Android设备USB转以太网连接Modbus TCP/IP服务器失败排查

我正在开发一款Android平台的Modbus TCP/IP客户端应用，设备已连接USB转以太网转换器，尝试以笔记本电脑作为服务器通信时连接失败，报错信息如下：

java.net.ConnectionException: failed to connect to /192.168.29.244 (port 502) from /::(port 0): connect failed: ENETUNREACH (network is unreachable)

我已将手机设置为关闭Wi-Fi、移动数据或开启飞行模式，避免无线信号干扰。目前测试结果如下：

• Android设备与笔记本电脑处于同一Wi-Fi网络时，通信正常
• 设备通过USB以太网直连笔记本电脑时出现上述连接错误
• 设备通过Wi-Fi所在的网络交换机有线连接时，通信正常

相关核心代码如下：

Thread t1 = new Thread(() -> {
                /* The important instances of the classes mentioned before */
                con = null; //the connection

                /* Variables for storing the parameters */
                int port = Integer.parseInt(etPort.getText().toString());

                String ip = etIP.getText().toString();
                try {
                    InetAddress addr = InetAddress.getByName(ip);//the slave's address

                    con = new TCPMasterConnection(addr);
                    con.setPort(port);
                    con.setTimeout(500);
                    Log.d("Connection parameters", "Timeout: " + con.getTimeout() + " Port: " + port);
                    con.connect();
                    runOnUiThread(() -> {
                        tv.setText("Connected!!!");
                        connect.setText("Disconnect");
                    });
                } catch (Exception e) {
                    e.printStackTrace();
                    Log.e("Error!", e.toString());
                    runOnUiThread(() -> {
                        tv.setText(e.toString());
                    });
                }
            });
            if (connect.getText().equals("Connect"))
                t1.start();
            else {
                Log.d("In diconnect", "Coonection closed!");
                con.close();
                connect.setText("Connect");
                tv.setText("Disconnected!!!");
            }

内容的提问来源于stack exchange，提问作者Darshan Modi