Linux下TCP通信在两个虚拟机上连接失败
情况描述:
在一台虚拟机上使用回环地址(127.0.0.1)时一切正常,当部署到两台虚拟机(局域网下同网段)上时出现连接失败的情况。
解决办法:
首先使用命令nc -z -v <ip地址> <端口号>测试TCP端口是否能连通(UDP也可使用nc命令,具体请百度),若出现下面结果则正确:
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 10.203.181.153:9118.
Ncat: 0 bytes sent, 0 bytes received in 0.02 seconds
若失败,请尝试关闭虚拟机的防火墙,相关命令如下:
sudo systemctl disable firewalld.service(开机自动关闭防火墙)
sudo systemctl stop firewalld.service(关闭防火墙)
关闭防火墙后,先后运行服务端代码以及客户端代码,即可成功连接!
TCP客户端程序如下:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
int main(int argc, char *argv[])
{
int sock;
char message[BUF_SIZE];
int str_len, recv_len, recv_cnt;
struct sockaddr_in serv_adr;
if(argc!=3) {
printf("Usage : %s <IP> <port>\n", argv[0]);
exit(1);
}
sock=socket(PF_INET, SOCK_STREAM, 0);
if(sock==-1)
error_handling("socket() error");
memset(&serv_adr, 0, sizeof(serv_adr));
serv_adr.sin_family=AF_INET;
serv_adr.sin_addr.s_addr=inet_addr(argv[1]);
serv_adr.sin_port=htons(atoi(argv[2]));
if(connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
error_handling("connect() error!");
else
puts("Connected...........");
while(1)
{
fputs("Input message(Q to quit): ", stdout);
fgets(message, BUF_SIZE, stdin);
if(!strcmp(message,"q\n") || !strcmp(message,"Q\n"))
break;
str_len=write(sock, message, strlen(message));
recv_len=0;
while(recv_len<str_len)
{
recv_cnt=read(sock, &message[recv_len], BUF_SIZE-1);
if(recv_cnt==-1)
error_handling("read() error!");
recv_len+=recv_cnt;
}
message[recv_len]=0;
printf("Message from server: %s", message);
}
close(sock);
return 0;
}
void error_handling(char *message)
{
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}
TCP服务端程序如下:
// An highlighted block
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
void error_handling(char *message);
int main(int argc, char *argv[])
{
int serv_sock, clnt_sock;
char message[BUF_SIZE];
int str_len, i;
struct sockaddr_in serv_adr;
struct sockaddr_in clnt_adr;
socklen_t clnt_adr_sz;
if(argc!=2) {
printf("Usage : %s <port>\n", argv[0]);
exit(1);
}
serv_sock=socket(PF_INET, SOCK_STREAM, 0);
if(serv_sock==-1)
error_handling("socket() error");
memset(&serv_adr, 0, sizeof(serv_adr));
serv_adr.sin_family=AF_INET;
serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
serv_adr.sin_port=htons(atoi(argv[1]));
if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
error_handling("bind() error");
if(listen(serv_sock, 5)==-1)
error_handling("listen() error");
clnt_adr_sz=sizeof(clnt_adr);
for(i=0; i<5; i++)
{
clnt_sock=accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);
if(clnt_sock==-1)
error_handling("accept() error");
else
printf("Connected client %d \n", i+1);
while((str_len=read(clnt_sock, message, BUF_SIZE))!=0)
write(clnt_sock, message, str_len);
close(clnt_sock);
}
close(serv_sock);
return 0;
}
void error_handling(char *message)
{
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}