Sending raw Ethernet packets from a specific interface in C on Linux

Lately austinmarton’ve been writing some code to send packets to a specific MAC address from a specific interface. He is sure this will come in handy again so here is how it goes:

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Source :

/*
	* 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 MY_DEST_MAC0 0x00
	#define MY_DEST_MAC1 0x00
	#define MY_DEST_MAC2 0x00
	#define MY_DEST_MAC3 0x00
	#define MY_DEST_MAC4 0x00
	#define MY_DEST_MAC5 0x00
	#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];
	/* Get interface name */
	if (argc > 1)
	strcpy(ifName, argv[1]);
	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] = MY_DEST_MAC0;
	eh->ether_dhost[1] = MY_DEST_MAC1;
	eh->ether_dhost[2] = MY_DEST_MAC2;
	eh->ether_dhost[3] = MY_DEST_MAC3;
	eh->ether_dhost[4] = MY_DEST_MAC4;
	eh->ether_dhost[5] = MY_DEST_MAC5;
	/* 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] = MY_DEST_MAC0;
	socket_address.sll_addr[1] = MY_DEST_MAC1;
	socket_address.sll_addr[2] = MY_DEST_MAC2;
	socket_address.sll_addr[3] = MY_DEST_MAC3;
	socket_address.sll_addr[4] = MY_DEST_MAC4;
	socket_address.sll_addr[5] = MY_DEST_MAC5;
	/* Send packet */
	if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
	printf("Send failed\n");
	return 0;
	}