Arduino D1 wifi: Error creating a wifi same name with wifi connected.

Projects Programming
1

I use Arduino D1 connected to my Wifi "giadinh" - IP gateway 192.168.1.1.
And follow the example AdvancedWebserver.ino and program runs very well on the device.

However there are some errors as follows:

If the network connection from the outside to the control device (open - Nat modem port)

D1 generate a wifi wifi same name "giadinh" with 192.168.4.1 ip is making other devices such as laptops or phones connected to D1. This equipment should not be out on the internet.

my wifi name is "giadinh" gateway 192.168.1.1
after D1 connect to "giadinh" D1's IP is 192.168.1.4 (D1 use good, PC browser: 192.168.1.4 is turn on/off led good)

my phone conneted with "giadinh", IP my phone is 192.168.4.2 (no Internet)

turn off D1
my phone conneted with "giadinh", IP my phone is 192.168.1.7 (good Internet)

Please ! fix error. Thank !

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>

const char *ssid = "giadinh";
const char *password = "mypasswordgd";

ESP8266WebServer server ( 80 );

const int led = 13;

void handleRoot() {
	digitalWrite ( led, 1 );
	char temp[400];
	int sec = millis() / 1000;
	int min = sec / 60;
	int hr = min / 60;

	snprintf ( temp, 400,

"<html>\
  <head>\
    <meta http-equiv='refresh' content='5'/>\
    <title>ESP8266 Demo</title>\
    <style>\
      body { background-color: #cccccc; font-family: Arial, Helvetica, Sans-Serif; Color: #000088; }\
    </style>\
  </head>\
  <body>\
    <h1>Hello from ESP8266!</h1>\
    <p>Uptime: %02d:%02d:%02d</p>\
    <img src=\"/test.svg\" />\
  </body>\
</html>",

		hr, min % 60, sec % 60
	);
	server.send ( 200, "text/html", temp );
	digitalWrite ( led, 0 );
}

void handleNotFound() {
	digitalWrite ( led, 1 );
	String message = "File Not Found\n\n";
	message += "URI: ";
	message += server.uri();
	message += "\nMethod: ";
	message += ( server.method() == HTTP_GET ) ? "GET" : "POST";
	message += "\nArguments: ";
	message += server.args();
	message += "\n";

	for ( uint8_t i = 0; i < server.args(); i++ ) {
		message += " " + server.argName ( i ) + ": " + server.arg ( i ) + "\n";
	}

	server.send ( 404, "text/plain", message );
	digitalWrite ( led, 0 );
}

void setup ( void ) {
	pinMode ( led, OUTPUT );
	digitalWrite ( led, 0 );
	Serial.begin ( 115200 );
	WiFi.begin ( ssid, password );
	Serial.println ( "" );

	// Wait for connection
	while ( WiFi.status() != WL_CONNECTED ) {
		delay ( 500 );
		Serial.print ( "." );
	}

	Serial.println ( "" );
	Serial.print ( "Connected to " );
	Serial.println ( ssid );
	Serial.print ( "IP address: " );
	Serial.println ( WiFi.localIP() );

	if ( MDNS.begin ( "esp8266" ) ) {
		Serial.println ( "MDNS responder started" );
	}

	server.on ( "/", handleRoot );
	server.on ( "/test.svg", drawGraph );
	server.on ( "/inline", []() {
		server.send ( 200, "text/plain", "this works as well" );
	} );
	server.onNotFound ( handleNotFound );
	server.begin();
	Serial.println ( "HTTP server started" );
}

void loop ( void ) {
	server.handleClient();
}

void drawGraph() {
	String out = "";
	char temp[100];
	out += "<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\" width=\"400\" height=\"150\">\n";
 	out += "<rect width=\"400\" height=\"150\" fill=\"rgb(250, 230, 210)\" stroke-width=\"1\" stroke=\"rgb(0, 0, 0)\" />\n";
 	out += "<g stroke=\"black\">\n";
 	int y = rand() % 130;
 	for (int x = 10; x < 390; x+= 10) {
 		int y2 = rand() % 130;
 		sprintf(temp, "<line x1=\"%d\" y1=\"%d\" x2=\"%d\" y2=\"%d\" stroke-width=\"1\" />\n", x, 140 - y, x + 10, 140 - y2);
 		out += temp;
 		y = y2;
 	}
	out += "</g>\n</svg>\n";

	server.send ( 200, "image/svg+xml", out);
}