Multicast - ZyXEL Communications AMG1302-T11C User Manual

Chapter 8 Home Networking
Both RIP-2B and RIP-2M sends the routing data in RIP-2 format; the difference being that RIP-2B
uses subnet broadcasting while RIP-2M uses multicasting. Multicasting can reduce the load on
non-router machines since they generally do not listen to the RIP multicast address and so will not
receive the RIP packets. However, if one router uses multicasting, then all routers on your network
must use multicasting, also.

8.7.6 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.
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. IGMP version 2 (RFC 2236) is an
improvement over version 1 (RFC 1112) but IGMP version 1 is still in wide use. IGMP version 3
supports source filtering, reporting or ignoring traffic from specific source address to a particular
host on the network. If you would like to read more detailed information about interoperability
between IGMP version 2 and version 1, please see sections 4 and 5 of RFC 2236. The class D IP
address is used to identify host groups and can be in the range 224.0.0.0 to 239.255.255.255. The
address 224.0.0.0 is not assigned to any group and is used by IP multicast computers. The address
224.0.0.1 is used for query messages and is assigned to the permanent group of all IP hosts
(including gateways). All hosts must join the 224.0.0.1 group in order to participate in IGMP. The
address 224.0.0.2 is assigned to the multicast routers group.
At start up, the AMG1302-T11C queries all directly connected networks to gather group
membership. After that, the AMG1302-T11C periodically updates this information. IP multicasting
can be enabled/disabled on the AMG1302-T11C LAN and/or WAN interfaces in the web configurator
(LAN; WAN). Select None to disable IP multicasting on these interfaces.
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