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GS3700/XGS3700 Series User’s Guide

177

H A P T E R

2 2

Multicast

This chapter shows you how to configure various multicast features.

22.1 Multicast 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 Management Protocol) is a network-layer protocol used to establish
membership in an IPv4 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.

The Multicast Listener Discovery (MLD) protocol (defined in RFC 2710) is derived from IPv4's
Internet Group Management Protocol version 2 (IGMPv2). MLD uses ICMPv6 message types, rather
than IGMP message types. MLDv1 is similar to IGMPv2 and MLDv2 is similar to IGMPv3. MLD allows
an IPv6 switch or router to discover the presence of MLD listeners who wish to receive multicast
packets and the IP addresses of multicast groups the hosts want to join on its network.

MLD snooping and MLD proxy are analogous to IGMP snooping and IGMP proxy in IPv4. MLD
filtering controls which multicast groups a port can join.

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 website for more information).

In IPv6, multicast addresses provide the same functionality as IPv4 broadcast addresses.
Broadcasting is not supported in IPv6. A multicast address allows a host to send packets to all hosts
in a multicast group. Multicast scope allows you to determine the size of the multicast group. A
multicast address has a predefined prefix of ff00::/8.

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.