Get MAC address using IP address via ARP using UDP sockets

arp.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

int main() {
  struct sockaddr_in sin = {0};
  sin.sin_family = AF_INET;

  char ip[20];
  printf("Enter IP address: ");
  scanf("%s", ip);
  if(inet_pton(AF_INET, ip, &sin.sin_addr) == 0) {
    printf("Invalid IP address = %s entered.\n", ip);
    return 1;
  }

  struct arpreq myarp = {{0}};
  memcpy(&myarp.arp_pa, &sin, sizeof(myarp.arp_pa));
  strcpy(myarp.arp_dev, "eth0");

  int sd;
  if ((sd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
    perror("socket");
    return 1;
  }

  printf("Sending ARP request...\n");
  if(ioctl(sd, SIOCGARP, &myarp) < 0) {
    printf("No entry in ARP cache for %s!\n",ip);
    exit(1);
  }

  close(sd);

  unsigned char *mac = myarp.arp_ha.sa_data;
  printf("Received ARP reply...\n");
  printf("MAC address for %s is ", ip);
  printf("%02X:%02X:%02X:%02X:%02X:%02X\n",
      mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

  return 0;
}

Short URL: https://git.io/arp_mac