Broadcast, multicast, unicast

One . radio broadcast

1.1 Concept

Home page socket There is only one receiver for Jianshao's packet sending method , be called unicast

If it is sent to all hosts in the LAN at the same time , be called radio broadcast

If it is sent to some hosts in the LAN , be called Multicast

Be careful ： Only one sending method can be selected for the same socket .

User datagram only ( Use UDP agreement ) Socket to broadcast

1.2 Broadcast address

         With 192.168.1.0 (255.255.255.0) Network segment as an example , The largest host address 192.168.1.255 The data packets sent to the address representing the broadcast address of the network segment are received by all hosts ,255.255.255.255 Represents the broadcast address in all network segments .

Broadcast can be sent to all hosts , Because of the broadcast mac Special address , For all ff, ip The address is also special , It is broadcast ip Address , Send such packets to the switch first , Then it is sent to all hosts by the switch . Every host in the LAN can receive this packet , With UDP For example , The network card receives this packet , Check the link layer first , Purpose of discovery mac The address is the broadcast address , You can use the , To the network layer , Find out ip The address is broadcast ip Address , It is also allowed to pass , To the transport layer , As long as the destination port number matches , Then you can call the application layer for processing .

1.3 Broadcasting process

sender ：

Create socket socket( )

Set to allow sending broadcast permission setsockopt( )

Fill the broadcast information structure sockaddr_in

send data sendto( )

The receiver ：

Create socket socket( )

Fill the broadcast information structure sockaddr_in

Bind the socket to the broadcast information structure bind( )

receive data recvfrom( )

1.4 The code realizes broadcasting

Code instructions ： This code is to achieve a receive a send , The server receives , The client sends , The code is compared with the previous homepage socket It's almost a change in the way , Set up a broadcast , If you need to know , Please refer to the home page socket The article , Thank you for watching .

Set the way of broadcasting :

int on = 1;
setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on));

Server code

#include <stdio.h>
#include <sys/types.h>       
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(3 != argc){
        printf("Usage : %s <ip> <port>\n", argv[0]);
        return -1;
    }

    // Create user datagram socket 
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill the broadcast information structure 
    struct sockaddr_in serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    // The port number can be arbitrarily specified 
    serveraddr.sin_port = htons(atoi(argv[2]));
    //ip The address must be broadcast ip Address 
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    // binding 
    if(-1 == bind(sockfd, (struct sockaddr *)&serveraddr, serveraddr_len)){
        ERRLOG("bind error");
    }

    // Define the structure to save the information of the other party 
    struct sockaddr_in client_addr;
    memset(&client_addr, 0, sizeof(client_addr));
    socklen_t client_addr_len = sizeof(client_addr);

    char buff[128] = {0};
    // Receive data circularly 
    while(1){
        if(-1 == recvfrom(sockfd, buff, 128, 0, (struct sockaddr *)&client_addr, &client_addr_len)){
            ERRLOG("recvfrom error");
        }
        printf(" client [%s:%d] Send data [%s]\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buff);
        memset(buff, 0, 128);
    }

    close(sockfd);

    return 0;
}

Client code

#include <stdio.h>
#include <sys/types.h>        
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(3 != argc){
        printf("Usage : %s <ip> <port>\n", argv[0]);
        return -1;
    }
    // Create user datagram socket 
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill the broadcast information structure 
    struct sockaddr_in serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    // The port number can be arbitrarily specified 
    serveraddr.sin_port = htons(atoi(argv[2]));
    //ip The address must be broadcast ip Address 
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    // Set to allow broadcasting 
    int on = 1;
    if(-1 == setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on))){
        ERRLOG("setsockopt error");
    }

    char buff[128] = {0};

    // Loop data 
    while(1){
        fgets(buff, 128, stdin);
        buff[strlen(buff)-1] = '\0';
        if(-1 == sendto(sockfd, buff, 128, 0, (struct sockaddr *)&serveraddr, serveraddr_len)){
            ERRLOG("sendto error");
        }
        memset(buff, 0, 128);
    }

    return 0;
}

Two . Multicast

2.1 Concept

Unicast can only be sent to one receiver . Broadcast to all hosts . Too many broadcasts will take up a lot of network bandwidth , Cause a broadcast storm , Affect normal communication . Multicast ( Also known as multicast ) It's a compromise . Only hosts that join a multicast group can receive data . Multicast can be sent to multiple hosts , It can also avoid bringing too much load like broadcasting ( Each host must go to the transport layer to determine whether the broadcast packet needs to be processed ).

