ZyXEL Communications ZyXEL Dimension ES-3124 - Manual (Page 167)

Dimension ES-3124 Ethernet Switch
Multicast 22-1
This chapter shows you how to configure various multicast features.
22.1 Overview
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. Refer to RFC 1112 and RFC 2236 for information on IGMP versions 1 and
2 respectively.
22.1.1 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 subnetwork. 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).
22.1.2 IGMP Filtering
With the IGMP filtering feature, you can control which IGMP groups a subscriber on a port can join. This allows
you to control the distribution of multicast services (such as content information distribution) based on service
plans and types of subscription.
You can set the switch to filter the multicast group join reports on a per-port basis by configuring an IGMP filtering
profile and associating the profile to a port.
22.1.3 IGMP Snooping
IGMP (Internet Group Multicast Protocol) is a session-layer protocol used to establish membership in a multicast
group - it is not used to carry user data. Refer to RFC 1112 and RFC 2236 for information on IGMP versions 1 and
2 respectively.
A 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
Chapter 22
Multicast