在Linux中使用Java Netty时，多播发布数据包不起作用

我正在用Netty编写一个多播发送器。我在Linux中使用“ngrep”嗅探端口，但我看不到数据包。。。我检查了示例和代码，但我不明白为什么它不起作用。你知道我的代码有什么问题吗？
谢谢

以下是我的代码：

出版商

public class Publisher implements Runnable {
  private InetSocketAddress groupAddress;
  private NioDatagramChannel ch;
  private AtomicLong sequenceNumber = new AtomicLong(1);

  public Publisher(InetSocketAddress address) throws InterruptedException {
    groupAddress = address;
  }

  @Override
  public void run() {
    EventLoopGroup group = new NioEventLoopGroup();
    try {
      NetworkInterface ni = NetworkInterface.getByName("wlp3s0");
      Enumeration<InetAddress> addresses = ni.getInetAddresses();
      InetAddress localAddress = null;
      while (addresses.hasMoreElements()) {
        InetAddress address = addresses.nextElement();
        if (address instanceof Inet4Address) {
          localAddress = address;
        }
      }

      Bootstrap b =
          new Bootstrap().group(group).channelFactory(new ChannelFactory<NioDatagramChannel>() {
            @Override
            public NioDatagramChannel newChannel() {
              return new NioDatagramChannel(InternetProtocolFamily.IPv4);
            }
          })
          .handler(new LoggingHandler(LogLevel.DEBUG))
          .localAddress(localAddress, groupAddress.getPort())
              .option(ChannelOption.IP_MULTICAST_IF, ni)
              .option(ChannelOption.SO_REUSEADDR, true)
              .handler(new MessageEncoder(groupAddress));

      ch = (NioDatagramChannel) b.bind(groupAddress.getPort()).sync().channel();
      ch.joinGroup(groupAddress, ni).sync();
      ch.closeFuture().await();
    } catch (InterruptedException e) {
      e.printStackTrace();
    } catch (SocketException e) {
      e.printStackTrace();
    } finally {
      group.shutdownGracefully();
    }
  }

  public void publish(List<Message> messages) throws Exception {
    ByteBuffer buffer = Packet.build(sequenceNumber.longValue(), messages);
    if (buffer != null)
      ch.writeAndFlush(buffer.array());
  }
}

public class MessageEncoder extends MessageToMessageEncoder<Message> {

  private final InetSocketAddress remoteAddress;

  public MessageEncoder(InetSocketAddress remoteAddress) {
    this.remoteAddress = remoteAddress;
    }
  
  @Override
  protected void encode(ChannelHandlerContext ctx, Message msg, List<Object> out) throws Exception {
    ByteBuffer b = msg.encode();
    ByteBuf buffer = ctx.alloc().buffer(b.array().length);
    out.add(new DatagramPacket(buffer, remoteAddress));
  }

}

嗅探

$ sudo ngrep -d any port 21102

$ sudo ngrep -d any port 21102