ESP32 does not answer ARP requests

[edalongeville]

Hardware:

Board: ESP32 Dev Module
Core Installation version: 1.0.1
IDE name: Arduino IDE
Flash Frequency: 80Mhz
PSRAM enabled: no
Upload Speed: 115200
Computer OS: Ubuntu

Description:

The ESP32 dos not answer ARP requests.

At startup, the ESP32 sends a gratuitous ARP.
Once ESP32 startup is complete, I flush the arp cache on my Ubuntu machine (sudo ip -s -s neigh flush all) and attempt to ping the ESP32. The ARP requests sent by my machine are left unanswered.

I suspect this is a known issue, as the ESP32 sends gratuitous ARP about once per minute. This works as a temporary workaround, but in some applications, ARP requests need to be answered.

Sketch: (leave the backquotes for code formatting)

//Change the code below by your sketch
#include <WiFi.h>
#include <aREST.h>


// WiFi parameters
String ssid = "MYSSID";
String password= "MYPASSWORD";

#pragma region aRESTandWiFi

// The port to listen for incoming TCP connections
#define LISTEN_PORT           80
// Create an instance of the server
WiFiServer server(LISTEN_PORT);


void setup(void)
{


  // Start Serial
  Serial.begin(115200);

  delay(5000);

  // Connect to WiFi
  Serial.print("Connecting to wifi with ssid/password: " + ssid + "/" + password);
  WiFi.begin(ssid.c_str(), password.c_str());
  while (WiFi.status() != WL_CONNECTED) {
     delay(500);
     //write_to_logs("...");
  }
  Serial.print("WiFi connected");
  Serial.print("\n");
  Serial.print(WiFi.localIP()); // Print the IP address
  Serial.print("\n");

  }

void loop() {
  }

Debug Messages:

Connecting to wifi with ssid/password: MYSSID/MYPASSWORD[D][WiFiGeneric.cpp:342] _eventCallback(): Event: 0 - WIFI_READY
[D][WiFiGeneric.cpp:342] _eventCallback(): Event: 2 - STA_START
[D][WiFiGeneric.cpp:342] _eventCallback(): Event: 4 - STA_CONNECTED
[D][WiFiGeneric.cpp:342] _eventCallback(): Event: 7 - STA_GOT_IP
[D][WiFiGeneric.cpp:385] _eventCallback(): STA IP: 192.168.1.39, MASK: 255.255.255.0, GW: 192.168.1.1
WiFi connected
192.168.1.39 

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This stale issue has been automatically closed. Thank you for your contributions.

[szundi]

Hello, this stale bot is silly. This is a problem for me too in 2020. Stale closed tickets don't fix themselves.

[lbernstone]

By default, the esp32 runs in power save mode, where it lets the router queue up requests and only sends periodic beacon signals. To turn it off, you can do WiFi.setSleep(false);. I don't know if that will fix this, but it might.

[nopnop2002]

This issues is very similar to the one below.

esp8266/Arduino#6886

It can occur on certain routers such as Mikrotik and Fritzbox.

It doesn't happen on my router.

[vito45h]

I have run in to a similar issue, for me my ESP32 is trying to send a UDP packet to a specific IP address.

I have a wireshark on my computer where i can see the ESP32 broadcasting an arp request and instantly the computer sends back a direct arp, as seen in the following screenshot

At this point the ESP32 can't be ping from the computer, it seems the only way to get it working again is to power cycle it.

[jnwatts]

I've been struggling with this for weeks: My ESP is acting as a server, and my clients would sometimes work just fine, and other times take up to a minute (usually timing out) to get a response from the ESP. The issue is not a failure to respond to ARP, it's that the wifi-modem is in low power by default!!

The only reason my clients ever managed to work, was due to the default gratuitous arp frequency of 60 seconds: Client would issue ARP request, and IF a G-ARP happens within the connect-timeout period, then the connection would succeed and all is well.

Unfortunately, I'm not sure how/where to set this for arduino-esp32, as I switched over to esp-idf. In the idf API, the solution is to turn of wifi-modem sleep:

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/sleep_modes.html

ESP_ERROR_CHECK(esp_wifi_set_ps(WIFI_PS_NONE));

[lbernstone]

WiFi.setSleep(false);