Cannot connect to GATT server using Windows 11

[ayan4m1]

I am running Windows 11 25H2. I am using the latest stable Chrome and also the OS's inbuilt Bluetooth functionality to test connecting to my ESP32 BLE server. My code:

#include <Arduino.h>
#include <FastLED.h>
#include <NimBLEDevice.h>

#define LED_COUNT 1
#define LED_PIN 48

#define IP_ADDR_SERVICE_UUID "0c3df205-d093-46ab-b360-74e67fee325f"
#define WIFI_SETUP_SERVICE_UUID "cab5bfc5-18a5-4924-bcf8-02269e00301c"
#define IP_ADDR_CHARACTERISTIC_UUID "5181caeb-8309-48e5-942f-5e678fccf4db"
#define SSID_CHARACTERISTIC_UUID "88f26ae8-04f1-49ab-9341-1208f7b0fff8"
#define PSK_CHARACTERISTIC_UUID "ad42f5f5-6560-4773-9604-925d0727c671"

NimBLEServer* bleServer;
CRGB leds[LED_COUNT];

void setup() {
  FastLED.addLeds<WS2812B, LED_PIN, GRB>(leds, LED_COUNT);
  FastLED.setBrightness(100);

  leds[0] = CRGB::Yellow;

  FastLED.show();

  NimBLEDevice::init("CT Tester");

  bleServer = NimBLEDevice::createServer();
  auto ipAddressService = bleServer->createService(IP_ADDR_SERVICE_UUID);
  auto wifiSetupService = bleServer->createService(WIFI_SETUP_SERVICE_UUID);
  auto ipCharacteristic = ipAddressService->createCharacteristic(
      IP_ADDR_CHARACTERISTIC_UUID,
      NIMBLE_PROPERTY::READ | NIMBLE_PROPERTY::WRITE | NIMBLE_PROPERTY::NOTIFY);
  auto ssidCharacteristic =
      wifiSetupService->createCharacteristic(SSID_CHARACTERISTIC_UUID);
  auto pskCharacteristic =
      wifiSetupService->createCharacteristic(PSK_CHARACTERISTIC_UUID);

  ipAddressService->start();
  wifiSetupService->start();

  ipCharacteristic->setValue("1.2.3.4");

  auto advertising = NimBLEDevice::getAdvertising();

  advertising->addServiceUUID(IP_ADDR_SERVICE_UUID);
  advertising->addServiceUUID(WIFI_SETUP_SERVICE_UUID);
  advertising->enableScanResponse(true);
  advertising->setConnectableMode(BLE_GAP_CONN_MODE_UND);
  advertising->setName("CT Tester");
  advertising->start();

  bleServer->start();

  leds[0] = CRGB::Green;

  FastLED.show();
}

void loop() {}

The LED goes green on startup, and the device is adveritising. However, any connection attempt times out with a failure (error code 0 in Chrome). I have tried with and without the setConnectableMode call.

[h2zero]

If im not mistaken I don't think windows will connect to a device that doesn't have bonding enabled.

[axa88]

If im not mistaken I don't think windows will connect to a device that doesn't have bonding enabled.

I'm absolutely sure a BLE client using the windows SDK can allow a connection without having a bond.
Im unsure how "Chrome" in this case, affects the use of the underlying windows sdk but, targeting:

<TargetFramework>net10.0-windows10.0.26100.0</TargetFramework>

and most likely earlier versions, will allow it as per spec, fwiw I do it all the time.

Probably already done it, but i'd advise trying with another client like nRF Connect, and confirm your peripheral is working as expected.

[afpineda]

This seems to be an specific issue with Windows 11 2025H2 (not other versions).
This is how I fixed it:

Go to Settings > System > Recovery > Fix problems using Windows Update > Reinstall now.

[afpineda]

If im not mistaken I don't think windows will connect to a device that doesn't have bonding enabled.

Not exactly and not only Windows.
Just HID devices.
You can connect HID devices without pairing, but bonding is required for the operating system to reroute HID reports to all applications.

[ayan4m1]

This seems to be an specific issue with Windows 11 2025H2 (not other versions). This is how I fixed it:

Go to Settings > System > Recovery > Fix problems using Windows Update > Reinstall now.

Sorry, I'm not reinstalling my entire copy of Windows to fix this. That's very disappointing. Thanks.

[afpineda]

Sorry, I'm not reinstalling my entire copy of Windows to fix this. That's very disappointing. Thanks.

That's not a reinstall, but another patch. It takes less than an hour and is not destructive.

[axa88]

If I'm not mistaken I don't think windows will connect to a device that doesn't have bonding enabled.

I should clarify. while I'm confident connection is possible without bonding, this is of course only relevant if both devices agree to not to ask/require a bond upon connection or data exchange. Confirm your client doesn't attempt to pair and hang as you're not handling the request.
To do this , you could simply set with a NimBLEServerCallbacks and verify the device isn't requesting authenticated pair and you're not handling it.

Edit: just ran some test with this library, indeed a bond is not needed to connect.