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Chapter 17 IPv4 Multicast Protocol
17.1 IPv4 Multicast Protocol Overview
This chapter will give an introduction to the configuration of IPv4 Multicast Protocol.
All IPs in this chapter are IPv4.
17.1.1 Introduction to Multicast
Various transmission modes can be adopted when the destination of packet
(including data, sound and video) transmission is the minority users in the network. One
way is to use Unicast mode, i.e. to set up a separate data transmission path for each
user; or, to use Broadcast mode, which is to send messages to all users in the network,
and they will receive the Broadcast messages no matter they need or not. For example, if
there are 200 users in a network who want to receive the same packet, then the
traditional solution is to send this packet for 200 times separately via Unicast to
guarantee the users who need the data can get all data wanted, or send the data in the
entire domain via Broadcast. Transferring the data in the whole range of network .The
users who need these datas can get directly from the network. Both modes waste a great
deal of valuable bandwidth resource, and furthermore, Broadcast mode goes against the
security and secrecy.
The emergence of IP Multicast technology solved this problem in time. The Multicast
source only sends out the message once, Multicast Routing Protocol sets up tree-routing
for Multicast data package, and then the transferred packet just starts to be duplicated
and distributed in the bifurcate crossing as far as possible. Thus the packet can be sent
to every user who needs it accurately and effectively.
It should be noticed that it is not necessary for Multicast source to join in Multicast
group. It sends data to some Multicast groups, but it is not necessarily a receiver of the
group itself. There can be more than one source sending packets to a Multicast group
simultaneously. There may exist routers in the network which do not support Multicast,
but a Multicast router can encapsulate the Multicast packets into Unicast IP packets with
tunnel mode to send them to the Multicast router next to it, which will take off the Unicast
IP header and continue the Multicast transmission process, thus a big alteration of
network structure is avoided. The primary advantages of Multicast are:
1) Enhance efficiency: reduce network traffic, lighten the load of server and CPU
