Forum: µC & Digital Electronics ESP8266 "calling home"

Author: Jo (Guest)
Posted on:
Attached files:

Rate this post
0 useful
not useful
NOTE: This is a translation of my German post 'ESP8266 "telefoniert nach 
Hause"' in mikrocontroller.net. I translated it to reach a broader and 
more international audience.

Back in october/november I build a light sensor to control the lighting 
around my house. You can see the result in the attached picture and the 
sensor works fine. The ESP8266 is connected to a WLAN, that is not 
connected to the internet and is utilized only for local traffic. Then I 
got a new router and noticed, that the ESP8266 tries to reach an 
external IP address (now, two weeks ago it was The ESP8266 scans ports in the upper port range from 
about port 30.000 to 62.000 on that specific address.

Until I noticed the described behaviour, the ESP8266 was not capable to 
communicate with external (internet) IP addresses. I can rule out that 
the ESP8266 responds to incoming traffic from the internet. I changed 
that now and currently I am sniffing the traffic. An actual log of this 
traffic is attached as a PCAP-File, which you can download for the use 
in Wireshark.

My device is an ESP8266 coupled with an I2C BH1750 light sensor. The 
ESP8266 contains portions of the „ESP8266AdvancedWebserver“ example of 
the Aruino IDE (1.6.4) plugin, which was installed through the 
board-manager. The webserver returns the sensor value upon a http 

I have coded the ESP myself via Arduino IDE and scanned the libs 
available as source code. I did not find anything that could explain the 

I have made use of the following libs:

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

At the moment I cannot re-enact this situation in lab conditions and 
with different releases. Hence, I kindly ask you to check if your 
ESP8266 is calling home as well. You just need to check the routing 
table of your router.

Please post if your ESP8266 connects to "alien" servers as well. 
Positive/negative reports are welcome.

I attached a picture of my light-sensor, screenshots of my routing table 
and a pcap file for Wireshark, where I have collected a few of the 
suspicous pakets.

I look forward to hearing from you,

Author: stefan us (Guest)
Posted on:

Rate this post
0 useful
not useful
It turned out that the issue was caused by the application itself (not 
the ESP module or firmware).  What seemed like "calling home" are really 
random data.


Entering an e-mail address is optional. If you want to receive reply notifications by e-mail, please log in.

Rules — please read before posting

  • Post long source code as attachment, not in the text
  • Posting advertisements is forbidden.

Formatting options

  • [c]C code[/c]
  • [avrasm]AVR assembler code[/avrasm]
  • [code]code in other languages, ASCII drawings[/code]
  • [math]formula (LaTeX syntax)[/math]

Bild automatisch verkleinern, falls nötig
Note: the original post is older than 6 months. Please don't ask any new questions in this thread, but start a new one.