ESP8266 Community Forum

- Fri Apr 12, 2019 7:42 am #81721 Platform
- Hardware: ESP8266 / ESP-12E
- Core Version: not sure, flashed with NodeMCU ESP8266Flasher.exe (commit d929c51 on 8 Aug 2017) using INTERNAL://NODEMCU
- SDK: SDK:3.0.0-dev(c0f7b44)/Core:2.5.0=20500000/lwIP:1.4.0rc2/BearSSL:6778687
- Development Env: Arduino IDE
- Operating System: Windows

Settings in IDE
- Module: tested with 2 breakouts of NodeMCU v1.0 and Wemos D1 mini R2
- Flash Mode: not sure
- Flash Size: 4MB
- lwip Variant: tested with all v2 types (Lower Memory/Higher Bandwidth)
- Reset Method: not sure, all breakouts have RST btn
- Flash Frequency: 40Mhz
- CPU Frequency: 80Mhz
- Upload Using: SERIAL
- Upload Speed: tested all speeds from 115200 up

Problem Description
First of all, I have search the internet for hours including https://github.com/esp8266/Arduino/issues/4949 not finding a solution!
The sketch connects to a wifi and wants to access a Windows host in LAN using Windows hostname (e.g. `DESKTOP-123` as given in Windows 10 This computer's properties).
The sketch uses 2 methods one after each other (an in loop):
1) ping the host using `ESP8266Ping` library
2) direct call of `WiFi.hostByName()` from `ESP8266WiFi` library
(The ping uses a call to `hostByName` anyway.)
The problem is, that ping from ESP always fails with `DNS lookup error: -5!`
Ping within the same network from another PC host works fine.
Ping from ESP to a host in internet (e.g. `www.google.com`) works fine too.
I have tested this in 8 different LANs with different APs.

I understand, that DNS lookup may not resolve Windows host names (NetBios over TCP is not working here, as it would on a PC host).
Any idea, how to solve this?
Thanks for any help.

Sketch

Code: Select all#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>
#include <ESP8266Ping.h>

ESP8266WiFiMulti WiFiMulti;
String remote_host = "DESKTOP-BGHIGLC";

void setup() {
  Serial.begin(115200);
  Serial.setDebugOutput(true);
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();
  WiFiMulti.addAP("<ssid>", "<pwd>");
}

void loop() {
  if ((WiFiMulti.run() == WL_CONNECTED)) { // wait for WiFi connection
    WiFi.printDiag(Serial);
    Serial.print(">>> PING: ");
    Serial.println(remote_host);
    if (Ping.ping(remote_host.c_str())) {
      Serial.println(">>> PING: Success!!");
    } else {
      Serial.println(">>> PING: Error");
    }
    delay(1000);
    printIPAddressOfHost(remote_host.c_str());  // call to resolve host name to IP
  }
  delay(3000);
}

void printIPAddressOfHost(const char* host) {
  IPAddress resolvedIP;
  Serial.print(">>> Resolve DNS: ");
  Serial.print(host);
  Serial.print(" IP: ");
  if (!WiFi.hostByName(host, resolvedIP)) {
    Serial.println(">>> DNS lookup failed.");
  } else {
    Serial.println(resolvedIP);
  }
}


Debug Messages
In the debug stream `*********` replaces real SSID and password.

Code: Select allSDK:3.0.0-dev(c0f7b44)/Core:2.5.0=20500000/lwIP:1.4.0rc2/BearSSL:6778687
----------------------------------------
[SETUP] WAIT 4...
[SETUP] WAIT 3...
[SETUP] WAIT 2...
[SETUP] WAIT 1...
bcn 0
del if1
usl
mode : sta(80:7d:3a:74:f3:e3)
add if0
[WIFI][APlistAdd] add SSID: *********
[WIFI] delete old wifi config...
[WIFI] start scan
wifi evt: 8
scandone
[WIFI] scan done
[WIFI] 7 networks found
       0: [1][CC:5D:4E:ED:15:F8] CAT_CAFE (-63) *
 --->  1: [6][30:45:96:91:E1:F2] ********* (-47) *
       2: [8][AC:22:05:62:D6:6C] UPC68FBA54 (-86) *
       3: [11][EC:43:F6:AD:0D:7E] CAT_BYRO (-84) *
       4: [11][02:15:99:9E:F2:B3] DIRECT-cBML-2160 (-77) *
       5: [13][60:31:97:7B:BE:5A] CAT_CAFE (-82) *
       6: [13][00:13:F7:95:28:82] 225-162-35 (-85) *
[WIFI] Connecting BSSID: 30:45:96:91:E1:F2 SSID: ********* Channel: 6 (-47)
wifi evt: 2
scandone
state: 0 -> 2 (b0)
state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 5
cnt
state: 5 -> 2 (4a0)
rm 0
wifi evt: 1
STA disconnect: 4
reconnect
state: 2 -> 0 (0)
scandone
state: 0 -> 2 (b0)
state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 3
cnt

connected with *********, channel 6
dhcp client start...
wifi evt: 0
[WIFI] Connecting Failed (6).
ip:192.168.43.25,mask:255.255.255.0,gw:192.168.43.1
wifi evt: 3
......................................
Mode: STA
PHY mode: N
Channel: 6
AP id: 0
Status: 5
Auto connect: 1
SSID (6): *********
Passphrase (10): *********
BSSID set: 1
>>>IP: 192.168.43.25
>>>Subnet mask: 255.255.255.0
>>>Gataway IP: 192.168.43.1
>>>Default hostname: ESP_74F3E3
>>> PING: DESKTOP-BGHIGLC
[hostByName] request IP for: DESKTOP-BGHIGLC
[hostByName] Host: DESKTOP-BGHIGLC lookup error: -5!
>>> PING: Error
>>> DNS #1, #2 IP: 192.168.43.1, (IP unset)
>>> Resolve DNS: DESKTOP-BGHIGLC IP: [hostByName] request IP for: DESKTOP-BGHIGLC
[hostByName] Host: DESKTOP-BGHIGLC lookup error: -5!
>>> DNS lookup failed.
......................................
Mode: STA
PHY mode: N
Channel: 6
AP id: 0
Status: 5
Auto connect: 1
SSID (6): *********
Passphrase (10): *********
BSSID set: 1
>>>IP: 192.168.43.25
>>>Subnet mask: 255.255.255.0
>>>Gataway IP: 192.168.43.1
>>>Default hostname: ESP_74F3E3
>>> PING: http://www.google.com
[hostByName] request IP for: http://www.google.com
[hostByName] Host: http://www.google.com IP: 172.217.23.228
>>> PING: Success!!
ping 5, timeout 0, total payload 160 bytes, 5035 ms
>>> DNS #1, #2 IP: 192.168.43.1, (IP unset)
>>> Resolve DNS: http://www.google.com IP: [hostByName] request IP for: http://www.google.com
[hostByName] Host: http://www.google.com IP: 172.217.23.228
172.217.23.228


- Thu Apr 18, 2019 5:44 am #81862 maybe "mdns" might be a solution to your problem ...

- Thu Apr 18, 2019 7:01 am #81864 Hi, thanks for mentioning. However, I am not sure, it is the right place to go. The reason is, that the described problem cannot be reproduced always with the same setup. For example, if the AP is created from mobile, it mostly works. Any other AP (router etc.) does not work at all. No idea, why is that...

- Thu Apr 18, 2019 8:26 am #81869

maybe "mdns" might be a solution to your problem ...

Well, thanks for mentioning, however, what should I search there? The target server/PC is reachable from any other PC in the LAN. It is not reachable from an ESP8266 board!?!