【Linux网络编程】Linux多播问题（No such device）解决方法

多播的测试代码如下：

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

#define PORT 10086
#define SIZE 128


int main(void)
{
    int ret = -1;
    int sockfd = -1;
    int i = 0;
    char buf[SIZE];
    struct sockaddr_in addr;
    struct sockaddr_in from;
    //组播相关结构体
    struct ip_mreq req;
    socklen_t len = sizeof(from);

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sockfd)
    {
        perror("socket"); 
        goto err0;
    }

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = INADDR_ANY;
    //inet_pton(AF_INET, "172.16.1.88", &addr.sin_addr); 

    ret = bind(sockfd, (void*)&addr, sizeof(addr));
    if (-1 == ret)
    {
        perror("bind"); 
        goto err1;
    }

    printf("UDP Server %s: %d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));

    //加入多播组
    req.imr_multiaddr.s_addr = inet_addr("224.0.0.88");
    //将本机加入多播组
    req.imr_interface.s_addr = INADDR_ANY;

    //加入多播组
    ret = setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &req, sizeof(req));
    if (ret < 0)
    {
        perror("setsockopt"); 
        goto err0;
    }

    while(1)
    {
        memset(buf, 0, SIZE);

        ret = recvfrom(sockfd, buf, SIZE, 0, (void*)&from, &len);
        buf[ret] = 0;

        printf("recv from: %s:%d  %s\n", inet_ntoa(from.sin_addr), ntohs(from.sin_port), buf);
        i++;
        //退出循环
        if (10 == i)
            break;
    }

    ret = setsockopt(sockfd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &req, sizeof(req));
    if (ret < 0)
    {
        perror("setsockopt"); 
        goto err0;
    }

    //退出组播组之后 测试是否可以收到组播包
    while(1)
    {
        memset(buf, 0, SIZE);

        ret = recvfrom(sockfd, buf, SIZE, 0, (void*)&from, &len);
        buf[ret] = 0;

        printf("recv from: %s:%d  %s\n", inet_ntoa(from.sin_addr), ntohs(from.sin_port), buf);
        i++;
        //退出循环
        if (10 == i)
            break;
    }




    close(sockfd);
    return 0;
err1:
    close(sockfd);
err0:
    return -1;
}

在ubuntu编译运行时，出现如下的错误：

查询相关资料得到的答案如下：

It means that the tool is trying to use multicast but the network interface doesn't support it There are two likely causes:

·Your machine doesn't have multicast support enabled. For example, on Linux and FreeBSD it is possible to compile a kernel which doesn't support multicast.  

·You don't have a route for multicast traffic. Some systems don't add this by default, and you need to run：

​route add -net 224.0.0.0 netmask 255.255.255.255 eth0(or similar)​. If you wish to use RAT in unicast mode only, it is possible to add the multicast route on the loopback interface.

这主要和当前的网络配置有关，因为多播IP地址没有加入到路由表中。

​解决方法​：把需要用到的多播地址(如本例的224.0.0.88)加入到路由表中，命令如下：

​sudo route add -net 224.0.0.88 netmask 255.255.255.255 eth0​

224.0.0.88：为当前使用的多播IP地址

eth0：为当前使用的有效网卡

其它辅助命令：

​sudo route del -net 224.0.0.88 netmask 255.255.255.255 eth0​ //把224.0.0.88从路由表中删除

​route -n​ //查看路由表信息

具体操作过程如下图：