3Com Router User Manual

VII
MULTICAST
Chapter 33IP Multicast
Chapter 34Configuring IGMP
Chapter 35Configuring PIM-DM
Chapter 36Configuring PIM-SM 

498 

33
IP MULTICAST
This chapter covers the following topics:
■IP Multicast Overview
■IP Multicast Addresses
■IP Multicast Features
■IP Multicast Routing Protocols
■IP Multicast Packet Forwarding
■IP Multicast Application
IP Multicast OverviewWhen the destination addresses carrying information (data, voice, and video) 
transmit with only a few subscribers in the network, multiple transmission 
methods such as unicast and broadcast can be employed. Unicast transmission 
means establishing a separate data...

500CHAPTER 33: IP MULTICAST
Class D address is 1110, the range of the multicast addresses is from 224.0.0.0 to 
239.255.255.255. 
The multicast group can be either permanent or temporary. The permanent group 
has a constant group address assigned by IANA, while the number of members in 
the group can be random, even zero. Temporary multicast groups can use that 
group address, which is not reserved, but the number of members in the 
temporary multicast group cannot be zero. 
The range and meaning of...

IP Multicast Routing Protocols501
the IP multicast environment, the destination address of a data packet is not one 
address but a group, forming a group address. All the information receivers are 
added to a group, and once they access the group, data flowing to the destination 
address begin to transmit to the receivers of that particular group. All the group 
members can receive the data packet. Therefore, to get the data packet, they have 
to become group members first. The data packet transmitter is...

502CHAPTER 33: IP MULTICAST
Multicast Routing 
ProtocolThe group address in the multicast protocol is a virtual address. Therefore, unlike 
unicast, data packets cannot be routed directly from the data source to the 
specific destination address. The multicast application program sends the data 
packet to a group of receivers instead of a single receiver . 
Multicast routing establishes a cyclic data transmission path from one data source 
end to multiple receiving ends. The task of the multicast routing...

IP Multicast Packet Forwarding503
The transmitting end is first registered at the RP if it needs to send data to a 
specific address, and then sends the data to the RP. Once data reaches the RP, 
multicast data packets are duplicated and sent to receivers who are interested in 
getting them along the distribution tree path. The duplication only occurs at the 
crotch of the distribution tree. This process can automatically repeat until the data 
packets finally arrive at the destination point. 
IP...

504CHAPTER 33: IP MULTICAST 

34
CONFIGURING IGMP 
This chapter covers the following topics:
■IGMP Overview
■Configuring IGMP
■Displaying and Debugging IGMP
■IGMP Configuration Example
IGMP OverviewThe Internet Group Management Protocol (IGMP) is a protocol that is responsible 
for the IP multicast member management among the TCP/IP protocol family. It is 
the basis for IP multicast, and it is used to establish and maintain multicast 
membership between the IP hosts and the multicast routers directly adjacent to 
the hosts. IGMP does...

506CHAPTER 34: CONFIGURING IGMP
IGMP is asymmetric between hosts and routers. The host responds to the IGMP 
query message of the multicast router, and makes a response in the membership 
report message. The router periodically sends a general query message. Then it 
determines, based on the response message received, whether a specific group 
has a host access on its own subnet. Meanwhile, when a router exits from a 
group, it sends a message to the multicast router when it exits. When it receives 
the...