Zyxel VES-1616FE-55A [139/318] Ip multicast addresses

Zyxel VES-1616FE-55A [139/318] Ip multicast addresses
VES-1616FE-55A User’s Guide
139
CHAPTER 18
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, RFC 2236,
and RFC 3376 for information on IGMP versions 1, 2, and 3, 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 or
3) 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 VES-1616FE-55A to learn multicast groups without you having to manually
configure them.
The VES-1616FE-55A forwards multicast traffic destined for multicast groups (that it has
learned from IGMP snooping or that you have manually configured) to ports that are members
of that group. The VES-1616FE-55A discards multicast traffic destined for multicast groups
that it does not know. IGMP snooping generates no additional network traffic, allowing you to
significantly reduce multicast traffic passing through your device.

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