UDP多播未通过多主机上的localhost传送

Question

我有一台有多个网络接口的机器，我正在尝试使用UDP多播。我把它归结为这个微小的复制程序。

public class Main {
  public static void main(String[] args) throws Exception {
    InetAddress local = InetAddress.getByName("127.0.0.1");  // hangs
//    InetAddress local = InetAddress.getByName("10.0.0.145"); // finishes
    List<NetworkInterface> matchingIfs = new ArrayList<NetworkInterface>();
    Enumeration<NetworkInterface> netIfs = NetworkInterface.getNetworkInterfaces();
    while( netIfs.hasMoreElements() ) {
      NetworkInterface netIf = netIfs.nextElement();
      Enumeration<InetAddress> addrs = netIf.getInetAddresses();
      while( addrs.hasMoreElements() ) {
        InetAddress addr = addrs.nextElement();
        if( addr.equals(local) ) {
          matchingIfs.add(netIf);
          break;
        }
      }
    }

    NetworkInterface netIf = matchingIfs.get(0);
    InetAddress addr = InetAddress.getByName("233.245.29.143");
    int port = 59893;
    DatagramPacket sendPack = new DatagramPacket(new byte[1600],1600);
    DatagramPacket recvPack = new DatagramPacket(new byte[1600],1600);

    System.out.println("Using network interface: " + netIf);

    MulticastSocket send = new MulticastSocket();
    send.setTimeToLive(127);
    send.setNetworkInterface(netIf);

    MulticastSocket recv = new MulticastSocket(port);
    recv.setNetworkInterface(netIf);
    recv.joinGroup(addr);

    sendPack.setData("asdfasdf".getBytes());
    sendPack.setAddress(addr);
    sendPack.setPort(port);

    System.out.println("About to send");
    send.send(sendPack);
    System.out.println("Finished send");

    System.out.println("About to recieve");
    recv.receive(recvPack);
    System.out.println("Finished recieve");
    String s = new String(recvPack.getData(), recvPack.getOffset(), recvPack.getLength());
    System.out.println(s);
  }
}

如果我不拨打setNetworkInterface，当主机有多个网络接口时，此程序将挂起。

当使用127.0.0.1运行时，无论网络接口的数量如何，程序都会等待接收。

当使用10.0.0.145（机器IP地址）运行时，程序将按预期运行。

我的所有测试都在Mac上运行10.8.2。