Basic concepts of IP Multicast

D Class is IP Multicast address , The scope is 224.0.0.0 ~ 239.255.255.255. One IP message , If the destination address is unicast IP Address , It is called unicast IP message ; If it's multicast IP Address , It is called multicast IP message ; If it's radio IP Address , It is called broadcast IP message .
send out IP When the message , If it's unicast IP message , Then this transmission method is called IP Unicast mode , abbreviation IP unicast .
If you are sending multicast IP message , Then this transmission method is called IP Multicast mode , abbreviation IP Multicast .
If it's a broadcast IP message , Then this transmission method is called IP The way of broadcasting , abbreviation IP radio broadcast .
IP Unicast is a point-to-point communication mode , and IP Multicast is a point to multipoint communication mode . When a sender needs to send exactly the same information to multiple receivers at the same time , If unicast mode is adopted , Then the network needs to transmit a large number of messages , by comparison , Using multicast can greatly reduce the number of messages to be transmitted , So as to save a lot of network resources
In multicast mode , Multicast packets are transmitted from the information source to many end users along the tree route established by multicast routing protocol . In the process , Only members of the multicast group can receive and process messages of the multicast group , For members who are not members of the multicast group , Or the message of the multicast group cannot be received , Or discard it directly after receiving it .
IP Broadcast is also a point to multipoint communication mode , but IP Multicast can span network segments , and IP Broadcasting can only be limited to one network segment .

R1 As a gateway device ,PC4 As a network management terminal , Direct connection R1 On , Other PC Access switch SW1. Through multicast server MCS1 Play video on , Observe each PC Whether the video data can be received .

Interface IP Configuration omitted
1. Observe unicast mode ：
Purpose of unicast message IP An address can only identify a unique recipient , Only the recipient can receive and process the IP message ; Other recipients either cannot receive this message , Or it will not be processed after receiving it , But directly discard .
stay R1 Use unicast on IP 10.0.1.1 As a destination address ping operation , Respectively in PC1,PC2,PC3 Of E0/0/1 Capture packets on the interface to check the reception .

Can be observed ,PC2,PC3 Didn't receive ICMP news , Only PC1 received . If 3 All users need to receive ping package , You need to in R1 Upper use 3 platform PC The unicast of IP The address to send 3 Time ping package . In unicast mode , The number of messages to be transmitted in the network is directly proportional to the number of users . The more users , The more messages containing the same information in the network , It wastes the of network equipment CPU Resources waste network bandwidth resources .

2. Observe the broadcast mode ：
A broadcast IP The address identifies all network devices in a certain network segment , Each network device in the network segment will receive and process the broadcast message of the network segment .
stay R1 On the configuration RIPV1 agreement , send R1 Send by broadcast RIP message , And then in PC1,PC2,PC3 Of E0/0/1 Interface to check message reception .
[R1]rip 1
[R1-rip-1]network 10.0.0.0

You can see PC1,PC2,PC3 received R1 Sent by broadcast RIP message .
Only in the same broadcast mode , Can't cross network segment , Cannot distinguish recipients .

3. Observe the multicast mode ：
Use multicast , Only members who join the multicast group can receive and process the messages of the multicast group , For members who are not members of the multicast group , Or the message of the multicast group cannot be received , Or discard it directly after receiving it .
stay R1 Complete the basic multicast configuration on ; Enable multicast function in global mode ,G0/0/0 Enable the multicast function under the interface , stay G0/0/1,G0/0/2 Enable multicast function and IGMP function .
[R1]multicast routing-enable
[R1]int g0/0/0
[R1-GigabitEthernet0/0/0]pim dm
[R1-GigabitEthernet0/0/0]int g0/0/1
[R1-GigabitEthernet0/0/1]pim dm
[R1-GigabitEthernet0/0/1]igmp enable
[R1-GigabitEthernet0/0/1]int g0/0/2
[R1-GigabitEthernet0/0/2]pim dm
[R1-GigabitEthernet0/0/2]igmp enable

Multicast server MCS1 Use VLC Send multicast by playing video . Click on ENSP Set in the upper right corner , Select tool settings , Set up VLC Software path to .

open MCS1 Multicast server , Configuration basic configuration

Click multicast source , Select a video file , Configure multicast group IP Address , Multicast group MAC Address . Click on the run , This time it will pass VLC Play the video file we selected .

stay PC1 Upper use IGMPV2 Join in 224.1.1.1 Multicast group , start-up VLC, Click to add , You can play the video of the multicast source .

stay PC1 Of E0/0/1 Interface packet capture observed UDP Video data .