请教TCP通信的问题

没做过
是不是要直接修改C1发送过来的ip包？把ip地址改成c的？

长连接是建立来发送是不行的！自己按TCP的格式组IP包，发给主站！

对于S来说，它已经建立了C连接了，即它会接收C的MAC地址和端口发送过来的数据，如果你想C1发送的数据S能接收，你就要把C1的端口改为C的端口，用raw来做可能能实现。
就有如是sniffer pro的修改数据发送

向ydzqw(===七条狗===)(@@我不爱做菜) 学习

谢谢各位特别是ydzqw(===七条狗===)(@@我不爱做菜)
我试试
大家请不吝指教

在tcp/ip协议下目标ip＋目标端口源ip+源端口都可以自己设定
这个用raw_socket就可以实现
我写了 s c c1 三个程序了
不过c1却不能按预期的方式工作比较郁闷
贴出来大家一起帮我搞定一下3个程序都是在linux下实现的其中运行c1需要有root权限(raw_socket只有root权限用户才能创建）3个程序是这个工作的：服务进程S：
运行服务进程有一个参数：服务端口
假设服务端口为8000 则这样运行： ./s 8000
程序运行后，如果有客户进程连接，服务器会提示该客户进程的地址和端口
服务进程接收来自客户端的一个字符串并给该客户一个确认消息。客户进程C:
客户进程有2个参数：服务器地址服务器端口
调试时候服务进程S和客户进程C都在自己机上所以可以这样运行 ./c localhost 8000
程序运行后，会等待用户输入一个字符串发送到服务器，同时接收到服务器的确认消息。伪装进程c1:
伪装进程没有命令行参数，不过运行时候我提示了：cin severport and clientport
severport就是s的端口 clientport为要伪装的客户进程C的端口(c的端口在c运行后在s中有提示，程序里面c1把源地址和目标地址都设为localhost了），我希望c1运行后服务进程S能发一个消息到客户进程c，但是没有成功。下面是3个程序：

/******* 服务器程序 (server.c) ************/
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>#define EXIT 100int main(int argc, char *argv[])
{
int sockfd,new_fd;
struct sockaddr_in server_addr;
struct sockaddr_in client_addr;
int sin_size,portnumber;
char hello[]="Get!!!\n";
char buffer[1024];
int nbytes;if(argc!=2)
{
fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]);
exit(1);
} if((portnumber=atoi(argv[1]))<0)
{
fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]);
exit(1);
} /* 服务器端开始建立socket描述符 */
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
fprintf(stderr,"Socket error:%s\n\a",strerror(errno));
exit(1);
} /* 服务器端填充 sockaddr结构 */
bzero(&server_addr,sizeof(struct sockaddr_in));
server_addr.sin_family=AF_INET;
server_addr.sin_addr.s_addr=htonl(INADDR_ANY);
server_addr.sin_port=htons(portnumber); /* 捆绑sockfd描述符 */
if(bind(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
{
fprintf(stderr,"Bind error:%s\n\a",strerror(errno));
exit(1);
} /* 监听sockfd描述符 */
if(listen(sockfd,10)==-1)
{
fprintf(stderr,"Listen error:%s\n\a",strerror(errno));
exit(1);
} while(1)
{
    /* 服务器阻塞,直到客户程序建立连接 */
    sin_size=sizeof(struct sockaddr_in);
    if((new_fd=accept(sockfd,(struct sockaddr *)(&client_addr),&sin_size))==-1)
    {
        fprintf(stderr,"Accept error:%s\n\a",strerror(errno));
        exit(1);
    }     /* 建立一个子进程和客户进程连接 */
    if(fork()==0)
    {
        fprintf(stderr,"Server get connection from %s:%d\n", inet_ntoa(client_addr.sin_addr),
ntohs(client_addr.sin_port));
        while(1)
{
if((nbytes=read(new_fd,buffer,1024))==-1)
        {
                fprintf(stderr,"Read Error:%s\n",strerror(errno));
                exit(1);
        }
buffer[nbytes]='\0';
if(strcmp(buffer,"exit")==0)
{
close(new_fd);
exit(EXIT);
}
        fprintf(stderr,"get message from cilent:%s\n",buffer);

if(write(new_fd,hello,strlen(hello))==-1)
{
                fprintf(stderr,"Write Error:%s\n",strerror(errno));
                exit(1);
        }
}

