ZyXEL Communications SAM1316-22, User Manual

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SAM1316-22 User’s Guide
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IGMP
This chapter describes the IGMP screens.
18.1 IGMP
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1
sender to 1 recipient) or Broadcast (1 sender to everybody on the network).
Multicast delivers IP packets to just a group of hosts on the network.
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. See
RFC 1112 and RFC 2236 for information on IGMP versions 1 and 2, respectively.
18.2 IP Multicast Addresses
In IPv4, a multicast address allows a device to send packets to a specific group of
hosts (multicast group) in a different sub-network. A multicast IP address
represents a traffic receiving group, not individual receiving devices. IP addresses
in the Class D range (224.0.0.0 to 239.255.255.255) are used for IP multicasting.
Certain IP multicast numbers are reserved by IANA for special purposes (see the
IANA web site for more information).
18.2.1 IGMP Snooping
A layer-2 switch can passively snoop on IGMP Query, Report and Leave (IGMP
version 2) packets transferred between IP multicast routers/switches and IP
multicast hosts to learn the IP multicast group membership. It checks IGMP
packets passing through it, picks out the group registration information, and
configures multicasting accordingly. IGMP snooping allows the SAM1316-22 to
learn multicast groups without you having to manually configure them.
The SAM1316-22 forwards multicast traffic destined for multicast groups (that it
has learned from IGMP snooping or that you have manually configured) to ports