Send a raw Ethernet frame in Linux

sendRawEth.c

/*
 *  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;
}

Is it possible to run the src and destination to the same PC mac address?

what about crc checksum after the payload?

Is IPPROTO_RAW a valid option for AF_PACKET SOCK_RAW socket? However it doesn't matter for sending raw ethernet packet:)

By using raw sockets is it possible full duplex communication of Ethernet frames

If your Ethernet controller is in Full Duplex mode then it will always do so regardless, if it's in Half Duplex then no

Thanks for sharing. It helped a lot.