ZyXEL Communications VES1724-56, Руководство пользователя

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VES1724-56 User’s Guide
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Multicast
This chapter shows you how to configure various multicast features.
24.1 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 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.
24.1.1 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).
24.1.2 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.
24.1.3 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.
The Switch 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. IGMP
snooping generates no additional network traffic, allowing you to significantly reduce multicast
traffic passing through your Switch.