ESP8266 fail to connect MQTT broker

Question

I am using NodeMCU dev board with ESP8266 WIFI.

Every time I try to connect to my local broker it returns this error:

failed, rc=-2 try again in 5 seconds

I am using Ubuntu 18.04, my local brokers are Mosquitto and EQMTT. I tried both of them through pubsubclient library and it doesn't connect. Using MQTT Box works connecting to my local brokers. Connecting to my WiFi also works. When I connect to a MQTT broker using pubsubclient e.g. mqtt://test.mosquitto.org:1883/ it works. It just doesn't seem to work with local broker. This is the code:

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
// Update these with values suitable for your network.
const char* ssid = "mywifi";
const char* password = "password";
const char* mqtt_server = "127.0.0.1";
WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;
void setup() {
 pinMode(D7, OUTPUT); // Initialize the BUILTIN_LED pin as an output
 Serial.begin(9600);
 setup_wifi();
 client.setServer(mqtt_server, 1883);
 client.setCallback(callback);
}
void setup_wifi() {
 delay(10);
 // We start by connecting to a WiFi network
 Serial.println();
 Serial.print("Connecting to ");
 Serial.println(ssid);
 WiFi.begin(ssid, password);
 while (WiFi.status() != WL_CONNECTED) {
 delay(500);
 Serial.print(".");
 }
 Serial.println("");
 Serial.println("WiFi connected");
 Serial.println("IP address: ");
 Serial.println(WiFi.localIP());
}
void callback(char* topic, byte* payload, unsigned int length) {
 Serial.print("Message arrived [");
 Serial.print(topic);
 Serial.print("] ");
 for (int i = 0; i < length; i++) {
 Serial.print((char)payload[i]);
 }
 Serial.println();
 // Switch on the LED if an 1 was received as first character
 if ((char)payload[0] == '1') {
 digitalWrite(D7, LOW); // Turn the LED on (Note that LOW is the voltage level
 // but actually the LED is on; this is because
 // it is acive low on the ESP-01)
 } else {
 digitalWrite(D7, HIGH); // Turn the LED off by making the voltage HIGH
 }
}
void reconnect() {
 // Loop until we're reconnected
 while (!client.connected()) {
 Serial.print("Attempting MQTT connection...");
 // Attempt to connect
 if (client.connect("ESP8266Client")) {
 Serial.println("connected");
 // Once connected, publish an announcement...
 client.publish("outTopic", "hello world");
 // ... and resubscribe
 client.subscribe("inTopic");
 } else {
 Serial.print("failed, rc=");
 Serial.print(client.state());
 Serial.println(" try again in 5 seconds");
 // Wait 5 seconds before retrying
 delay(1000);
 }
 }
}
void loop() {
 if (!client.connected()) {
 reconnect();
 }
 client.loop();
 long now = millis();
 if (now - lastMsg > 2000) {
 lastMsg = now;
 ++value;
 snprintf (msg, 75, "hello world #%ld", value);
 Serial.print("Publish message: ");
 Serial.println(msg);
 client.publish("outTopic", msg);
 }
}

Note: The brokers are running, I can even connect it through MQTT Box (attached picture).

MQTT Box connection

Answer 1

127.0.0.1 is not the address of your computer. That is the address of the "loopback" interface - a virtual interface that allows a device to talk to itself.

That means that when you are using the MQTT server itself you can connect, because it's all the same computer. However the ESP8266 is trying to connect to itself, not the MQTT server.

You need to replace 127.0.0.1 with the actual IP address of your MQTT server.

The simplest way of getting your computer's IP address is to open a terminal window and type:

hostname -I

• Adis Azhar: Thank you for responding. Where can I find the actual IP address of my MQTT server?
• Majenko: type ip address in a terminal and find the interface you are connecting with. It'll probably be 192.168.xxx.xxx.
• Majenko: Alternatively you can run hostname -I (that's a capital i) and it will give you all your non-loopback IP addresses.
• Adis Azhar: It returned 192.168.100.3, I have replaced it in my code, but it still shows rc = 2. Any ideas? It's only like that using local broker.
• Majenko: What IP address is your ESP8266 being given?