Table of Contents
Advertisement
Chapter 19 Multicast protocol Configuration
19.1 Multicast Protocol Overview
19.1.1 Introduction to Multicast
When sending information (including data, voice and video) to a small number of users in the
network, there are several ways of transmission. For example, the unicast method that establishes a
separate data transmission channel for each user and the broadcast method which sends information
to all users in the network regardless of whether they need the information or not. Suppose 200
users in a network need to receive the same information, traditionally, the unicast method is
employed to sends the same information 200 times to ensure users requiring the data can get what
they need; or the information is broadcasted throughout the network so that users requiring the data
can obtain what they need directly from the network. Both methods waste a large amount of
precious bandwidth resource, and the broadcast method is unfavorable for security of information.
The advent of IP multicast technology solved this problem. Multicast source sends the information
only once, and the multicast routing protocol create a tree route for the multicast packet; the
information being transferred will start duplicating and distribution in the fork as fast as possible.
This way, the information can be sent to each user requiring it accurately and efficiently.
It should be noted that the multicast source is not necessarily a member of the multicast group.
When sending data to some multicast group, the sender itself is not necessarily a receiver of that
group. Multiple sources are allowed to send packets to the same multicast group at the same time.
There may be routers not support multicast in the network. Multicast routers can transfer the
multicast packets encapsulated in unicast IP packets in tunnel mode to the neighbor multicast routes,
the neighbor multicast routers will strip the unicast IP head can continue multicast transmission.
This way, large modification to the network structure can be avoided. The major benefits of
multicast are:
1)
Improved efficiency and reduced network traffic and server/CPU load.
2)
Improved performance and reduced unnecessary traffic.
Distributed application: enabling multiple point application.
3)
19.1.2 Multicast Address
The multicast packets uses Class D IP address as their destination addresses, ranging from 224.0.0.0
to 239.255.255.255. Class D addresses cannot be used in the source IP address field of an IP packet.
In unicast, the path a packet travels is from the source address to the destination address, and the
packet is transfer in the network hop-by-hop. However, in IP multicast, the destination address of a
packet is a group (group address) instead of one single address. All information receivers are
arranged in the same group. And once a receiver joins a multicast group, data sent to multicast
address will immediately start transferring to the receiver. All members in the group will receive the
packets. The membership for a multicast group is dynamic; the hosts can join and quit a multicast
EES4710BD 10 Slots L2/L3/L4 Chassis Switch
457
Advertisement
Table of Contents
Troubleshooting
