ZyXEL ES-3148 Guida Utente

ES-3148 User’s Guide

This chapter shows you how to configure various multicast features. 

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 Management 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, RFC 
2236 and RFC 3376 for information on IGMP versions 1, 2 and 3 respectively.

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). 

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.

The Switch can passively snoop on IGMP 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 Switch to learn multicast groups without 
you having to manually configure them.