Internet multicast knowledge (1)

With the rapid development of the internet, more and more projects are using the internet for collaborative development. For some applications, such as distributed database development, many people in a Development Working Group need to collaborate and exchange information frequently in different locations. When the Group size is small, you only need to exchange information point-to-point. If the group size is large, point-to-point exchange information is a burden for both the network and the information sender, expensive. Although broadcast can be used for processing, broadcast to thousands of hosts on a network with millions of nodes is inefficient or even unlikely. A vast majority of machines are not interested in this information, causing information spam. Even worse, some hosts may mistakenly believe that this information is not interested and cannot be received. Therefore, we need a way for working groups with a large size and relatively small network connections to easily and quickly transmit information to each other. To this end, we have introduced the concept of IP multicast.
1. Meaning of hardware Multicast
1.1 meaning
Hardware multicast multicasting is a form of Multi-Point delivery. It uses hardware technology to communicate by using a large number of multicast addresses. When a group of machines need to communicate with each other, select a multicast address, configure the network interface hardware, and identify the multicast address to receive a copy of the group on the multicast address.
1.2 multicast and broadcast and unicast　
Broadcast broadcasting is the most common form of Multi-Point delivery. It delivers a copy of a group to each target site. It can be shipped by multiple single groups, or a copy of the group can be transferred through a separate connection until each receiver receives a copy.
In most networks, users send broadcast messages by dividing the group into a special reserved address, that is, the broadcast address, its main disadvantage is that it consumes a lot of Host resources and network resources.
Unicast unicasting) refers to data transmission with only one destination. In terms of the number of shipping destinations, unicast and broadcast can be considered as a subset of multicast. Unicast can be viewed as multicast that only includes one machine group; broadcast can be viewed as multicast that contains all machine groups. However, in terms of the delivery method of data packets, unicast, broadcast, and multicast are quite different.
2. Basic concepts of IP Multicast
2.1 meaning　
IP multicast IP multicasting is an abstraction of hardware multicast and an extension of the standard IP network layer protocol. It transmits IP data packets to a multicast group's multicast group host set based on the maximum shipping principle by using a specific IP multicast address. The basic method is: when a person sends data to a group of people, it does not have to send data to everyone, you only need to send the data to a specific reserved group address, and all users in the group can receive the data. In this way, the data can be sent to all the recipients only once, greatly reducing the network load and the sender's burden.
2.2 IP multicast members　
Each member of an IP Multicast can be distributed on an independent physical network regardless of the region. The relationship between members is dynamic. A host can join or exit a group at any time, it can also be a member of any group. The member relationship determines whether the host receives multicast data sent to the Group. At the same time, if you are not a member of a group, you can send multicast data packets to a group for greater flexibility.
The host involved in multicast can be divided into three levels: