arp request

arp.c

#include <string.h>
#include <stdio.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <sys/param.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <netdb.h>

#define DEVICE     "enp7s0"
#define SRC_MAC    0x40,0xb0,0x76,0x47,0x8f,0x9a
#define SRC_IP4    192,168,1,33
#define ROUTE_IP4  192,168,1,1

#define ARP_PRO_IP 0x0800

typedef unsigned char u8;
typedef unsigned short u16;

typedef struct __received {
  u8 skip[12];
  u16 type;
  u8 skip1[8];
  u8 sha[6];
  u8 skip2[4+6];
  u8 tpa[4];
} recvhdr;

int main(void)
{
  struct sockaddr_ll  sll;
  struct ifreq        ifr;
  int                 fd, n;
  char                device[] = DEVICE;
  size_t              pktlen;
  u8                  pkt[100];
  u8                  received[100];
  recvhdr            *r=NULL;
  u8                  res[6];

  /* mac hdr*/
  u8 mac_dst[6] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
  u8 mac_src[6] = {SRC_MAC};
  u16 mac_type  = htons(ETHERTYPE_ARP);

  /* arp hdr*/
  u16 arp_hdr = htons(ARPHRD_ETHER);
  u16 arp_pro = htons(ARP_PRO_IP);
  u8  arp_hln = 6;                    /* mac addr len */
  u8  arp_pln = 4;                    /* ipv4 addr len */
  u16 arp_op  = htons(ARPOP_REQUEST); /* operation */

  /* arp request hdr*/
  u8 sha[6] = {SRC_MAC};
  u8 spa[4] = {SRC_IP4};
  u8 tha[6] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
  u8 tpa[4] = {192, 168, 1, 1};

  /* copy */
  memcpy(pkt,             mac_dst,  6);
  memcpy(pkt+6,           mac_src,  6);
  memcpy(pkt+6+6,        &mac_type, 2);
  memcpy(pkt+14,         &arp_hdr,  2);
  memcpy(pkt+14+2,       &arp_pro,  2);
  memcpy(pkt+14+2+2,     &arp_hln,  1);
  memcpy(pkt+14+2+2+1,   &arp_pln,  1);
  memcpy(pkt+14+2+2+1+1, &arp_op,   2);
  memcpy(pkt+14+8,        sha,      6);
  memcpy(pkt+14+8+6,      spa,      4);
  memcpy(pkt+14+8+6+4,    tha,      6);
  memcpy(pkt+14+8+6+4+6,  tpa,      4);

  /* machdr + arphdr + arpreqhdr */
  pktlen=14+8+20;

  fd=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
  if (fd<0)
    return -1;

  n=1;
  if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &n, sizeof(n))<0)
    goto fail;

  strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
  if (ioctl(fd, SIOCGIFINDEX, &ifr) < 0)
    goto fail;

  sll.sll_family = AF_PACKET;
  sll.sll_ifindex = ifr.ifr_ifindex;
  sll.sll_protocol=ETHERTYPE_ARP;

  sendto(fd, pkt, pktlen, 0, (struct sockaddr*)&sll, sizeof(sll));

  for (;;) {
    if ((recv(fd, received, 100, 0))==-1)
      goto fail;
    r=(recvhdr*)received;
    if (ntohs(r->type)==ETHERTYPE_ARP) {
#define CMP(x) (r->tpa[(x)]==spa[(x)])
      if (CMP(0)&&CMP(1)&&CMP(2)&&CMP(3)) {
        memcpy(res, r->sha, 6);
        break;
      }
#undef CMP
    }
  }
  printf("dst mac is %02x:%02x:%02x:%02x:%02x:%02x\n",
      res[0], res[1], res[2], res[3], res[4], res[5]);

  close(fd);
  return 0;

fail:
  close(fd);
  return -1;
}