receive the Multicast packets. The excess packets cause increasednetwork traffic. Multicast forwarding filters enable forwarding of Layer 2packets to a subset of ports instead of to all ports.
