sash sash - 1 month ago 22
Android Question

TCP\IP client - EHOSTUNREACH (No route to host)

I am trying to develop a client server TCP/IP application. I have a server running on my PC and the client app is running on the mobile. They both are in the same Wi-Fi network, but I cannot establish a connection between them. While debugging the client Android app showed the following error:

09-21 01:08:40.422: W/System.err(8536): java.net.ConnectException: failed to connect to /192.168.15.115 (port 4449): connect failed: EHOSTUNREACH (No route to host)
09-21 01:08:40.453: W/System.err(8536): at libcore.io.IoBridge.connect(IoBridge.java:114)
09-21 01:08:40.453: W/System.err(8536): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
09-21 01:08:40.453: W/System.err(8536): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
09-21 01:08:40.453: W/System.err(8536): at java.net.Socket.startupSocket(Socket.java:566)
09-21 01:08:40.453: W/System.err(8536): at java.net.Socket.tryAllAddresses(Socket.java:127)
09-21 01:08:40.453: W/System.err(8536): at java.net.Socket.<init>(Socket.java:177)
09-21 01:08:40.453: W/System.err(8536): at java.net.Socket.<init>(Socket.java:149)
09-21 01:08:40.453: W/System.err(8536): at sabarish.example.client_mobile.MainActivity$1.onClick(MainActivity.java:61)
09-21 01:08:40.453: W/System.err(8536): at android.view.View.performClick(View.java:3511)
09-21 01:08:40.453: W/System.err(8536): at android.view.View$PerformClick.run(View.java:14105)
09-21 01:08:40.453: W/System.err(8536): at android.os.Handler.handleCallback(Handler.java:605)
09-21 01:08:40.453: W/System.err(8536): at android.os.Handler.dispatchMessage(Handler.java:92)
09-21 01:08:40.453: W/System.err(8536): at android.os.Looper.loop(Looper.java:137)
09-21 01:08:40.453: W/System.err(8536): at android.app.ActivityThread.main(ActivityThread.java:4424)
09-21 01:08:40.453: W/System.err(8536): at java.lang.reflect.Method.invokeNative(Native Method)
09-21 01:08:40.453: W/System.err(8536): at java.lang.reflect.Method.invoke(Method.java:511)
09-21 01:08:40.453: W/System.err(8536): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-21 01:08:40.453: W/System.err(8536): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-21 01:08:40.453: W/System.err(8536): at dalvik.system.NativeStart.main(Native Method)
09-21 01:08:40.457: W/System.err(8536): Caused by: libcore.io.ErrnoException: connect failed: EHOSTUNREACH (No route to host)
09-21 01:08:40.457: W/System.err(8536): at libcore.io.Posix.connect(Native Method)
09-21 01:08:40.457: W/System.err(8536): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85)
09-21 01:08:40.457: W/System.err(8536): at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
09-21 01:08:40.457: W/System.err(8536): at libcore.io.IoBridge.connect(IoBridge.java:112)
09-21 01:08:40.457: W/System.err(8536): ... 18 more


The code I am using:

public class MainActivity extends Activity {
private Socket client;
private PrintWriter printwriter;
private EditText textField;
private Button button;
private String messsage;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

textField = (EditText) findViewById(R.id.editText1); //reference to the text field
button = (Button) findViewById(R.id.button1); //reference to the send button


button.setOnClickListener(new View.OnClickListener() {

public void onClick(View v) {

messsage = textField.getText().toString(); //get the text message on the text field
textField.setText(""); //Reset the text field to blank

try {

client = new Socket("192.168.15.115", 4449); //connect to server
printwriter = new PrintWriter(client.getOutputStream(),true);
printwriter.write(messsage); //write the message to output stream

printwriter.flush();
printwriter.close();
client.close(); //closing the connection

} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
});

}


What am I doing wrong?

Answer

The no route error indicates that when the TCP connection was attempted, the connection failed because the underlying protocol software could not find a network node to network node route to the designated target node.

The fix is somewhat operating system dependent but it mainly requires you to set up your routing tables so that the device from which you are trying to connect is able to figure out how to reach the device to which you want to connect.

Normally you specify a gateway to which when you attempt to connect, the connection request goes out the network gateway to be resolved by other information technology devices such as routers, etc.

This looks to be an Android device, so the first thing is to make sure that you have connectivity whether WiFi or cell. Another would be to make sure that the WiFi or cell is turned on and operational.

The IP address you specify is normally within a private sub-net. So thing to check is is whether the device that you are trying to connect to is on the same sub-net that your device is on.

Here is a document on sub-nets and routing.