header 1st

the headers...

4juneraw.h (headders.h)

#include<stdio.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/udp.h>




//the ip header structure
struct iphdrr
{
 unsigned char iph_ihl:5;
 unsigned char iph_ver:4;
 unsigned char      iph_tos;
 unsigned short int iph_len;
 unsigned short int iph_ident;
 unsigned char      iph_flag;
 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;
 
};

//tcp header structure

struct tcphdr
{
 unsigned short int th_sport;
 unsigned short int th_dport;
 unsigned int th_seq;
 unsigned int th_ack;
 unsigned char th_x2:4, th_off:4;
 unsigned char th_flags;
 unsigned short int th_win;
 unsigned short int th_sum;
 unsigned short int th_urp;
 
};




// UDP header's structure

struct udpheader {

  unsigned short int udph_srcport;
  unsigned short int udph_destport;
  unsigned short int udph_len;
  unsigned short int udph_chksum;

};

//icmp header structure

struct icmpheader {
 unsigned char icmp_type;
 unsigned char icmp_code;
 unsigned short int icmp_cksum;
/* The following data structures are ICMP type specific */
 unsigned short int icmp_id;
 unsigned short int icmp_seq;
};

//function to calculate generic checksum

/*unsigned short csum(unsigned short *buf, int nwords)

{      
        unsigned long sum;

        for(sum=0; nwords>0; nwords--)
    sum += *buf++;
    sum = (sum >> 16) + (sum &0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);

}
*/