UDP socket 绑固定IP实验

遇到一个问题，本机IP修改之后，UDP收不到包了。走查代码发现socket绑定时填写的IP不是INADDR_ANY，而是绑成了固定IP，并且修改IP时没有重新绑socket。

为了验证这种情况，专门写了个程序验证。（只有一台linux，只能用win32写）

接受端：

// winsock.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <Winsock2.h>

int main(int argc, char* argv[])
{
    SOCKET sock1;
    WSADATA wdate;
    struct sockaddr_in localaddr;
    struct sockaddr_in destaddr;
    int count;
    int len;
    char buff[1024];
    char ip[16];

    if(WSAStartup(MAKEWORD(2,1), &wdate))
    {
        printf("error in %s:%d.\n", __FILE__, __LINE__);
        WSACleanup();
        return 1;
    }
    printf("WSA初始化成功.\n");
    memset((void*)ip, 0, sizeof(ip));
    printf("输入本机IP:");
    scanf("%s", ip);
    len = sizeof(destaddr);
    localaddr.sin_family=AF_INET;
    localaddr.sin_port=htons(27015); ///监听端口
    localaddr.sin_addr.s_addr=inet_addr(ip); ///注意!此处绑定固定IP

    sock1 = socket(AF_INET, SOCK_DGRAM, 0);
    bind(sock1, (struct sockaddr *)&localaddr, sizeof(localaddr));
    count = 0;
    printf("waiting dgram....\n");
    while(1)
    {
        memset((void *)buff, 0, sizeof(buff));
        if(recvfrom(sock1, buff, sizeof(buff), 0, (struct sockaddr*)&destaddr, &len) == SOCKET_ERROR)
        {
            printf("error in %s:%d.\n", __FILE__, __LINE__);
            closesocket(sock1);
            WSACleanup();
            return 1;
        }
        count++;
        printf("recv from%s:%s\n", inet_ntoa(destaddr.sin_addr), buff);

        if(count > 100)
            break;
    }
    closesocket(sock1);
    WSACleanup();
    return 0;
}

发送端：

 

// winsocksender.cpp : Defines the entry point for the console application.

//



#include "stdafx.h"

#include



int main(int argc, char* argv[])

{

SOCKET sock1;

WSADATA wdate;

struct sockaddr_in localaddr;

struct sockaddr_in destaddr;

int count;

int len;

char ip[16];

char buff[1024];



if(WSAStartup(MAKEWORD(2,1), &wdate))

{

printf("error in %s:%d.\n", __FILE__, __LINE__);

WSACleanup();

return 1;

}

printf("WSA初始化成功.\n");

printf("输入对端主机IP:");

scanf("%s", ip);

len = sizeof(destaddr);

destaddr.sin_family=AF_INET;

destaddr.sin_port=htons(27015); ///对端监听端口

destaddr.sin_addr.s_addr=inet_addr(ip); ///对端IP



sock1 = socket(AF_INET, SOCK_DGRAM, 0);

//bind(sock1, (struct sockaddr *)&localaddr, sizeof(localaddr));

count = 1;

printf("start sending dgram....\n", count);

while(1)

{

memset((void *)buff, 0, sizeof(buff));

sprintf(buff, "dgram %d from sender.\n", count);

if(sendto(sock1, buff, sizeof(buff), 0, (struct sockaddr*)&destaddr, len) == SOCKET_ERROR)

{

printf("error in %s:%d.\n", __FILE__, __LINE__);

closesocket(sock1);

WSACleanup();

return 1;

}

printf("dgram %d have sent.\n", count);

Sleep(10000);

count++;

if(count > 100)

break;

}

closesocket(sock1);

WSACleanup();

return 0;

}

实验：

1、打开接收端，输入本机IP，等待收包。

2、打开发送端，输入目的IP，开始发送。

此时接收端可以正常收包。

3、修改接收端 IP地址。

4、重启发送端，输入新的目的IP地址，开始发送。

此时接收端不能收包。

5、重启接收端，输入新IP，等待收包。

此时接受正常。