----send_tcp.c----
#include <stdio.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib,"ws2_32")

typedef struct ip_header {
        unsigned char ip_verlen;        // IP version & length
        unsigned char ip_tos;           // IP type of service
        unsigned short ip_totallength;   // Total length
        unsigned short ip_id;            // Unique identifier 
        unsigned short ip_offset;        // Fragment offset field
        unsigned char ip_ttl;           // Time to live
        unsigned char ip_protocol;      // Protocol(TCP,UDP etc)
        unsigned short ip_sum;          // IP checksum
        unsigned int ip_srcaddr;       // Source address
        unsigned int ip_destaddr;      // Destination address
} IPHDR;

typedef struct tcp_header {
        unsigned short int tcp_sport; //
        unsigned short int tcp_dport; //
        unsigned int tcp_seq; //
        unsigned int tcp_ack;
        unsigned char tcp_x2:4, th_off:4;
        unsigned char tcp_flags;
        unsigned short int tcp_win;
        unsigned short int tcp_sum;
        unsigned short int tcp_urp;
} TCPHDR; 

#define FROM_IP "127.0.0.1"
#define TO_IP "127.0.0.1"

// подсчет чексуммы взял из статьи "Программирование raw сокетов под bsd", xaoc ezine #1
USHORT checksum(USHORT *buffer, int size)
{
    unsigned long cksum=0;

    while (size > 1)
    {
        cksum += *buffer++;
        size  -= sizeof(USHORT);   
    }
    if (size)
    {
        cksum +=(UCHARbuffer;   
    }
    cksum = (cksum >> 16) + (cksum & 0xffff);
    cksum += (cksum >>16); 

    return (USHORT)(~cksum); 
}

void main() {
	WSADATA wd;
	SOCKET s;
	IN_ADDR addr;
	int optret,ret;
	BOOL bopt;
	IPHDR iphdr;
	TCPHDR tcphdr;
	unsigned short tsz,tcpsum,chksum;
	char buf[4096], *ptr;
	struct sockaddr_in s_in;

	if (WSAStartup(MAKEWORD(2,2),&wd))
		printf("WSAStartup() failed\n");
	
	addr.S_un.S_addr = inet_addr(FROM_IP);

	s = socket(AF_INET,SOCK_RAW,IPPROTO_TCP);
	if (s == INVALID_SOCKET)
		printf("socket() failed\n");

	bopt = TRUE;
	optret = setsockopt(s,IPPROTO_IP,IP_HDRINCL,(char *)&bopt,sizeof(bopt));
	if (optret == SOCKET_ERROR)
		printf("setsockopt() failed\n");

	tsz = sizeof(IPHDR) + sizeof(TCPHDR);

	iphdr.ip_verlen = (4 << 4) | (sizeof(iphdr) / sizeof(unsigned long));
	iphdr.ip_tos =  0;
	iphdr.ip_totallength = htons(tsz);
	iphdr.ip_id = 0;
	iphdr.ip_offset = 0;
	iphdr.ip_ttl = 128;
	iphdr.ip_protocol = 0x06;
	iphdr.ip_sum = 0;
	iphdr.ip_srcaddr = inet_addr(FROM_IP);
	iphdr.ip_destaddr = inet_addr(TO_IP);

	tcphdr.tcp_sport = htons(666);
	tcphdr.tcp_dport = htons(999);
	tcphdr.tcp_seq = 555;
	tcphdr.tcp_ack = 777;
	tcphdr.tcp_flags = 0x10; // ACK
	tcphdr.tcp_win = htons(6666);

	ptr = buf;
	ZeroMemory(buf,sizeof(buf));
	tcpsum = 0;

	memcpy(ptr,&iphdr.ip_srcaddr,sizeof(iphdr.ip_srcaddr));
	ptr += sizeof(iphdr.ip_srcaddr);
	tcpsum += sizeof(iphdr.ip_srcaddr);

	memcpy(ptr,&iphdr.ip_destaddr,sizeof(iphdr.ip_destaddr));
	ptr += sizeof(iphdr.ip_destaddr);
	tcpsum += sizeof(iphdr.ip_destaddr);

	memcpy(ptr,&iphdr.ip_destaddr,sizeof(iphdr.ip_destaddr));
	ptr += sizeof(iphdr.ip_destaddr);
	tcpsum += sizeof(iphdr.ip_destaddr);

	ptr++;
	tcpsum++;

	memcpy(ptr,&iphdr.ip_protocol,sizeof(iphdr.ip_protocol));
	ptr += sizeof(iphdr.ip_protocol);
	tcpsum += sizeof(iphdr.ip_protocol);

	memcpy(ptr,&tcphdr,sizeof(tcphdr));
	ptr += sizeof(tcphdr);
	tcpsum += sizeof(tcphdr);

        tcphdr.tcp_sum = checksum((USHORT *)&buf,tcpsum);

	ZeroMemory(buf,4096);
	ptr = buf;
	
	memcpy(ptr,&iphdr,sizeof(iphdr));
	ptr += sizeof(iphdr);
	memcpy(ptr,&tcphdr,sizeof(tcphdr));

	s_in.sin_family = AF_INET;
	s_in.sin_port = htons(666);
	s_in.sin_addr.s_addr = inet_addr(TO_IP);

	ret = sendto(s,&buf,tsz,0,(struct sockaddr *)&s_in,sizeof(s_in));

	if (ret == SOCKET_ERROR)
		printf("sendto() failed: %d\n",WSAGetLastError());

}
------eof-------