User guide

ADSL2+ Ethernet USB Combo Router - User Guide
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4.5.10 IGMP Proxy
Multicasting is a form of limited broadcast. UDP is used to send datagrams to all hosts that
belong to what is called a Host Group. A host group is a set of one or more hosts identified by a
single IP destination address. The following statements apply to host groups:
• Anyone can join or leave a host group at will.
• There are no restrictions on a host’s location.
• There are no restrictions on the number of members that may belong to a host group.
• A host may belong to multiple host groups.
• Non-group members may send UDP datagrams to the host group.
Multicasting is useful when the same data needs to be sent to more than one device. For instance,
if one device is responsible for acquiring data that many other devices need, then multicasting is
a natural fit. Note that using multicasting as opposed to sending the same data to individual
devices uses less network bandwidth. The multicast feature also enables you to receive multicast
video streams from multicast servers.
IP hosts use Internet group management protocol (IGMP) to report their multicast group
memberships to neighboring routers. Similarly, multicast routers use IGMP to discover which of
their hosts belong to multicast groups. Your router supports IGMP proxy that handles IGMP
messages. When enabled, your router acts as a proxy for a LAN host making requests to join and
leave multicast groups, or a multicast router sending multicast packets to multicast groups on the
WAN side.
Figure 1-21 : IGMP Proxy