518 Dell PowerConnect 55xx Systems User Guide
FILE LOCATION: C:\Users\gina\Desktop\Checkout_new\Maintenance Projects\Dell
Contax\CxUGSwitching_Multicast.fm
DELL CONFIDENTIAL – PRELIMINARY 9/11/12 - FOR PROOF ONLY
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.
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