30 CHAPTER 3: USING MULTICAST FILTERING
A multicast packet is identified by the presence of a multicast group
address in the destination address field of the packet’s IP header.
Benefits of Multicast The benefits of using IP multicast are that it:
■ Enables the simultaneous delivery of information to many receivers in
the most efficient, logical way.
■ Reduces the load on the source (for example, a server) because it does
not have to produce multiple copies of the same data.
■ Makes efficient use of network bandwidth and scales well as the
number of participants or collaborators expands.
■ Works with other IP protocols and services, such as Quality of Service
(QoS).
There are situations where a multicast approach is more logical and
efficient than a unicast approach. Application examples include distance
learning, transmitting stock quotes to brokers, and collaborative
computing.
A typical use of multicasts is in video-conferencing, where high volumes
of traffic need to be sent to several endstations simultaneously, but where
broadcasting that traffic to all endstations would seriously reduce
network performance.
Multicast Filtering Multicast filtering is the process that ensures that endstations only receive
multicast traffic if they register to join specific multicast groups. With
multicast filtering, network devices only forward multicast traffic to the
ports that are connected to registered endstations.
Multicast filtering is used to restrict multicasts within a VLAN. It does not
route multicasts between different VLANs.
Figure 4
shows how a network behaves without multicast filtering and
with multicast filtering.
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