ESP8266 cannot create TCP connections to this particular server

Question

EDIT: I have created an issue about this here: https://github.com/esp8266/Arduino/issues/4593

---

I have this server: 185.205.210.197 (Check that it works: http://185.205.210.197/)

And I have this code in my ESP8266:

#include <ESP8266WiFi.h>

#define HOST "185.205.210.197"
#define PORT 80
#define WIFI_SSID "SSID"
#define WIFI_PSW "PASSWORD"

const char* ssid = WIFI_SSID;
const char* password = WIFI_PSW;

void setup () {
  Serial.begin(115200);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(5000);
    Serial.println("Connecting to Wifi...");
  }

  while(!pingServer()) {
    delay(3000); //Send a request every 3 seconds
  }
}


void loop() {}


bool pingServer() {
  WiFiClient client;

  if (!client.connect(HOST, PORT)) {
    Serial.println("connection failed");
    return false;
  }

  Serial.println("connection success!");
  return true;
}

The expected result: Connection success, but got connection failed.

If I try connecting with my PC, it works, only with ESP8266 it doesn't.

Tapping with Wireshark I suspect that there is a problem with ESP8266 TCP packets, here I leave them for you to analyze:

PC TCP connection request (which works):

000030006b081c001a48ea4c0000000010009e098004dba400000000800401009e090b221f000000c603000004000000880254009801a7ad45b7000af5f4e90c000af5f4e90c603c0000aaaa0300000008004500003c000040003706cb37b9cdd2c5c0a82b490050df312dfea1498c6ac92aa0120000079c00000204058c0402080a336f35554aeb0fe90103030700ead7d1

ESP8266 TCP connection request (which receives no response from server):

000019006f080000952a9f520000000012049e098004daa1000801a200000af5f4e90c2c3ae80f137f000af5f4e90c5000aaaa0300000008004500002c00030000ff06431dc0a82b70b9cdd2c5c00100500000196d000000006002086040f80000020402189ccdd933

What I've also checked:

• The ESP connects fine to other servers.

• There is no firewall blocking the connection between ESP and the server.

• I've tried this in different networks and conditions, the error persists.

• Other computers can connect to the server, so ESP should be able as well.

• Tried with different ESP8266 boards to rule out hardware malfunctioning.

• I am using NODEMCU V0.9 board (original firmware) with Arduino IDE and this ESP8266 library.

How to replicate:

1. Using the latest Arduino IDE and ESP8266 library.

2. Check that the test server works at http://185.205.210.197:80/ (just open this link basically and see that is running nginx).

3. Copy and upload the code above to your ESP8266 (NODEMCU or similar).

4. Open the Arduino IDE console/monitor and confirm that no connection is established to port 80.

5. Rage in admiration for such a strange bug.

I've opened an Issue for this: https://github.com/esp8266/Arduino/issues/4593

Answer 1

Not a cookie cutter answer, I did a quick test and my ESP8266 does connect to you nginx. Of course you do not accept the params from my fridge, but this is what I see in the log.

7007 :
7010 :

For online documentation and support please refer to
7012 : nginx.org.

7015 : Commercial support is available at
7018 : nginx.com.

7020 :
7022 :

Thank you for using nginx.

7024 :
7026 :
7028 : HTTP : closing connection

You should be able to see that on your side as well.

I am using letscontrolit/ESPEASY https://github.com/letscontrolit/ESPEasy

And their code to connect looks like

  // Use WiFiClient class to create TCP connections
  WiFiClient client;
  if (!ControllerSettings.connectToHost(client))
  {
    connectionFailures++;
    addLog(LOG_LEVEL_ERROR, F("HTTP : connection failed"));
    return false;
}

  boolean connectToHost(WiFiClient &client) {
    if (!checkHostReachable(true)) {
      return false; // Host not reachable
    }
    byte retry = 2;
    bool connected = false;
    while (retry > 0 && !connected) {
      --retry;
      connected = client.connect(getIP(), Port);
      if (connected) return true;
      if (!checkHostReachable(false))
        return false;
    }
    return false;
}

I am using generic HTTP for my controller which here: https://github.com/letscontrolit/ESPEasy/blob/503fd3555e010b08b48fb2dc18290ef120005308/src/_C008.ino

You could try the connect to function to see if that works for you.