#include <stdio.h>
#include <sys/types.h>
#include <net/if_arp.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <string.h>

void print_eth_addr(const char* ip)
{
     int s;
     struct sockaddr_in *sin;
     struct arpreq a;
     struct in_addr addr;

     s = socket(AF_INET, SOCK_DGRAM,0);

     memset(&a, 0, sizeof(a));
     strcpy(a.arp_dev, "wlan0");
     sin = (struct sockaddr_in*)&(a.arp_pa);
     sin->sin_family = AF_INET;
     a.arp_flags = ATF_PUBL;

     inet_aton(ip, &addr);

     memcpy(&sin->sin_addr, &addr, sizeof(struct in_addr));

     if (ioctl(s,SIOCGARP,&a)) {
          perror("ioctl");
     }
     unsigned char* hw_addr = (unsigned char *) a.arp_ha.sa_data;
     printf("HWAddr found : %x:%x:%x:%x:%x:%x\n", hw_addr[0],
        hw_addr[1], hw_addr[2], hw_addr[3], hw_addr[4], hw_addr[5]);

}

Just change “wlan0″ for “eth0″ or your favorite network interface.

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