    }
}
close(sockfd);
exit(0);
}

/******* 客户端程序 client.c ************/
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>#define EXIT 100int main(int argc, char *argv[])
{
int sockfd;
char buffer[1024];
struct sockaddr_in server_addr;
struct hostent *host;
int portnumber,nbytes; int exitstatus;if(argc!=3)
{
fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]);
exit(1);
} if((host=gethostbyname(argv[1]))==NULL)
{
fprintf(stderr,"Gethostname error\n");
exit(1);
} if((portnumber=atoi(argv[2]))<0)
{
fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]);
exit(1);
} /* 客户程序开始建立 sockfd描述符 */
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
fprintf(stderr,"Socket Error:%s\a\n",strerror(errno));
exit(1);
} /* 客户程序填充服务端的资料 */
bzero(&server_addr,sizeof(server_addr));
server_addr.sin_family=AF_INET;
server_addr.sin_port=htons(portnumber);
server_addr.sin_addr=*((struct in_addr *)host->h_addr); /* 客户程序发起连接请求 */
if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
{
fprintf(stderr,"Connect Error:%s\a\n",strerror(errno));
exit(1);
}
/* 连接成功了 */
/* 创建一个子进程往服务器发送数据 */
if(fork()==0)
{
while(1)
{
/* getline(buffer); */
scanf("%s",buffer);
if(write(sockfd,buffer,strlen(buffer))==-1)
{
    fprintf(stderr,"Write Error:%s\n",strerror(errno));
    exit(1);
}
if(strcmp(buffer,"exit")==0)
{
close(sockfd);
exit(EXIT);
}
}
}
/* 创建一干子进程接收并显示服务器来的数据 */
if(fork()==0)
{
while(1)
{

if((nbytes=read(sockfd,buffer,1024))==-1)
{
fprintf(stderr,"Read Error:%s\n",strerror(errno));
exit(1);
}
buffer[nbytes]='\0';
printf("Get Message from server:%s",buffer);
}
}
while(1)
{
wait(&exitstatus);
exitstatus=(exitstatus>>8)%256;
if(exitstatus==EXIT)
exit(0);
}}

/****************** c1.c **********************/
#define __USE_BSD /* use bsd'ish ip header */
#include <sys/socket.h> /* these headers are for a Linux system, but */
#include <netinet/in.h> /* the names on other systems are easy to guess.. */
#include <netinet/ip.h>
#define __FAVOR_BSD /* use bsd'ish tcp header */
#include <netinet/tcp.h>
#include <unistd.h>int serverport,clientport;
char message[]="cloud_long";
unsigned short /* this function generates header checksums */
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 ~sum;
}int
main (void)
{
  int s = socket (PF_INET, SOCK_RAW, IPPROTO_TCP); /* 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 ip *iph = (struct ip *) datagram;
  struct tcphdr *tcph = (struct tcphdr *) datagram + sizeof (struct ip);
  struct sockaddr_in sin;
/* the sockaddr_in containing the dest. address is used
   in sendto() to determine the datagrams path */
printf("cin serverport and client:");
scanf("%d%d",&serverport,&clientport);  sin.sin_family = AF_INET;
  sin.sin_port = htons (serverport);/* 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 */  strcpy(datagram+sizeof(struct ip)+sizeof(struct tcphdr),message);/* we'll now fill in the ip/tcp header values, see above for explanations */
  iph->ip_hl = 5;
  iph->ip_v = 4;
  iph->ip_tos = 0;
  iph->ip_len = sizeof (struct ip) + sizeof (struct tcphdr) + strlen (message);
  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.s_addr = inet_addr ("127.0.0.1");/* SYN's can be blindly spoofed */
  iph->ip_dst.s_addr = sin.sin_addr.s_addr;
  tcph->th_sport = htons (clientport); /* arbitrary port */
  tcph->th_dport = htons (serverport);
  tcph->th_seq = random ();/* in a SYN packet, the sequence is a random */
  tcph->th_ack = 0;/* number, and the ack sequence is 0 in the 1st packet */
  tcph->th_x2 = 0;
  tcph->th_off = 0; /* first and only tcp segment */
  tcph->th_flags = TH_SYN; /* initial connection request */
  tcph->th_win = htonl (65535); /* maximum allowed window size */
  tcph->th_sum = 0;/* if you set a checksum to zero, your kernel's IP stack
      should fill in the correct checksum during transmission */
  tcph->th_urp = 0;  iph->ip_sum = csum ((unsigned short *) datagram, iph->ip_len >> 1);

/* finally, it is very advisable to do a IP_HDRINCL call, to make sure
   that the kernel knows the header is included in the data, and doesn't
   insert its own header into the packet before our data */  { /* lets do it the ugly way.. */
    int one = 1;
    const int *val = &one;
    if (setsockopt (s, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)
      printf ("Warning: Cannot set HDRINCL!\n");
  }

      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;
}

调试易

请教TCP通信的问题

解决方案 »