ping using tcp ip

Server.c

#include <unistd.h>

#include <stdio.h>

#include <sys/socket.h>

#include <netinet/ip.h>

#include <netinet/tcp.h>

// Packet length

#define PCKT_LEN 8192

 // May create separate header file (.h) for all

 // headers' structures

 // IP header's structure

struct ipheader {

 unsigned char      iph_ihl:5,

                    iph_ver:4;

 unsigned char      iph_tos;

 unsigned short int iph_len;

 unsigned short int iph_ident;

 unsigned char      iph_flags;

 unsigned short int iph_offset;

 unsigned char      iph_ttl;

 unsigned char      iph_protocol;

 unsigned short int iph_chksum;

 unsigned int       iph_sourceip;

 unsigned int       iph_destip;

};

/* Structure of a TCP header */

struct tcpheader {

 unsigned short int tcph_srcport;

 unsigned short int tcph_destport;

 unsigned int       tcph_seqnum;

 unsigned int       tcph_acknum;

 unsigned char      tcph_reserved:4, tcph_offset:4;

 // unsigned char tcph_flags;

  unsigned int

       tcp_res1:4,       /*little-endian*/

       tcph_hlen:4,      /*length of tcp header in 32-bit words*/

       tcph_fin:1,       /*Finish flag "fin"*/

       tcph_syn:1,       /*Synchronize sequence numbers to start a connection*/

       tcph_rst:1,       /*Reset flag */

       tcph_psh:1,       /*Push, sends data to the application*/

       tcph_ack:1,       /*acknowledge*/

       tcph_urg:1,       /*urgent pointer*/

       tcph_res2:2;

 unsigned short int tcph_win;

 unsigned short int tcph_chksum;

 unsigned short int tcph_urgptr;

};

// Simple checksum function, may use others such as Cyclic Redundancy Check, CRC

unsigned short csum(unsigned short *buf, int len)

{

        unsigned long sum;

        for(sum=0; len>0; len--)

                sum += *buf++;

        sum = (sum >> 16) + (sum &0xffff);

        sum += (sum >> 16);

        return (unsigned short)(~sum);

}

int main(int argc, char *argv[])

{

int sd;

// No data, just datagram

char buffer[PCKT_LEN];

// The size of the headers

struct ipheader *ip = (struct ipheader *) buffer;

struct tcpheader *tcp = (struct tcpheader *) (buffer + sizeof(struct ipheader));

struct sockaddr_in sin, din;

int one = 1;

const int *val = &one;

memset(buffer, 0, PCKT_LEN);

if(argc != 5)

{

printf("- Invalid parameters!!!\n");

printf("- Usage: %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);

exit(-1);

}

sd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);

if(sd < 0)

{

   perror("socket() error");

   exit(-1);

}

else

printf("socket()-SOCK_RAW and tcp protocol is OK.\n");

// The source is redundant, may be used later if needed

// Address family

sin.sin_family = AF_INET;

din.sin_family = AF_INET;

// Source port, can be any, modify as needed

sin.sin_port = htons(atoi(argv[2]));

din.sin_port = htons(atoi(argv[4]));

// Source IP, can be any, modify as needed

sin.sin_addr.s_addr = inet_addr(argv[1]);

din.sin_addr.s_addr = inet_addr(argv[3]);

// IP structure

ip->iph_ihl = 5;

ip->iph_ver = 4;

ip->iph_tos = 16;

ip->iph_len = sizeof(struct ipheader) + sizeof(struct tcpheader);

ip->iph_ident = htons(54321);

ip->iph_offset = 0;

ip->iph_ttl = 64;

ip->iph_protocol = 6; // TCP

ip->iph_chksum = 0; // Done by kernel

// Source IP, modify as needed, spoofed, we accept through command line argument

ip->iph_sourceip = inet_addr(argv[1]);

// Destination IP, modify as needed, but here we accept through command line argument

ip->iph_destip = inet_addr(argv[3]);

// The TCP structure. The source port, spoofed, we accept through the command line

tcp->tcph_srcport = htons(atoi(argv[2]));

// The destination port, we accept through command line

tcp->tcph_destport = htons(atoi(argv[4]));

tcp->tcph_seqnum = htonl(1);

tcp->tcph_acknum = 0;

tcp->tcph_offset = 5;

tcp->tcph_syn = 1;

tcp->tcph_ack = 0;

tcp->tcph_win = htons(32767);

tcp->tcph_chksum = 0; // Done by kernel

tcp->tcph_urgptr = 0;

// IP checksum calculation

ip->iph_chksum = csum((unsigned short *) buffer, (sizeof(struct ipheader) + sizeof(struct tcpheader)));

// Inform the kernel do not fill up the headers' structure, we fabricated our own

if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0)

{

    perror("setsockopt() error");

    exit(-1);

}

else

   printf("setsockopt() is OK\n");

printf("Using:::::Source IP: %s port: %u, Target IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));

// sendto() loop, send every 2 second for 50 counts

unsigned int count;

for(count = 0; count < 20; count++)

{

if(sendto(sd, buffer, ip->iph_len, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0)

// Verify

{

   perror("sendto() error");

   exit(-1);

}

else

   printf("Count #%u - sendto() is OK\n", count);

sleep(2);

}

close(sd);

return();
}