arp.c

   1 // L2TPNS: arp
   2
   3 char const *cvs_id_arp = "$Id: arp.c,v 1.3 2004-06-28 02:43:13 fred_nerk Exp $";
   4
   5 #include <string.h>
   6 #include <unistd.h>
   7 #include <net/ethernet.h>
   8 #include <net/if_arp.h>
   9 #include <linux/if_packet.h>
  10
  11 #include "l2tpns.h"
  12
  13 /* Most of this code is based on keepalived:vrrp_arp.c */
  14
  15 struct arp_buf {
  16         struct ether_header eth;
  17         struct arphdr arp;
  18
  19         /* Data bit - variably sized, so not present in |struct arphdr| */
  20         unsigned char ar_sha[ETH_ALEN]; /* Sender hardware address */
  21         ipt ar_sip;                     /* Sender IP address. */
  22         unsigned char ar_tha[ETH_ALEN]; /* Target hardware address */
  23         ipt ar_tip;                     /* Target ip */
  24 } __attribute__((packed));
  25
  26 void sendarp(int ifr_idx, const unsigned char* mac, ipt ip)
  27 {
  28         int fd;
  29         struct sockaddr_ll sll;
  30         struct arp_buf buf;
  31
  32         /* Ethernet */
  33         memset(buf.eth.ether_dhost, 0xFF, ETH_ALEN);
  34         memcpy(buf.eth.ether_shost, mac, ETH_ALEN);
  35         buf.eth.ether_type = htons(ETHERTYPE_ARP);
  36
  37         /* ARP */
  38         buf.arp.ar_hrd = htons(ARPHRD_ETHER);
  39         buf.arp.ar_pro = htons(ETHERTYPE_IP);
  40         buf.arp.ar_hln = ETH_ALEN;
  41         buf.arp.ar_pln = 4; //IPPROTO_ADDR_LEN;
  42         buf.arp.ar_op = htons(ARPOP_REQUEST);
  43
  44         /* Data */
  45         memcpy(buf.ar_sha, mac, ETH_ALEN);
  46         memcpy(&buf.ar_sip, &ip, sizeof(ip));
  47         memcpy(buf.ar_tha, mac, ETH_ALEN);
  48         memcpy(&buf.ar_tip, &ip, sizeof(ip));
  49
  50         /* Now actually send the thing */
  51         fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
  52
  53         memset(&sll, 0, sizeof(sll));
  54         sll.sll_family = AF_PACKET;
  55         strncpy(sll.sll_addr, mac, sizeof(sll.sll_addr) - 1);
  56         sll.sll_halen = ETH_ALEN;
  57         sll.sll_ifindex = ifr_idx;
  58
  59         sendto(fd, &buf, sizeof(buf), 0, (struct sockaddr*)&sll, sizeof(sll));
  60         close(fd);
  61 }