arp.c

   1 #include <string.h>
   2 #include <unistd.h>
   3 #include <net/ethernet.h>
   4 #include <net/if_arp.h>
   5 #include <linux/if_packet.h>
   6
   7 #include "l2tpns.h"
   8
   9 /* Most of this code is based on keepalived:vrrp_arp.c */
  10
  11 struct arp_buf {
  12         struct ether_header eth;
  13         struct arphdr arp;
  14
  15         /* Data bit - variably sized, so not present in |struct arphdr| */
  16         unsigned char ar_sha[ETH_ALEN]; /* Sender hardware address */
  17         ipt ar_sip;                     /* Sender IP address. */
  18         unsigned char ar_tha[ETH_ALEN]; /* Target hardware address */
  19         ipt ar_tip;                     /* Target ip */
  20 } __attribute__((packed));
  21
  22 void sendarp(int ifr_idx, const unsigned char* mac, ipt ip)
  23 {
  24         int fd;
  25         struct sockaddr_ll sll;
  26         struct arp_buf buf;
  27
  28         /* Ethernet */
  29         memset(buf.eth.ether_dhost, 0xFF, ETH_ALEN);
  30         memcpy(buf.eth.ether_shost, mac, ETH_ALEN);
  31         buf.eth.ether_type = htons(ETHERTYPE_ARP);
  32
  33         /* ARP */
  34         buf.arp.ar_hrd = htons(ARPHRD_ETHER);
  35         buf.arp.ar_pro = htons(ETHERTYPE_IP);
  36         buf.arp.ar_hln = ETH_ALEN;
  37         buf.arp.ar_pln = 4; //IPPROTO_ADDR_LEN;
  38         buf.arp.ar_op = htons(ARPOP_REQUEST);
  39
  40         /* Data */
  41         memcpy(buf.ar_sha, mac, ETH_ALEN);
  42         memcpy(&buf.ar_sip, &ip, sizeof(ip));
  43         memcpy(buf.ar_tha, mac, ETH_ALEN);
  44         memcpy(&buf.ar_tip, &ip, sizeof(ip));
  45
  46         /* Now actually send the thing */
  47         fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
  48
  49         memset(&sll, 0, sizeof(sll));
  50         sll.sll_family = AF_PACKET;
  51         strncpy(sll.sll_addr, mac, sizeof(sll.sll_addr)); /* Null-pad */
  52         sll.sll_halen = ETH_ALEN;
  53         sll.sll_ifindex = ifr_idx;
  54
  55         sendto(fd, &buf, sizeof(buf), 0, (struct sockaddr*)&sll, sizeof(sll));
  56 }