arp.c

   1 // L2TPNS: arp
   2
   3 #include <string.h>
   4 #include <unistd.h>
   5 #include <net/ethernet.h>
   6 #include <net/if_arp.h>
   7 #include <linux/if_packet.h>
   8
   9 #include "l2tpns.h"
  10
  11 /* Most of this code is based on keepalived:vrrp_arp.c */
  12
  13 struct arp_buf {
  14         struct ether_header eth;
  15         struct arphdr arp;
  16
  17         /* Data bit - variably sized, so not present in |struct arphdr| */
  18         unsigned char ar_sha[ETH_ALEN]; /* Sender hardware address */
  19         in_addr_t ar_sip;               /* Sender IP address. */
  20         unsigned char ar_tha[ETH_ALEN]; /* Target hardware address */
  21         in_addr_t ar_tip;               /* Target ip */
  22 } __attribute__((packed));
  23
  24 void sendarp(int ifr_idx, const unsigned char* mac, in_addr_t ip)
  25 {
  26         int fd;
  27         struct sockaddr_ll sll;
  28         struct arp_buf buf;
  29
  30         CSTAT(sendarp);
  31         STAT(arp_sent);
  32
  33         /* Ethernet */
  34         memset(buf.eth.ether_dhost, 0xFF, ETH_ALEN);
  35         memcpy(buf.eth.ether_shost, mac, ETH_ALEN);
  36         buf.eth.ether_type = htons(ETHERTYPE_ARP);
  37
  38         /* ARP */
  39         buf.arp.ar_hrd = htons(ARPHRD_ETHER);
  40         buf.arp.ar_pro = htons(ETHERTYPE_IP);
  41         buf.arp.ar_hln = ETH_ALEN;
  42         buf.arp.ar_pln = 4; //IPPROTO_ADDR_LEN;
  43         buf.arp.ar_op = htons(ARPOP_REQUEST);
  44
  45         /* Data */
  46         memcpy(buf.ar_sha, mac, ETH_ALEN);
  47         memcpy(&buf.ar_sip, &ip, sizeof(ip));
  48         memcpy(buf.ar_tha, mac, ETH_ALEN);
  49         memcpy(&buf.ar_tip, &ip, sizeof(ip));
  50
  51         /* Now actually send the thing */
  52         fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
  53
  54         memset(&sll, 0, sizeof(sll));
  55         sll.sll_family = AF_PACKET;
  56         memcpy(sll.sll_addr, mac, sizeof(sll.sll_addr) - 1);
  57         sll.sll_halen = ETH_ALEN;
  58         sll.sll_ifindex = ifr_idx;
  59
  60         sendto(fd, &buf, sizeof(buf), 0, (struct sockaddr*)&sll, sizeof(sll));
  61         close(fd);
  62 }