關於雙網卡同網段的廣播問題

假設有電腦A和電腦B，A雙網卡並且雙網卡的IP是同一網段，並且A的網段和B的網段在同一網段，現在B進行廣播，我們會看到A收到了兩次信息，程序如下：

//server.cpp
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <string.h>

char * host_name = "192.168.0.255";
int port = 10051;

int main(void)
{
struct sockaddr_in serv_addr,addr;
char buf[256];

int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == -1)
{
perror("Error: socket";
return -1;
}
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = inet_addr(host_name);//htonl(INADDR_ANY);//

int bd = bind(sockfd, (struct sockaddr*)&addr, sizeof(struct sockaddr_in));
while(1)
{
int len = sizeof(serv_addr);
memset(&serv_addr, 0, len);
int ret = recvfrom(sockfd,buf,sizeof(buf),0,(struct sockaddr*)&serv_addr,(socklen_t*)&len);
printf("recv=%d buf=%s
",ret, buf);
printf("RecvieIPs Recive Portd
", inet_ntoa(serv_addr.sin_addr),
ntohs(serv_addr.sin_port));
ret = sendto(sockfd,buf,sizeof(buf),0,(struct sockaddr*)&serv_addr,sizeof(struct sockaddr_in));
}

}


//client.cpp

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

char * host_name = "192.168.0.255";

int port = 10051;
int main(void)
{
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == -1)
{
perror("Error: socket";
return -1;
}

struct sockaddr_in serv_addr;
memset(&serv_addr, 0, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(port);
serv_addr.sin_addr.s_addr = inet_addr(host_name);
int so_broadcast;
setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &so_broadcast,
sizeof(so_broadcast));

char buf[256]="client .............";
sockaddr from ;
int len;
sendto(sockfd,buf,sizeof(buf),0,(struct sockaddr*)&serv_addr,sizeof(struct sockaddr_in));
while(1)
{
recvfrom(sockfd,buf,sizeof(buf),0,(struct sockaddr*)&serv_addr,(socklen_t*)&len);
printf("server buf= %s
",buf);
}
}

我們會看到上面接收端綁定的IP是針對子網的廣播，而發送端發送的IP也是針對於子網的廣播，我們可以ROUTE PRINT一下，看看自己電腦的路由表（如果不懂怎麼看，請百度）。如果是雙網卡同網段，那麼到同一個網段的IP將有兩個，所以就接收了兩次，我曾試過發送端綁定255.255.255.255，結果只發送一次，但是讓人不解的是路由表中對於目的地址爲255.255.255.255的依舊是兩個，所以我只能推斷上面那個哥們的程序不是在雙網卡機子上進行的，僅僅是一網卡多IP，因爲電腦只會在某一時刻讓一個網卡工作，而在廣播也只收一次。