Multicast Screens; Chapter 10 Multicast Screens; Igmp Introduction; Ip Multicast Addresses - ZyXEL Communications MSC1024G Series User Manual

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This chapter describes the Multicast screens.

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 RFCs 1112, 2236

and 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 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).

A layer-2 switch can passively snoop on IGMP Query, Report and Leave (IGMP versions 2

and 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 system to learn multicast groups without you having to manually configure them.

The system 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 system 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.

To allow better network performance, you can use IGMP proxy instead of a multicast routing

protocol in a simple tree network topology.

MSC1000G/1024G/1224G Series User's Guide

Multicast Screens

Msc1224g series Msc1000g series