Linux内核无法接收多播

Question

我用 CONFIG_IP_MULTICAST=y 构建了一个 Linux 内核，但是在这个内核中没有接收到 UDP 多播包，而 UDP 单播运行良好。

ethtool -S eth0 | grep multicast                         
txmulticastframes_g: 0                   
txmulticastframes_gb: 0             
rxmulticastframes_g: 0

有什么提示可以解决这个问题吗？

谢谢。福雷斯特 G

============================================= ==================================补充:
tcpdump 可以得到数据包

root@JHI # ./tcpdump port 3702
device eth0 entered promiscuous mode
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
-7:-48:-19.4151 IP 192.168.42.212.3702 > 239.255.255.250.3702: UDP, length 787
-7:-48:-19.4661 IP 192.168.42.212.3702 > 239.255.255.250.3702: UDP, length 803
^C
2 packets captured
2 padevice eth0 left promiscuous mode
ckets received by filter
0 packets dropped by kernel

我用 gSOAP 编写了这个 WS-devicediscovery 函数。它适用于 X86 机器。在 ARM 设备上运行时，它可以发送 igmp 数据包但收不到任何东西。

void wsdd()  
{      
    struct soap *soap_udp;   
    struct ip_mreq mreq;   

    soap_udp=soap_new();  
    soap_init1(soap_udp, SOAP_IO_UDP|SOAP_IO_FLUSH);  

    if (!soap_valid_socket(soap_bind(soap_udp, NULL, 3702, 100)))  
    {      
        soap_print_fault(soap_udp, stderr);  
    }  

    mreq.imr_multiaddr.s_addr = inet_addr("239.255.255.250");  
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);  

    if(setsockopt(soap_ud->master,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq))==-1)     {  
        perror("membership error\n");  
    }

    int loop = 1;  
    int sock_opt = 1;
    if ((setsockopt(soap_udp->master, SOL_SOCKET, SO_REUSEADDR, (void *) &sock_opt,  
                    sizeof (sock_opt))) == -1) {  
        printf("setsockopt\n");  
    }  
    if ((setsockopt(soap_udp->master, IPPROTO_IP, IP_MULTICAST_LOOP,  
                       &loop, sizeof (loop))) == -1) {  
        printf("setsockopt\n");  
    }

    while(1){  
        soap_accept(soap_udp);
        soap_serve(soap_udp);   
        soap_end(soap_udp); 
    }  
} 

然后这些我都试过了还是不行

route add -net 224.0.0.0 netmask 240.0.0.0 eth0
echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter

Answer 1

通过改变..解决了问题

ifconfig eth0 promisc

谁能解释一下原理？