#define __USE_BSD
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#define __FAVOR_BSD  /
#include <netinet/tcp.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

#define P 53


struct ipheader {
 unsigned char ip_hl:4, ip_v:4; /* this means that each member is 4 bits */
 unsigned char ip_tos;
 unsigned short int ip_len;
 unsigned short int ip_id;
 unsigned short int ip_off;
 unsigned char ip_ttl;
 unsigned char ip_p;
 unsigned short int ip_sum;
 unsigned int ip_src;
 unsigned int ip_dst;
}; /* total ip header length: 20 bytes (=160 bits) */


struct udpheader {
 unsigned short int uh_sport;
 unsigned short int uh_dport;
 unsigned short int uh_len;
 unsigned short int uh_check;
}; /* total udp header length: 8 bytes (=64 bits) */


int 
main (void)
{
  int s = socket (PF_INET, SOCK_RAW, IPPROTO_UDP);	/* open raw socket */
  char datagram[4096];	/* this buffer will contain ip header, tcp header,
			   and payload. we'll point an ip header structure
			   at its beginning, and a tcp header structure after
			   that to write the header values into it */
  struct ipheader *iph   = (struct ipheader *) datagram;
  struct udpheader *udph = (struct udpheader *) datagram + sizeof (struct ipheader);
  struct sockaddr_in sin;
			/* the sockaddr_in containing the dest. address is used
			   in sendto() to determine the datagrams path */

  sin.sin_family = AF_INET;
  sin.sin_port = htons (P);/* you byte-order >1byte header values to network
			      byte order (not needed on big endian machines) */
  sin.sin_addr.s_addr = inet_addr ("127.0.0.1");

  memset (datagram, 0, 4096);	/* zero out the buffer */

/* we'll now fill in the ip header values, see above for explanations */
  iph->ip_hl = 5;
  iph->ip_v = 4;
  iph->ip_tos = 0;
  iph->ip_len = sizeof (struct ipheader) + sizeof (struct udpheader);	/* no payload */
  iph->ip_id = htonl (54321);	/* the value doesn't matter here */
  iph->ip_off = 0;
  iph->ip_ttl = 255;
  iph->ip_p = 6;
  iph->ip_sum = 0;		/* set it to 0 before computing the actual checksum later */
  iph->ip_src = inet_addr ("1.2.3.4");/* SYN's can be blindly spoofed */
  iph->ip_dst = sin.sin_addr.s_addr;
 
/* we'll now fill in the udp header values, see above for explanations */
  udph->uh_sport=12345;
  udph->uh_dport=htons(P);
  udph->uh_len=sizeof (struct udpheader);
  udph->uh_check=111;

      if (sendto (s,		/* our socket */
		  datagram,	/* the buffer containing headers and data */
		  iph->ip_len,	/* total length of our datagram */
		  0,		/* routing flags, normally always 0 */
		  (struct sockaddr *) &sin,	/* socket addr, just like in */
		  sizeof (sin)) < 0)		/* a normal send() */
	printf ("error\n");
  
   

  return 0;
}