Question

我有一个代码，其中发送多播数据报。一段重要的代码：

uint32_t port;
int sockfd, err_ip;
const uint32_t sizebuff = 65535 - (20 + 8);
unsigned char *buff = (unsigned char *) malloc(sizebuff);
struct sockaddr_in servaddr, cliaddr;
struct in_addr serv_in_addr;
struct ip_mreq req;

port = str2uint16(cmdsrv->ipport);
bzero(buff, (size_t)sizebuff);
bzero(&servaddr, sizeof(servaddr));
bzero(&serv_in_addr, sizeof(serv_in_addr));
err_ip = inet_aton(cmdsrv->ipaddr, &serv_in_addr);

if(( err_ip != 0 ) && ( port != 0 )) {
   servaddr.sin_family = AF_INET;
   servaddr.sin_addr = serv_in_addr;
   servaddr.sin_port = htons(port);
   memcpy(&req.imr_multiaddr,&serv_in_addr,sizeof(req.imr_multiaddr));
   req.imr_interface.s_addr = INADDR_ANY;
   sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

   if( sockfd == -1 ) {
      int outerror = errno;
      char *retstr = "Couldn't open socket\n";
      pthread_exit(retstr);
   }
   else {
      struct in_addr ifaddr;
      ifaddr.s_addr = INADDR_ANY;
      int optres3 =
         setsockopt( sockfd, IPPROTO_IP, IP_MULTICAST_IF, &ifaddr,
                     sizeof( ifaddr ));
      if( optres3 == -1 ) {
         int perrno = errno;
         char *retstr = "Can't set IP_MULTICAST_IF for socket\n";
         printf( "Error setsockopt: ERRNO = %s\n", strerror( perrno ));
         printf( "%s",retstr );
         pthread_exit(retstr);
      }

      unsigned char ttl = 32;
      int optres2 =
         setsockopt( sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl,
                     sizeof( ttl ));
      if( optres2 == -1 ) {
         int perrno = errno;
         char *retstr = "Can't set IP_MULTICAST_TTL for socket\n";
         printf("Error setsockopt: ERRNO = %s\n",strerror(perrno));
         printf("%s",retstr);
         pthread_exit(retstr);
      }

      int optres =
         setsockopt( sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &req,
                     sizeof( req ));
      if( optres == -1 ) {
         int perrno = errno;
         char *retstr = "Can't join to multicast-group\n";
         printf("Error setsockopt: ERRNO = %s\n",strerror(perrno));
         printf("%s",retstr);
         pthread_exit(retstr);
      }

      // Bind port with socket
      uint16_t cliport;
      cliaddr.sin_family = AF_INET;
      cliaddr.sin_addr.s_addr = INADDR_ANY;

      if( strcmp( cmdsrv->ipport, "16011" ) == 0 ) {
         cliport = str2uint16("16003");
         cliaddr.sin_port = htons(cliport);
      }
      else if( strcmp( cmdsrv->ipport, "16012" ) == 0 ) {
         cliport = str2uint16("16004");
         cliaddr.sin_port = htons(cliport);                     
      }
      else {
         printf("Device hasn't such port");
         pthread_exit(NULL);
      }

      int bindres =
         bind( sockfd, (struct sockaddr*)&cliaddr, sizeof( cliaddr ));
      if( bindres == -1 ) {
         int perrno = errno;
         perror("Error in bind\n");
      }
      // ADD 1 BYTE
      data rawdata;
      rawdata.desc = 23;
      printf( "SIZEOF = %d\n", sizeof( *( cmdsrv->cmd )));
      memcpy( &rawdata.cmd, cmdsrv->cmd, sizeof( *( cmdsrv->cmd )));
      printf( "RAWDATA: desc = %d, cmd = %d\n", rawdata.desc, rawdata.cmd );

      int outerror = 0;
      printf( "Send command to IP:\n addr = %s, port = %d\n",
         inet_ntoa( servaddr.sin_addr ), ntohs( servaddr.sin_port ));
      int size = sendto( sockfd, &rawdata, sizeof( rawdata ), 0,
         (struct sockaddr*)&servaddr, sizeof( servaddr ));
      if( size == -1 ) {
         perror("Can't send command to socket");
      }
      ...

有时程序成功执行（此时我有IP - 192.168.80.122）。我可以通过wireshark捕获我的多播数据报。一切都好。

但如果我将我的IP更改为192.168.1.2，则在调用时会出现错误

int optres =
   setsockopt( sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &req,
               sizeof( req ));

我甚至无法捕获我的多播数据包。什么都没发送。哪里有错误？

Answer 1

如果它适用于一个IP而不适用于另一个IP，那么this可以提供帮助。

“IP_ADD_MEMBERSHIP：没有这样的设备”是什么意思？

这意味着该工具正在尝试使用多播但网络接口不支持它有两种可能的原因：



您的计算机未启用多播支持。例如，在Linux和FreeBSD上，可以编译不支持多播的内核。



您没有组播流量的路由。默认情况下，某些系统不会添加此项，您需要运行。 route add -net 224.0.0.0 netmask 224.0.0.0 eth0（或类似）。如果您只想在单播模式下使用RAT，可以在环回接口上添加组播路由。

Answer 2

仅接收组播需要IP_ADD_MEMBERSHIP和bind()，而使用IP_MULTICAST_IF代替组播组的仅发送成员资格。

调用setsockopt时出错“No such device”

2 个答案:

“IP_ADD_MEMBERSHIP：没有这样的设备”是什么意思？