ESP32 Wi-Fi MAC Address Changes Unexpectedly

ESP32 Wi-Fi MAC Address Changes Unexpectedly #

If your ESP32 device shows up with a new MAC address every time it reboots, switches Wi-Fi modes, or powers on, you’re not alone. This issue can cause problems in networks that rely on static DHCP leases, MAC-based firewall rules, or device identification.

Let’s explore why this happens, how to diagnose it, and how to make your ESP32’s MAC address consistent.

Understanding ESP32 MAC Address Behavior #

The ESP32 chip comes with multiple MAC addresses:

• Wi-Fi Station (STA)
• Wi-Fi Access Point (AP)
• Bluetooth
• (Optional) Ethernet or SDIO interfaces

Each is derived from a factory-burned base MAC in EFUSE, with Espressif assigning specific offsets per interface. The key point is: the MAC can appear to change depending on which interface or mode is active.

Common Situations Where MAC Changes #

🔄 Switching Between STA and AP Mode #

If your code uses both Station and Access Point modes (WIFI_AP_STA), the reported MAC from WiFi.softAPmacAddress() and WiFi.macAddress() will differ:

Serial.println(WiFi.macAddress());      // STA MAC
Serial.println(WiFi.softAPmacAddress()); // AP MAC

These are legitimate and expected differences — but can confuse networks expecting a single MAC.

⚙️ Randomized MAC in Certain Features #

Modes like ESP-NOW, mesh, or softAP sometimes use locally-administered (randomized) MACs for privacy. This is especially true for prototyping or when no MAC is burned in EFUSE.

You may also see MACs like 02:xx:xx..., where the 02 prefix indicates a locally administered address.

🧯 MAC Set in Code (Overridden) #

Libraries or user code may call:

esp_wifi_set_mac(WIFI_IF_STA, my_mac);

This explicitly sets a MAC and will override the default. If not done consistently, the MAC will vary between boots.

Diagnosing the Issue #

To determine whether your ESP32 has a consistent factory MAC:

uint8_t base_mac[6];
esp_efuse_mac_get_default(base_mac);
Serial.printf("Base MAC: %02X:%02X:%02X:%02X:%02X:%02X\n",
  base_mac[0], base_mac[1], base_mac[2], base_mac[3], base_mac[4], base_mac[5]);

If this base MAC remains constant, your chip has a proper burned-in address.

If it’s all zeros or the call fails, you may be using a custom or engineering sample chip without a valid EFUSE MAC.

Best Practices for Stable MAC Address #

✅ Always Use STA MAC for Identification #

When using the ESP32 in client mode, get the MAC via:

WiFi.macAddress();

or

esp_wifi_get_mac(WIFI_IF_STA, mac_buffer);

This ensures consistent reporting across reboots.

✅ Avoid Switching Wi-Fi Modes Mid-Session #

Switching between STA and AP modes may change the visible MAC. If stability is needed, stick to WIFI_STA only.

✅ Assign a Manual MAC (Advanced) #

If your module lacks an EFUSE MAC or you're building pre-production hardware, you can set your own MAC using:

esp_base_mac_addr_set(my_mac);

Do this early in setup(), before Wi-Fi is initialized.

Ensure the MAC follows valid format rules — avoid multicast/reserved addresses and make it unique.

✅ Burn MAC Address in EFUSE (Manufacturing Only) #

For commercial products, Espressif recommends burning a permanent MAC into EFUSE. This requires access to the programming tools and should be done with caution.

Conclusion #

An ESP32 changing MAC addresses isn’t necessarily a bug — but it can be a headache if you’re relying on it for network tracking or static IP assignment.

To avoid surprises:

• Use the STA MAC consistently

• Don’t mix Wi-Fi modes unless needed

• Avoid libraries that override MAC unless you understand why

• Use esp_base_mac_addr_set() only if you know what you’re doing

With the right handling, you can ensure the ESP32 is reliably identified every time it connects.