C++实现发送和接收自定义类型的链路层数据帧——绑定，目的地址不同于接收网卡

柔情只为你懂 2021-09-19 03:06 236阅读 0赞

**一 实战前准备**

1 准备两台虚拟机

A机配置

B机配置

**二 接收端**

1 代码

#include <stdio.h>  
    #include <string.h>  
    #include <errno.h>  
    #include <sys/types.h>   
    #include <sys/socket.h>  
    #include <netpacket/packet.h>  
    #include <net/if.h>  
    #include <net/if_arp.h>  
    #include <sys/ioctl.h>  
    #include <arpa/inet.h> //for htons
    #include <netinet/if_ether.h>   //for ethhdr
    #define LEN     60
    void print_str16(unsigned char buf[], size_t len)  
    {  
        int     i;  
        unsigned char   c;  
        if (buf == NULL || len <= 0)  
            return;  
        for (i = 0; i < len; i++) {  
            c = buf[i];  
            printf("%02x", c);  
        }  
        printf("\n");  
    }  
    void print_sockaddr_ll(struct sockaddr_ll *sa)  
    {  
        if (sa == NULL)  
            return;  
        printf("sll_family:%d\n", sa->sll_family);  
        printf("sll_protocol:%#x\n", ntohs(sa->sll_protocol));  
        printf("sll_ifindex:%#x\n", sa->sll_ifindex);  
        printf("sll_hatype:%d\n", sa->sll_hatype);  
        printf("sll_pkttype:%d\n", sa->sll_pkttype);  
        printf("sll_halen:%d\n", sa->sll_halen);  
        printf("sll_addr:"); print_str16(sa->sll_addr, sa->sll_halen);  
    }  
    int main()  
    {  
        int             result = 0, fd, n, count = 0;  
        char    buf[LEN];  
        struct sockaddr_ll      sa, sa_recv;  
        struct ifreq    ifr;  
        socklen_t       sa_len = 0;  
        char    if_name[] = "enp0s3";  
        struct ethhdr *eth; //定义以太网头结构体指针
      
    
        //create socket  
        fd = socket(PF_PACKET, SOCK_RAW, htons(0x8902));  
        if (fd < 0) {  
            perror("socket error\n");  
            return errno;  
        }  
        
        
        memset(&sa, 0, sizeof(sa));  
        sa.sll_family = PF_PACKET;  
        sa.sll_protocol = htons(0x8902);  
        
        // get flags   
        strcpy(ifr.ifr_name, if_name);  //必须先得到flags，才能再得到index
        result = ioctl(fd, SIOCGIFFLAGS, &ifr);  
        if (result != 0) {   
            perror("ioctl error, get flags\n");  
            return errno;  
        }        
        result = ioctl(fd, SIOCGIFINDEX, &ifr);        //get index  
        if (result != 0) {  
            perror("ioctl error, get index\n");  
            return errno;  
        }  
        sa.sll_ifindex = ifr.ifr_ifindex;  
        result = bind(fd, (struct sockaddr*)&sa, sizeof(struct sockaddr_ll));  //bind fd  
        if (result != 0) {  
            perror("bind error\n");  
            return errno;  
        }  
      
          //recvfrom  
        while (1) {  
            memset(buf, 0, sizeof(buf));  
            // 第5个和第6个参数没有用NULL，这样可以获得对端（发送端）的物理地址sockaddr_ll的内容
             n = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr *)&sa_recv, &sa_len);  
            //n = recvfrom(fd, buf, sizeof(buf), 0, NULL, NULL);    //如果不需要打印sa_recv内容，用NULL也可以
            if (n < 0) {  
                printf("sendto error, %d\n", errno);  
                return errno;  
            }  
            printf("******************* recvfrom msg %d ****************\n", ++count);  
            print_str16((unsigned char*)buf, n);     //打印数据帧的内容
            
            eth = (struct ethhdr*)buf;
            //从eth里提取目的mac、源mac、协议号
            printf("proto=0x%04x,dst mac addr:%02x:%02x:%02x:%02x:%02x:%02x\n", ntohs(eth->h_proto), eth->h_dest[0], eth->h_dest[1], eth->h_dest[2], eth->h_dest[3], eth->h_dest[4], eth->h_dest[5]);
            printf("proto=0x%04x,src mac addr:%02x:%02x:%02x:%02x:%02x:%02x\n", ntohs(eth->h_proto), eth->h_source[0], eth->h_source[1], eth->h_source[2], eth->h_source[3], eth->h_source[4], eth->h_source[5]);
            
            // 打印sockaddr_ll的内容
            print_sockaddr_ll(&sa_recv);  
            printf("sa_len:%d\n", sa_len);  
        }  
        return 0;  
    }

2 编译运行

[root@localhost test]# g++ recv.cpp -o recv
    [root@localhost test]# ./recv

**三 发送端**

1 代码

2 运行

[root@localhost test]# g++ send.cpp -o send
    [root@localhost test]# ./send
    0800278745350800270c3bd3890200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
    sendto msg 1, len 60
    sendto msg 2, len 60
    sendto msg 3, len 60

3 A机结果

A机没有收到数据包，这说明我们绑定enp0s3后，recv只等待接收发向enp0s3的数据帧，而send的数据帧是发向enp0s8的，因此recv收不到。