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 #include <linux/rtnetlink.h>
   9 #include <netinet/ip6.h>
  10
  11 #include "dhcp6.h"
  12 #include "l2tpns.h"
  13
  14 /* Most of this code is based on keepalived:vrrp_arp.c */
  15
  16 struct arp_buf {
  17         struct ether_header eth;
  18         struct arphdr arp;
  19
  20         /* Data bit - variably sized, so not present in |struct arphdr| */
  21         unsigned char ar_sha[ETH_ALEN]; /* Sender hardware address */
  22         in_addr_t ar_sip;               /* Sender IP address. */
  23         unsigned char ar_tha[ETH_ALEN]; /* Target hardware address */
  24         in_addr_t ar_tip;               /* Target ip */
  25 } __attribute__((packed));
  26
  27 void sendarp(int ifr_idx, const unsigned char* mac, in_addr_t ip)
  28 {
  29         int fd;
  30         struct sockaddr_ll sll;
  31         struct arp_buf buf;
  32
  33         CSTAT(sendarp);
  34         STAT(arp_sent);
  35
  36         /* Ethernet */
  37         memset(buf.eth.ether_dhost, 0xFF, ETH_ALEN);
  38         memcpy(buf.eth.ether_shost, mac, ETH_ALEN);
  39         buf.eth.ether_type = htons(ETHERTYPE_ARP);
  40
  41         /* ARP */
  42         buf.arp.ar_hrd = htons(ARPHRD_ETHER);
  43         buf.arp.ar_pro = htons(ETHERTYPE_IP);
  44         buf.arp.ar_hln = ETH_ALEN;
  45         buf.arp.ar_pln = 4; //IPPROTO_ADDR_LEN;
  46         buf.arp.ar_op = htons(ARPOP_REQUEST);
  47
  48         /* Data */
  49         memcpy(buf.ar_sha, mac, ETH_ALEN);
  50         memcpy(&buf.ar_sip, &ip, sizeof(ip));
  51         memcpy(buf.ar_tha, mac, ETH_ALEN);
  52         memcpy(&buf.ar_tip, &ip, sizeof(ip));
  53
  54         /* Now actually send the thing */
  55         fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
  56
  57         memset(&sll, 0, sizeof(sll));
  58         sll.sll_family = AF_PACKET;
  59         memcpy(sll.sll_addr, mac, sizeof(sll.sll_addr) - 1);
  60         sll.sll_halen = ETH_ALEN;
  61         sll.sll_ifindex = ifr_idx;
  62
  63         sendto(fd, &buf, sizeof(buf), 0, (struct sockaddr*)&sll, sizeof(sll));
  64         close(fd);
  65 }