GS1920 Series User’s Guide 161
CHAPTER 23
Multicast
23.1 Multicast Overview
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.
23.1.1 What You Can Do
•Use the Multicast Setup screen (Section 23.2 on page 163) to enable IGMP snooping to forward
group multicast traffic only to ports that are members of that group.
•Use the IPv4 Multicast Status screen (Section 23.3 on page 164) to view multicast group
information.
•Use the MVR screens (Section 23.5 on page 170) to create multicast VLANs and select the
receiver port(s) and a source port for each multicast VLAN.
23.1.2 What You Need to Know
Read on for concepts on Multicasting that can help you configure the screens in this chapter.
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).
IGMP Snooping
A 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.
