Cross post with https://stackoverflow.com/questions/52596484/connect-android-and-pi-3-via-network-socket-using-pi-3-as-an-access-point, please delete if this isn't allowed.

My plan here is to create an access point on the Pi 3 using the interface wlan0 which has been setup using hostapd. I run the command hostapd /etc/hostapd/hostapd.conf to start up the network and then I want to connect to it with the Android and setup a socket.

Currently, the network enables on the Pi 3 without issue, but creating the socket on Android is throwing

java.net.ConnectException: failed to connect to / (port 80) after 500ms: connect failed: ENETUNREACH (Network is unreachable).

I am using the IP of Pi's wlan0 to create my socket as you can see (on Android code). I will post the output of the Pi's Python script as well as some information about the network.

I have the following Python 3 code on my Pi 3 (server):

import socket
import os

os.system('hostapd /etc/hostapd/hostapd.conf &')
print('started access point service')

serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.bind(('', 80))

connection, address = serversocket.accept()

b = connection.recv(1024)


Android code regarding the wifi socket connection (client). Joins the network using its' SSID:

        // enable Wifi

        // connect to the network access point created by the Pi 3
        WifiConfiguration wifiConfiguration = new WifiConfiguration();
        wifiConfiguration.SSID = "\"" + blackBoxSSID + "\"";
        wifiConfiguration.preSharedKey = "\"" + blackBoxNetworkPassword + "\"";
        wifiConfiguration.status = WifiConfiguration.Status.ENABLED;

        int netID = wifiManager.addNetwork(wifiConfiguration);
        if (netID == -1) {
            netID = getExistingNetworkID(wifiConfiguration.SSID);

        wifiManager.enableNetwork(netID, true);

        WifiInfo wifiInfo = wifiManager.getConnectionInfo();

        Log.d(TAG, "current netID " + netID + ", current SSID " + wifiInfo.getSSID());
        Log.d(TAG, "current IP of wifi device: " + wifiInfo.getIpAddress() + ", HW address: " + wifiInfo.getMacAddress());

        // start the server socket process

Helper functions:

    private void startServerSocket() {
            Log.i(TAG, "Starting server socket thread");
            Thread serverSocketThread = new Thread(new Runnable() {
                public void run() {
                    try {
                        Socket socket = new Socket();
                        socket.connect(new InetSocketAddress("", 80), 500);
                        DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
                        dataOutputStream.writeBytes("Hello black box");
                        dataOutputStream.writeBytes("Hello black box");
                        dataOutputStream.writeBytes("Hello black box");
                        dataOutputStream.writeBytes("Hello black box");
                        dataOutputStream.writeBytes("Hello black box");
                        dataOutputStream.writeBytes("Hello black box");
                    } catch (IOException e) {
                        Log.e(TAG, "Error creating ServerSocket and Socket object:", e);
            Log.d(TAG, "started server socket thread");


private int getExistingNetworkID(String SSID) {
        WifiManager wifiManager = (WifiManager) mContext.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
        List<WifiConfiguration> configuredNetworks = wifiManager.getConfiguredNetworks();
        if (configuredNetworks != null) {
            for (WifiConfiguration existingConfig : configuredNetworks) {
                if (existingConfig.SSID.equals(SSID)) {
                    return existingConfig.networkId;
        return -1;

here's the manifest file:

<!-- Wifi/Internet-related permissions -->
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
    <uses-permission android:name="android.permission.INTERNET"/>

The Android code returns

current netID 617, current SSID "NetworkName" current IP of wifi device: 0, HW address: <hw address of something but not wlan0>, which means the correct network is connected without issue.

The Python code returns

started access point service
Configuration file: /etc/hostapd/hostapd.conf
Failed to create interface mon.wlan0: -95 (Operation not supported)
wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
wlan0: Could not connect to kernel driver
Using interface wlan0 with hwaddr <wlan0 hw address> and ssid "NetworkName"
listening on port 80
wlan0: interface state COUNTRY_UPDATE->ENABLED
wlan0: AP-ENABLED 

and all wifi devices I have can see the network and connect using the password.

For more info here is the hostapd.conf file:


sorry about the indentation inside some of the code snippets, using the {} code button puts this in and I can't seem to get rid of it without removing the code formatting.


Here is the contents of /etc/dnsmasq.conf:

interface=wlan0 dhcp-range=,,,24h

dnsmasq and hostapd services are both active (running)

If I manually go and select Wifi then connect using the WPA password, the device associates then disassociates with the Pi 3, then reads AP-STA-CONNECTED with pairwise key handshake completed (RSN). So clearly my Android code is doing something weird. But doing this crashes the app with a RuntimeException; unable to instantiate receiver (wifiReceiver - which doesn't exist) and ClassNotFoundException: didn't find class (wifiReceiver) on path: DexPathList. It seems like this is a completely internal call as well, there are no tracebacks to my actual code.

  • tl;dr but have scanned the question but could not find what is the specific problem with Raspberry Pi. I only read that it works as expected as access point but Android has a problem. Is Android also running on a RasPi?
    – Ingo
    Oct 1, 2018 at 22:00

1 Answer 1



I was creating working on a .NET app through my FreeNAS server and my router started filtering out my connections because it thought my server was under attack; unfortunately I cannot remember the specific reason. I cannot tell you how much frustration this caused me.

Check your router log and see if it is sensing an attack from your "access point". There may be a firewall or something else blocking the connection as well, I don't know what kind of firewalls would be in effect here.


Log.d(TAG, "started server socket thread");

Does this ever log anything

And I am not familiar with this threading stuff, but won't "startServerSocket" just exit - shouldn't there be some kind of block or asynchronous wait?

(Note: I would have posted a comment, but it says I am too new)

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