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DES-7200 Configuration Guide Chapter 1 IPv4 Multicast
Configuration
1-1
1 IPv4 Multicast
Configuration
1.1 Overview
This chapter introduces how to configure the IPv4 multicast routing protocol. For
the configuration commands of the multicast routing, please refter to the chapter
of Multicast Routing Configuration Commands.
The traditional IP transmission only allows the unicast or broadcast
communication. But the multicast technology allows one host to send the packets
to some other hosts, which are called the group members.
Send the packets to the group member destined to the Class-D network address
(224.0.0.0~239.255.255.255). Multicast packets are UDP packets with best effort
service. It does not provide reliable transmission and error control as TCP.
The multicast environment consists of senders and receivers. The sender sends
multicast packets with a multicast group address used to distinguish different
multicast flows. However, only the members of a group can receive the message
destined to this group.
Membership in a multicast group is dynamic; hosts can join and leave at any time.
There is no restriction on the location or number of members in a multicast group.
If necessary, a host can be a member of more than one multicast group at a time.
Therefore, the active status of a group and the number of group members vary
from time to time.
Devices run a multicast routing protocol (such as PIM-DM, PIM-SM, etc.) to
maintain their routing tables to forward multicast messages, and use the IGMP to
learn the status of the members within a group on their directly attached subnets.
A host can join or leave an IGMP group by sending corresponding IGMP Report
messages.
IP multicast is ideal for “one-to-multiple” multimedia applications.
1.1.1 IP Multicast Routing Implementation
There are the following multicast routing protocols:
IGMP: Runs between the routers and the hosts in a LAN to track the
membership of a group and learn the relation among members.
PIM-DM: A multicast routing protocol in dense mode, which runs between
multicast devices to establish the multicast routing table for forwarding.
PIM-SM: A multicast routing protocol in sparse mode, which runs between
multicast devices to establish the multicast routing table for forwarding.
DVMRP: Distance Vector Multicast Routing Protocol, which runs between