I wanted to give an update on my findings, finally able to get multicast to work. I also had to comment out this line: datagramChannel.connect(new InetSocketAddress(sendingHost, sendingPort)); @Override public void open(final InetAddress nicAddress, final int port, final int maxBufferSize) throws IOException { stopped = false; // Use INET protocol family for IPv4 multicast if (isMulticast) { datagramChannel = DatagramChannel.open(StandardProtocolFamily.INET); } else { datagramChannel = DatagramChannel.open(); } datagramChannel.configureBlocking(false); if (maxBufferSize > 0) { datagramChannel.setOption(StandardSocketOptions.SO_RCVBUF, maxBufferSize); final int actualReceiveBufSize = datagramChannel.getOption(StandardSocketOptions.SO_RCVBUF); if (actualReceiveBufSize < maxBufferSize) { logger.warn("Attempted to set Socket Buffer Size to {} bytes but could only set to {} bytes. You may want to consider changing the Operating System's maximum receive buffer", maxBufferSize, actualReceiveBufSize); } } // we don't have to worry about nicAddress being null here because InetSocketAddress already handles it datagramChannel.setOption(StandardSocketOptions.SO_REUSEADDR, true); datagramChannel.socket().bind(new InetSocketAddress(port)); // if a sending host and port were provided then connect to that specific address to only receive // datagrams from that host/port, otherwise we can receive datagrams from any host/port if (sendingHost != null && sendingPort != null) { // This seems to not allow the multicast to work. Therefore, I commented it out. // datagramChannel.connect(new InetSocketAddress(sendingHost, sendingPort)); } selector = Selector.open(); datagramChannel.register(selector, SelectionKey.OP_READ); // Join multicast group if specified if (isMulticast) { InetAddress group = InetAddress.getByName(multicastGroup); // Determine which network interface to use for multicast NetworkInterface networkInterface; if (multicastInterface != null && !multicastInterface.isEmpty()) { // Use specified interface networkInterface = NetworkInterface.getByName(multicastInterface); if (networkInterface == null) { // Try as an IP address networkInterface = NetworkInterface.getByInetAddress(InetAddress.getByName(multicastInterface)); } } else { // Use the NIC address interface if none specified networkInterface = NetworkInterface.getByInetAddress(nicAddress); } if (networkInterface == null) { throw new IOException("Could not find network interface for multicast"); } // Join the multicast group on the selected interface membershipKey = datagramChannel.join(group, networkInterface); logger.info("Joined multicast group {} on interface {}", multicastGroup, networkInterface.getDisplayName()); } }
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