What Is A Multicast; What Is Multicast Filtering - 3Com SuperStack II Manual

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HAPTER ULTICAST
What is a
Multicast?
What is Multicast
Filtering?
F
ILTERING
A multicast is a packet that is sent to a subset of endstations in a LAN, or
VLAN, that belong to a multicast group. If the network is set up correctly,
a multicast can only be sent to an endstation if it has joined the relevant
group.
A typical use of multicasts is 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.
Multicasts are similar to broadcasts — by default, they are sent to all
endstations on a LAN or VLAN. Multicast filtering is the system by which
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.
Figure 44 The effect of multicast filtering