从客户端连接（）时没有到主机的路由

Question

我基于以下做了一个简单的TCP服务器和客户端 https://www.geeksforgeeks.org/tcp-server-client-implementation-in-c/

如果我按原样编译示例代码，我发现编译错误。 所以我对原来的代码做了一点修改。 这是服务器代码。

#include <stdio.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <ifaddrs.h>
#include <arpa/inet.h>

#define PORT 12345
#define MAX 80

/* Function designed for chat between client and server */
void func(int sockfd)
{
   char buff[MAX];
   int n;

   for (;;)
   {
      bzero(buff, MAX);

      /* read the message from client and copy it in buffer */
      read(sockfd, buff, sizeof(buff));

      /* print buffer which contains the client contents */
      printf("From client : %s\t To client : ", buff);

      bzero(buff, MAX);
      n = 0;

      /* copy server message in the buffer */
      while ((buff[n++] = getchar()) != '\n')
         ;

      /* and send that buffer to client */
      write(sockfd, buff, sizeof(buff));

      /* if msg contains "Exit" then server exit and chat ended */
      if (strncmp("exit", buff, 4) == 0)
      {
         printf("Server Exit ....\n");
         break;
      }
   }
}


int main()
{
   int sockfd, connfd, len;
   struct sockaddr_in servaddr, cli;

   struct sockaddr_in *sa;
   struct ifaddrs *ifaddr, *ifa;
   char *addr;
   int family;

   if (getifaddrs(&ifaddr) == -1)
   {
      perror("getifaddrs");
      exit(0);
   }

   for (ifa = ifaddr ; ifa != NULL ; ifa = ifa->ifa_next)
   {
      if (ifa->ifa_addr == NULL)
         continue;

      family = ifa->ifa_addr->sa_family;
      if (family == AF_INET)
      {
         sa = (struct sockaddr_in *)ifa->ifa_addr;
         addr = inet_ntoa(sa->sin_addr);
         printf("Interface : %s, Address : %s\n", ifa->ifa_name, addr);
      }
   }

   /* socket creation and verification */
   sockfd = socket(AF_INET, SOCK_STREAM, 0);
   if (sockfd == -1)
   {
      printf("socket creation failed...\n");
      exit(0);
   }
   else
   {
      printf("socket successfully created...\n");
   }

   bzero(&servaddr, sizeof(servaddr));

   /* assign IP and PORT */
   servaddr.sin_family = AF_INET;
   servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
   servaddr.sin_port = htons(PORT);

   if ((bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr))) != 0)
   {
      printf("socket bind failed...\n");
      exit(0);
   }
   else
   {
      printf("Socket successfully binded...\n");
   }

   /* Now server is ready to listen and verification */
   if ((listen(sockfd, 5)) != 0)
   {
      printf("Listen failed ...\n");
      exit(0);
   }
   else
   {
      printf("Server listening ...\n");
   }

   len = sizeof(cli);


   /* Accept the data packet from client and verification */
   connfd = accept(sockfd, (struct sockaddr *)&cli, &len);
   if (connfd < 0)
   {
      printf("Server accept failed...\n");
      exit(0);
   }
   else
   {
      printf("Server accept the client...\n");
   }

   /* Function for chatting between client and server */
   func(connfd);

   /* After chatting, close the socket */
   close(sockfd);
}

这是客户端代码。

#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>

#define MAX 80
#define PORT 12345

void func(int sockfd)
{
   char buff[MAX];
   int n;

   for (;;)
   {
      bzero(buff, sizeof(buff));
      printf("Enter the string : ");

      n = 0;
      while ((buff[n++] = getchar()) != '\n')
         ;

      write(sockfd, buff, sizeof(buff));
      bzero(buff, sizeof(buff));

      read(sockfd, buff, sizeof(buff));
      printf("From Server : %s", buff);

      if ((strncmp(buff, "exit", 4)) == 0)
      {
         printf("Client Exit ...\n");
         break;
      }
   }
}


int main()
{
   int sockfd, connfd;
   struct sockaddr_in servaddr, cli;

   /* socket create and verification */
   sockfd = socket(AF_INET, SOCK_STREAM, 0);
   if (sockfd == -1)
   {
      printf("socket creation failed...\n");
      exit(0);
   }
   else
   {
      printf("socket successfully created...\n");
   }

   bzero(&servaddr, sizeof(servaddr));

   /* assign IP, PORT */
   servaddr.sin_family = AF_INET;
   servaddr.sin_addr.s_addr = inet_addr("192.168.1.203");
   servaddr.sin_port = htons(PORT);

   /* connect the client socket to server socket */
   if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0)
   {
      printf("connection with the server failed ...[%s]\n", strerror(errno));
      exit(0);
   }
   else
   {
      printf("connected to the server ...\n");
   }

   /* function for chat */
   func(sockfd);

   /* close the socket */
   close(sockfd);
   return 0;
}

我在 192.168.1.203 上运行服务器，在 192.168.1.219 上运行客户端。 我可以在 192.168.1.203 和 192.168.1.219 之间 ping 通。 并且iptables都被清空了。 （运行 iptables -F）。

但是从客户端，我看到“没有到主机的路由”错误消息。 这是我执行服务器程序时来自服务器端的消息。

# ./server
Interface : lo, Address : 127.0.0.1
Interface : ens37, Address : 192.168.1.203
socket successfully created...
Socket successfully binded...
Server listening ...

以下是客户端发来的消息

# ./client
# ./client
socket successfully created...
connection with the server failed ...[No route to host]

如果有人指出我做错了什么，那就太好了。

Answer 1

我测试了几个想法，终于找到了原因。 当我使用“systemctl”从 CentOS8 系统停止防火墙时 停止防火墙”。 然后，一切顺利。