Acceso a las interfaces de red en Linux

---

/*****************************************************************************
* autor: Daniel Lerch
* url: http://daniellerch.com
******************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <malloc.h>
#include <ctype.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>
#include <net/if.h>
#include <sys/ioctl.h>

#define ETH_P_ARP 	0x0806 

/* Funcion de utiliadad para pasar una ip en formato u_int32_t a un char* */
char *inetaddr ( u_int32_t ip ) 
{
   struct in_addr in;
   in.s_addr = ip;
   return inet_ntoa(in);
}

int main ()
{
   struct ifreq if_data;
   int sockd;
   u_int8_t  local_mac[6];
   u_int32_t local_ip;
   u_int32_t local_netmask;
   u_int32_t local_broadcast;
   u_int32_t ip;

   /* Son necesarios privilegios de root */
   if (getuid () != 0)
   {
      perror ("You must be root. \n");
      exit (0);
   }

   /* Crea el socket */
   if ((sockd = socket (AF_INET, SOCK_PACKET, htons (ETH_P_ARP))) < 0)
   {
      perror("socket");
      exit (0);
   }

   /* Interfaz eth0 */
   strcpy (if_data.ifr_name, "eth0");

   /* Obtiene la MAC address */
   if (ioctl (sockd, SIOCGIFHWADDR, &if_data) < 0) {
      perror ("ioctl(): SIOCGIFHWADDR \n");
      exit(EXIT_FAILURE);
   }
   memcpy (local_mac, if_data.ifr_hwaddr.sa_data, 6);
   printf ("MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", 
            local_mac[0], local_mac[1], local_mac[2], 
            local_mac[3], local_mac[4], local_mac[5]);

   /* Obtiene la IP address */ 
   if (ioctl (sockd, SIOCGIFADDR, &if_data) < 0) {
      perror ("ioctl(); SIOCGIFADDR \n");
      exit(EXIT_FAILURE);
   }
   memcpy ((void *) &ip, (void *) &if_data.ifr_addr.sa_data + 2, 4);
   local_ip = ntohl (ip);
   printf ("IP: %s\n", inetaddr(ip));

   /* Obtiene la mascara de red */
   if (ioctl (sockd, SIOCGIFNETMASK, &if_data) < 0) {
      perror ("ioctl(): SIOCGIFNETMASK \n");
      exit(EXIT_FAILURE);
   }
   memcpy ((void *) &ip, (void *) &if_data.ifr_netmask.sa_data + 2, 4);
   local_netmask = ntohl (ip);
   printf ("NETMASK: %s\n", inetaddr(ip));

   /* Obtiene la direccion de broadcast */
   if (ioctl (sockd, SIOCGIFBRDADDR, &if_data) < 0) {
      perror ("ioctl(): SIOCGIFBRDADDR \n");
      exit(EXIT_FAILURE);
   }
   memcpy ((void *) &ip, (void *) &if_data.ifr_broadaddr.sa_data + 2, 4);
   local_broadcast = ntohl (ip);
   printf ("BROADCAST: %s\n", inetaddr(ip));

   return (0);
}