大多数时候，我们要根据需要去发送一些包，这里把发包代码添上，同时处理了头文件的引入。

sys/ioctl.h定义了ioctl函数及其所需要的宏;

arpa/inet.h 中定义了htons，之前htons编译时会有警告，是因为编译时没有找到定义;

netpacket/packet.h中定义了sockaddr 的相关结构体。

运行结果可以通过抓包工具看到，当发现包中写有'hello'时，就是我们的刚刚发的包了，从结果来看，大多数的目标地址是广播地址。

这里介绍两款不错的抓包工具，一个是commview,另一个是wireshark，后者要在属性中新增hardaddressc的源地址和目标地址列。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <linux/if_ether.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <netpacket/packet.h>

/**
 * Set misc mode for interface
 * \param if_name interface name we will set
 * \param sockfd the socket id we will set
 * \return 0 is success
 * */
int set_promisc (char *if_name, int sockfd)
{
    struct ifreq ifr;

    if (NULL == if_name)
        return -1;

    strcpy (ifr.ifr_name, if_name);
    if (0 != ioctl (sockfd, SIOCGIFFLAGS, &ifr))
    {
        printf ("Get interface flag failed\n");
        return -1;
    }

    /* add the misc mode */
    ifr.ifr_flags |= IFF_PROMISC;

    if (0 != ioctl (sockfd, SIOCSIFFLAGS, &ifr))
    {
        printf ("Set interface flag failed\n");
        return -1;
    }

    return 0;
}

/**
 * Send the package
 * \param the interface name that we will be send from
 * \param the destination mac address
 * \return 0 is success
 * */
int send_package (char *if_name, char *send_mac)
{
    int send_skt;
    struct sockaddr_ll s_ll;
    struct ifreq ifr;
   /* package size must above or equal (14 + 46 + 4) */
    char send_buffer[64] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
                             0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
                             0x08, 0x00 };

    if (NULL == if_name || NULL == send_mac)
        return -1;

    /* create send socket */
    if ((send_skt = socket (AF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0)
    {
        printf ("create send socket failed\n");
        return -1;
    }

    /* get the index of interface */
    strcpy (ifr.ifr_name, if_name);
    if (0 != ioctl (send_skt, SIOCGIFINDEX, &ifr))
    {
        printf ("get interface index failed\n");

        close(send_skt);
        return -1;
    }

    s_ll.sll_family = AF_PACKET;  /* AF_PACKET is same with PF_PACKET, the 
                                                        only different maybe A is mean Address,
                                                        and P is mean protocol, so here we use
                                                        Address to set sock address option */
    s_ll.sll_protocol = 0;  /* send any protocol packet */
    s_ll.sll_ifindex = ifr.ifr_ifindex;

    /* push the address and data into the package */
    memcpy (send_buffer, send_mac, 6);
    memcpy (send_buffer + 14, "hello", 5);

    /* bind the sock handle to the interface by index */
    if (0 != bind (send_skt, (struct sockaddr *) &s_ll, sizeof (s_ll)))
    {
        printf ("bind the send sockfd to interface failed\n");

        close(send_skt);
        return -1;
    }

    /* send buffer, it will be return buffer length that we have send */
    if (send (send_skt, send_buffer, sizeof (send_buffer), 0) < 0)
    {
        printf ("send package failed\n");

        close(send_skt);
        return -1;
    }

    close(send_skt);   

    return 0;
}

int main (int argc, char *argv[])
{
    int sockfd;
    int ret = 0;
    char buffer[1518] = {0};
    char *eth_head = NULL;
    char send_mac[6] = {0};

   if ((sockfd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0)
   {
       printf ("create socket failed\n");
       return -1;
   }

   if (0 != set_promisc ("eth0", sockfd))
   {
       printf ("Failed to set interface promisc mode\n");
   }

   while (1)
   {
        memset (buffer, 0x0, sizeof (buffer));
        ret = recvfrom (sockfd, buffer, sizeof (buffer), 0, NULL, NULL);
        printf ("recview package length : %d\n", ret);

        eth_head = buffer;
        printf ("PACKAGE START\n");
        /* get source and dectination mac address */
        printf ("dectination mac:%02x-%02x-%02x-%02x-%02x-%02x,"
                "source mac:%02x-%02x-%02x-%02x-%02x-%02x;\n", eth_head[0],
                eth_head[1], eth_head[2], eth_head[3], eth_head[4],
                eth_head[5], eth_head[6], eth_head[7], eth_head[8],
                eth_head[9], eth_head[10], eth_head[11]);
        printf ("eth_type:%02x%02x\n", eth_head[12], eth_head[13]);

        /* ARP protocol flag */
        if (0x08 == eth_head[12] && 0x06 == eth_head[13])
        {
            printf ("ARP source ip:%d.%d.%d.%d,destination ip:%d.%d.%d.%d;\n",
                    eth_head[28], eth_head[29], eth_head[30], eth_head[31],
                    eth_head[38], eth_head[39], eth_head[40], eth_head[41]);

            /* send a package to the source mac */
            memcpy (send_mac, eth_head, 6);
            if (0 != send_package ("eth0", send_mac))
            {
                printf ("say hello to %02x-%02x-%02x-%02x-%02x-%02x failed\n",
                        eth_head[0], eth_head[1], eth_head[2], eth_head[3],
                        eth_head[4], eth_head[5]);
            }
            else
            {
                printf ("say hello to %02x-%02x-%02x-%02x-%02x-%02x already\n",
                        eth_head[0], eth_head[1], eth_head[2], eth_head[3],
                        eth_head[4], eth_head[5]);
            }

        }
        /* IPv4 protocol flag */
        else if (0x08 == eth_head[12] && 0x00 == eth_head[13])
        {
            if (0x45 == eth_head[14])
            {
                printf ("IPv4 source ip:%d.%d.%d.%d,destination ip:%d.%d.%d."
                        "%d;\n", eth_head[26], eth_head[27], eth_head[28],
                        eth_head[29], eth_head[30], eth_head[31],
                        eth_head[32], eth_head[33]);

                /* send a package to the source mac */
                memcpy (send_mac, eth_head, 6);
                if (0 != send_package ("eth0", send_mac))
                {
                     printf ("say hello to %02x-%02x-%02x-%02x-%02x-%02x failed\n",
                           eth_head[0], eth_head[1], eth_head[2], eth_head[3],
                           eth_head[4], eth_head[5]);
                }
                else
                {
                    printf ("say hello to %02x-%02x-%02x-%02x-%02x-%02x already\n",
                            eth_head[0], eth_head[1], eth_head[2], eth_head[3],
                            eth_head[4], eth_head[5]);
                }

            }
            else
            {
                printf ("p_head:%02x\n", eth_head[14]);
            }
        }
        printf ("PACKAGE END\n");
   }

    close(sockfd);

    return 0;
}