Shiro ADSL 2/2+ Ethernet Modem - Manual (Page 45)

User Manual
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IGMP Proxy
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.
IGMP Proxy
Multicasting is a form of limited broadcast. UDP is used to send datagram’s 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 datagram’s 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.