2.2 Multicast address

D Class address （ Multicast address ） Regardless of network address and host address , The first 1 Before byte 4 The bit is fixed to 1110

The address range of the anchor :224.0.0.1 – 239.255.255.255

2.3 Multicast process

sender ：

Create socket socket( )

Fill the multicast information structure sockaddr_in

send data sendto( )

The receiver ：

Create socket scoket( )

Fill the multicast information structure sockaddr_in

Bind the socket to the multicast information structure bind( )

Set to join the multicast group setsockopt( )

receive data recvfrom( )

2.3 Set join multicast group

// Use the following structure 
struct ip_mreqn {
    struct in_addr imr_multiaddr; /* Multicast group ip Address */
    struct in_addr imr_address;   /* Local ip Address */
    int            imr_ifindex;   /* Interface index  0 Represents any interface */
};

struct ip_mreqn  my_mreqn;
// fill 
setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &my_mreqn, sizeof(my_mreqn));

2.4 Code implementation

The server （ The receiver ）：

#include <stdio.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(3 != argc){
        printf("Usage : %s <ip> <port>\n", argv[0]);
        return -1;
    }

    // Create user datagram socket 
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill the broadcast information structure 
    struct sockaddr_in serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    // The port number can be arbitrarily specified 
    serveraddr.sin_port = htons(atoi(argv[2]));
    //ip The address is multicast group ip Address !!！！！
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    // Bind socket with   Multicast information structure 
    if(-1 == bind(sockfd, (struct sockaddr *)&serveraddr, serveraddr_len)){
        ERRLOG("bind error");
    }

    // Set join multicast group 
    struct ip_mreqn my_mreqn;
    memset(&my_mreqn, 0, sizeof(my_mreqn));
    my_mreqn.imr_multiaddr.s_addr = inet_addr(argv[1]);
    my_mreqn.imr_address.s_addr = inet_addr("192.168.60.109");
    my_mreqn.imr_ifindex = 0;// Any interface 
    if(-1 == setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &my_mreqn, sizeof(my_mreqn))){
        ERRLOG("setsockopt error");
    }

    // Define the structure to save the information of the other party 
    struct sockaddr_in client_addr;
    memset(&client_addr, 0, sizeof(client_addr));
    socklen_t client_addr_len = sizeof(client_addr);

    char buff[128] = {0};
    // Receive data circularly 
    while(1){
        if(-1 == recvfrom(sockfd, buff, 128, 0, (struct sockaddr *)&client_addr, &client_addr_len)){
            ERRLOG("recvfrom error");
        }
        printf(" client [%s:%d] Send data [%s]\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buff);
        memset(buff, 0, 128);
    }

    close(sockfd);

    return 0;
}

client （ Send ）：

#include <stdio.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(3 != argc){
        printf("Usage : %s <ip> <port>\n", argv[0]);
        return -1;
    }
    // Create user datagram socket 
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill the broadcast information structure 
    struct sockaddr_in serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    // The port number can be arbitrarily specified 
    serveraddr.sin_port = htons(atoi(argv[2]));
    //ip Address broadcast address 
    //224.0.0.1 ~ 239.255.255.255
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    char buff[128] = {0};

    // Loop data 
    while(1){
        fgets(buff, 128, stdin);
        buff[strlen(buff)-1] = '\0';
        if(-1 == sendto(sockfd, buff, 128, 0, (struct sockaddr *)&serveraddr, serveraddr_len)){
            ERRLOG("sendto error");
        }
        memset(buff, 0, 128);
    }

    return 0;
}