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#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#define HEX_PER_COLUMN 16
#define MAX_PACKET_SIZE 100
#define IPHDR_ID 0x1234
#define IPHDR_TTL 100
#define IPHDR_SOURCE "192.168.1.2"
#define IPHDR_DESTINATION "192.168.1.254"
#define ICMPHDR_ID 0x5678
#define ICMPHDR_SEQUENCE 1
#define MAX_BUFFER 1000
char * createPing(int * length);
void computeICMPChecksum(char * packet, int length);
void computeIPChecksum(char * packet, int length);
void computeChecksums(char * packet, int length);
void displayPacket(char *, int length);
short checksum(char * buffer, short length);
int main(void) {
char * packet;
int length;
int s;
int s2;
char buffer[MAX_BUFFER];
int i;
struct sockaddr_in from;
// creates packet
packet = createPing(&length);
displayPacket(packet, length);
computeChecksums(packet, length);
displayPacket(packet, length);
// creates socket
s = socket(PF_INET, SOCK_RAW, IPPROTO_RAW);
if (s<0) {
perror("socket");
}
s2 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
if (s2<0) {
perror("socket (s2)");
}
// sends packet
struct sockaddr_in destination;
destination.sin_family = AF_INET;
destination.sin_port = htons(0);
destination.sin_addr.s_addr = inet_addr(IPHDR_DESTINATION);
for (i=0; i<8; i++) {
destination.sin_zero[i] = 0;
}
int hincl = 1;
if(setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl)) < 0)
{
perror("Setsockopt error");
printf("Errno = %d",errno);
}
if (sendto(s, packet, length, 0, (struct sockaddr *)&destination, sizeof(struct sockaddr_in))<0) {
perror("send");
}
// wait for packet
while (1) {
length = recvfrom(s2, buffer, MAX_BUFFER, 0, (struct sockaddr *)&from, &i);
packet = inet_ntoa(from.sin_addr);
printf("recv from %s, length=%d\n", packet, length);
if (length<0) {
perror("recvfrom");
exit(EXIT_FAILURE);
}
displayPacket(buffer, length);
}
close(s);
close(s2);
free(packet);
}
char * createPing(int * length) {
char * packet;
struct ip * ipHeader;
struct icmp * icmpHeader;
packet = (char *)malloc(MAX_PACKET_SIZE*sizeof(char));
*length = sizeof(struct ip)+sizeof(struct icmp);
// IP header
ipHeader = (struct ip *)packet;
ipHeader->ip_hl = sizeof(struct ip)/4;
ipHeader->ip_v = 4;
ipHeader->ip_tos = 0;
ipHeader->ip_len = htons(sizeof(struct ip)+sizeof(struct icmp));
ipHeader->ip_id = htons(IPHDR_ID);
ipHeader->ip_off = htons(0);
ipHeader->ip_ttl = IPHDR_TTL;
ipHeader->ip_p = IPPROTO_ICMP;
ipHeader->ip_sum = htons(0);
inet_aton(IPHDR_SOURCE,&ipHeader->ip_src);
inet_aton(IPHDR_DESTINATION,&ipHeader->ip_dst);
// ICMP header
icmpHeader = (struct icmp *)(packet+sizeof(struct ip));
icmpHeader->icmp_type = ICMP_ECHO;
icmpHeader->icmp_code = 0;
icmpHeader->icmp_cksum = htons(0);
icmpHeader->icmp_hun.ih_idseq.icd_id = htons(ICMPHDR_ID);
icmpHeader->icmp_hun.ih_idseq.icd_seq = htons(ICMPHDR_SEQUENCE);
return packet;
}
void displayPacket(char * packet, int length) {
int i, j;
for (i=0; i<(length+HEX_PER_COLUMN-1)/HEX_PER_COLUMN; i++) {
j = 0;
while ((j<HEX_PER_COLUMN) && (HEX_PER_COLUMN*i+j<length)) {
printf("%02x ", (unsigned char)packet[HEX_PER_COLUMN*i+j]);
j = j+1;
}
printf("\n");
}
}
void computeChecksums(char * packet, int length) {
computeICMPChecksum(packet, length);
computeIPChecksum(packet, length);
}
void computeIPChecksum(char * packet, int length) {
struct ip * ipHeader;
ipHeader = (struct ip *)packet;
ipHeader->ip_sum = htons(checksum((char *)ipHeader, length));
}
void computeICMPChecksum(char * packet, int length) {
struct icmp * icmpHeader;
icmpHeader = (struct icmp *)(packet+sizeof(struct ip));
icmpHeader->icmp_cksum = htons(checksum((char *)icmpHeader, length-sizeof(struct ip)));
}
short checksum(char * buffer, short length) {
short word;
int sum = 0;
int i = 0;
while (i<length) {
if (i+1<length) {
word = 256*buffer[i]+buffer[i+1];
}
else {
word = 256*buffer[i];
}
sum = sum+word;
i = i+2;
}
while ((sum>>16)!=0) {
sum = (sum&0xFFFF)+(sum>>16);
}
sum = ~sum;
word = (short)sum;
return word;
} |
