【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 
#include 
#include 
#include 
#include 
#include 
#include 

#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：