Send a raw Ethernet frame in Linux

sendRawEth.c

/*
 * Added the command line arguments for interface and MAC Address
 * 
 * Based on raw Ethernet from austinmarton: https://gist.github.com/1922600
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 */

#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>

#define DEFAULT_IF "eth0"
#define BUF_SIZ 1024

int main(int argc, char *argv[])
{
int sockfd;
struct ifreq if_idx;
struct ifreq if_mac;
int tx_len = 0;
char sendbuf[BUF_SIZ];
struct ether_header *eh = (struct ether_header *) sendbuf;
struct iphdr *iph = (struct iphdr *) (sendbuf + sizeof(struct ether_header));
struct sockaddr_ll socket_address;
char ifName[IFNAMSIZ];
unsigned int mac[6]; //using as uint8_t

/* Get interface name */
if (argc > 1){
  strcpy(ifName, argv[1]);
    if (argc > 2) { /* 2 arguments, second argument is mac */
      sscanf(argv[2], "%02x:%02x:%02x:%02x:%02x:%02x", &mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]);
      //printf("mac:\n");
      //printf("%2x:%2x:%2x:%2x:%2x:%2x\n", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
    }
}
else
strcpy(ifName, DEFAULT_IF);

/* Open RAW socket to send on */
if ((sockfd = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW)) == -1) {
perror("socket");
}

/* Get the index of the interface to send on */
memset(&if_idx, 0, sizeof(struct ifreq));
strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0)
perror("SIOCGIFINDEX");
/* Get the MAC address of the interface to send on */
memset(&if_mac, 0, sizeof(struct ifreq));
strncpy(if_mac.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0)
perror("SIOCGIFHWADDR");

/* Construct the Ethernet header */
memset(sendbuf, 0, BUF_SIZ);
/* Ethernet header */
eh->ether_shost[0] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[0];
eh->ether_shost[1] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[1];
eh->ether_shost[2] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[2];
eh->ether_shost[3] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[3];
eh->ether_shost[4] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[4];
eh->ether_shost[5] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[5];
eh->ether_dhost[0] = mac[0];
eh->ether_dhost[1] = mac[1];
eh->ether_dhost[2] = mac[2];
eh->ether_dhost[3] = mac[3];
eh->ether_dhost[4] = mac[4];
eh->ether_dhost[5] = mac[5];
/* Ethertype field */
eh->ether_type = htons(ETH_P_IP);
tx_len += sizeof(struct ether_header);

/* Packet data */
sendbuf[tx_len++] = 0xde;
sendbuf[tx_len++] = 0xad;
sendbuf[tx_len++] = 0xbe;
sendbuf[tx_len++] = 0xef;

/* Index of the network device */
socket_address.sll_ifindex = if_idx.ifr_ifindex;
/* Address length*/
socket_address.sll_halen = ETH_ALEN;
/* Destination MAC */
socket_address.sll_addr[0] = mac[0];
socket_address.sll_addr[1] = mac[1];
socket_address.sll_addr[2] = mac[2];
socket_address.sll_addr[3] = mac[3];
socket_address.sll_addr[4] = mac[4];
socket_address.sll_addr[5] = mac[5];

/* Send packet */
if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
printf("Send failed\n");

return 0;
}