code: public ChannelFuture block(InetAddress multicastAddress, InetAddress sourceToBlock) {
          try {
              block(multicastAddress, NetworkInterface.getByInetAddress(getLocalAddress().getAddress()), sourceToBlock);
          } catch (SocketException e) {
              return failedFuture(this, e);
          }
          return succeededFuture(this);
      }
docs: Block the given sourceToBlock address for the given multicastAddress