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Chapter 6 WAN
Multicast
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1 sender - 1 recipient) or
Broadcast (1 sender - everybody on the network). Multicast delivers IP packets to a group of hosts on
the network - not everybody and not just 1.
Figure 13 Multicast Example
In the multicast example above, systems A and D comprise one multicast group. In multicasting, the
server only needs to send one data stream and this is delivered to systems A and D.
IGMP (Internet Group Multicast Protocol) is a network-layer protocol used to establish membership in a
multicast group - it is not used to carry user data. The EMG2881-T20A supports both IGMP version 1
(IGMP-v1) and IGMP version 2 (IGMP-v2).
At start up, the EMG2881-T20A queries all directly connected networks to gather group membership.
After that, the EMG2881-T20A periodically updates this information. IP multicasting can be enabled/
disabled on the EMG2881-T20A WAN interface in the Web Configurator (WAN). Select None to disable IP
multicasting on these interfaces.
6.4 Management WAN
Use this screen to view, change, or add your EMG2881-T20A's Internet access settings. Click
Configuration > WAN > Management WAN. The following screen opens.
Figure 14 Configuration > WAN > Management WAN
EMG2881-T20A User's Guide
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