C++实现发送和接收自定义类型的链路层数据帧——不绑定实战

缺乏、安全感 2021-09-19 03:06 329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_recv;  
        struct ifreq    ifr;  
        socklen_t       sa_len = 0;  
        //char    if_name[] = "eno16777736";  
        struct ethhdr *eth; //定义以太网头结构体指针
      
        //创建套接字，自定义协议0x8902
        fd = socket(PF_PACKET, SOCK_RAW, htons(0x8902));  
        if (fd < 0) {  
            perror("socket error\n");  
            return errno;  
        }  
    
        // 开始等待接收数据  
        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 编译并运行

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

**三 发送端**

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
      
    #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");  
    }  
    int main()  
    {  
        int             result = 0;  
        int             fd, n, count = 3, nsend = 0;  //count表示发送3个数据包
        char    buf[LEN];  
        struct sockaddr_ll      sa;  
        struct ifreq    ifr;  
        char    if_name[] = "enp0s3";  //本机要发送数据的网卡名称
        //对应enp0s3 ，192.168.0.110的网卡
        char    dst_mac[6] = { 0x08,0x00,0x27,0x60,0x7b,0x7f };
        char    src_mac[6];  
        short   type = htons(0x8902);  
      
        memset(&sa, 0, sizeof(struct sockaddr_ll));  
        memset(buf, 0, sizeof(buf));  
      
        //创建套接字  
        fd = socket(PF_PACKET, SOCK_RAW, htons(0x8902));  
        if (fd < 0) {  
            printf("socket error, %d\n", errno);  
            return errno;  
        }  
      
        //获得网卡索引号  
        strcpy(ifr.ifr_name, if_name);  
        result = ioctl(fd, SIOCGIFINDEX, &ifr);  
        if (result != 0) {  
            printf("get mac index error, %d\n", errno);  
            return errno;  
        }  
        sa.sll_ifindex = ifr.ifr_ifindex;  //赋值给物理层地址
      
        //得到源MAC地址，即本机要发送数据的网卡MAC地址
        result = ioctl(fd, SIOCGIFHWADDR, &ifr);  
        if (result != 0) {  
            printf("get mac addr error, %d\n", errno);  
            return errno;  
        }  
        
        memcpy(src_mac, ifr.ifr_hwaddr.sa_data, 6);  
      
        //设置数据给以太网帧头  
        memcpy(buf, dst_mac, 6);  
        memcpy(buf + 6, src_mac, 6);  
        memcpy(buf + 12, &type, 2);  
      
        print_str16((unsigned char*)buf, sizeof(buf));   //打印发要送的数据帧
        //准备发送数据
        while (count-- > 0) {  
            n = sendto(fd, buf, sizeof(buf), 0, (struct sockaddr *)&sa, sizeof(struct sockaddr_ll));  
            if (n < 0) {  
                printf("sendto error, %d\n", errno);  
                return errno;  
            }  
            printf("sendto msg %d, len %d\n", ++nsend, n);  
        }  
        return 0;  
    }

2 编译并运行

[root@localhost test]# ./send
    080027607b7f0800270c3bd3890200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
    sendto msg 1, len 60
    sendto msg 2, len 60
    sendto msg 3, len 60

此时接收端收到结果如下：

[root@localhost test]# ./recv
    ******************* recvfrom msg 1 ****************
    080027607b7f0800270c3bd3890200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
    proto=0x8902,dst mac addr:08:00:27:60:7b:7f
    proto=0x8902,src mac addr:08:00:27:0c:3b:d3
    sll_family:0
    sll_protocol:0
    sll_ifindex:0
    sll_hatype:0
    sll_pkttype:0
    sll_halen:0
    sll_addr:sa_len:18
    ******************* recvfrom msg 2 ****************
    080027607b7f0800270c3bd3890200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
    proto=0x8902,dst mac addr:08:00:27:60:7b:7f
    proto=0x8902,src mac addr:08:00:27:0c:3b:d3
    sll_family:17
    sll_protocol:0x8902
    sll_ifindex:0x2
    sll_hatype:1
    sll_pkttype:0
    sll_halen:6
    sll_addr:0800270c3bd3
    sa_len:18
    ******************* recvfrom msg 3 ****************
    080027607b7f0800270c3bd3890200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
    proto=0x8902,dst mac addr:08:00:27:60:7b:7f
    proto=0x8902,src mac addr:08:00:27:0c:3b:d3
    sll_family:17
    sll_protocol:0x8902
    sll_ifindex:0x2
    sll_hatype:1
    sll_pkttype:0
    sll_halen:6
    sll_addr:0800270c3bd3
    sa_len:18

**四 说明**

默认情况下，从任何接口收到符合指定协议（包括自定义协议号）的所有数据报文都会被传送到原始PACKET套接口，而使用bind系统调用并以一个sockaddr\_ll结构体对象将PACKET套接口与某个网络接口相绑定，可以使我们的PACKET原始套接字只接收指定接口的数据报文。