5. FAQ

5.1. Can’t ping the Wi-Fi device using the OT CLI ping command

The Espressif Thread Border Router (BR) framework integrates the OpenThread stack and the Wi-Fi stack as network interfaces (Netif) connected to lwIP, with both OpenThread and Wi-Fi addresses managed by lwIP.

-----------                                          ------------
|         |                                          |   lwIP   |
|         |                                          |   -----  |
|         |                                          |   |   |  |
|  Wi-Fi  |                                          |-↑-↓---↑--|
|  Device | <--- Ping Request to Wi-Fi Device ------ | |   | |  |
|         | ----------- Ping Reply to BR ----------> |-|   | |--|<---- Ping command is
|         |                                          | WiFi| OT |      generated at the OT layer
|         |                                          |     |    |
-----------                                          ------------

lwIP serves as the upper layer for both OpenThread and Wi-Fi, handling packet forwarding between network interfaces. Here is how it works in this setup:

  1. The ping command is generated at the OpenThread layer, and the ping packet is sent to lwIP for forwarding.

  2. lwIP recognizes that the destination address belongs to the Wi-Fi Netif and forwards the packet to the Wi-Fi interface.

  3. The peer Wi-Fi device receives the ping packet and sends a reply back to the BR.

  4. The BR receives the reply packet on the Wi-Fi interface and forwards it to lwIP for processing.

  5. lwIP identifies that the destination address is assigned to the BR itself (since OpenThread assigns the OMR address to lwIP). Because of this, lwIP does not forward the reply packet back to the OpenThread layer.

  6. Since the OpenThread layer does not receive the reply packet, it incorrectly shows the ping response as lost, even though the BR successfully receives the reply.

To see a successful ping reply from the Wi-Fi device to BR, you need to implement the ping command at the lwIP layer instead. This allows you to directly ping the Wi-Fi device from lwIP, bypassing the OpenThread stack.

5.2. Host SoC can’t communicate with RCP properly

If you set up the BR using standalone modules manually, please update the GPIO pin configurations (radio_uart_config) in esp_ot_config.h for both the ot_rcp and BR examples to accurately reflect the GPIO connections between the Wi-Fi and 802.15.4 SoCs.

The Host and RCP will be unable to communicate if the communication interface is not configured correctly, resulting in warning logs similar to the following:

W(2499) OPENTHREAD:[W] P-SpinelDrive-: Wait for response timeout

Note

GPIO17 and GPIO18 on the ESP32-S3 have a different driver current (refer to ESP32-S3 TRM, Chapter 6.12). If an ESP32-S3 is used as the host, GPIO4 and GPIO5 are recommended for use as the UART RX/TX GPIOs.

5.3. Using ot_rcp with OTBR (ot-br-posix)

The OpenThread Border Router (OTBR) is a Linux-based Thread BR solution. Setup instructions can be found here: OpenThread Border Router Build and Configuration.

The ESP Thread RCP (ot_rcp) can also function as the RCP in an OTBR setup. However, the otbr-agent configuration needs to be adjusted accordingly:

  • The default otbr-agent configuration uses /dev/ttyACM0. Each ESP devkit has two ports:

    • A USB port, recognized as /dev/ttyACMx

    • A UART port, recognized as /dev/ttyUSBx

  • The default baudrate in otbr-agent` is 115200, while the default baudrate in (ot_rcp) example is 460800

Please refer to Step 4 in ` OpenThread Border Router Build and Configuration <https://openthread.io/guides/border-router/build#attach-and-configure-rcp-device>`_ and update the UART configuration to use the correct USB port number (i.e. replace /dev/ttyUSB0 with /dev/ttyUSBx) and baud rate in the otbr-agent configuration file /etc/default/otbr-agent:

OTBR_AGENT_OPTS="-I wpan0 -B wlan0 spinel+hdlc+uart:///dev/ttyUSB0?uart-baudrate=460800"

Restart the otbr-agent service, and confirm it works with the RCP now:

➜ sudo service otbr-agent status
● otbr-agent.service - OpenThread Border Router Agent
  Loaded: loaded (/lib/systemd/system/otbr-agent.service; enabled; vendor preset: enabled)
  Active: active (running) since Fri 2025-02-28 17:45:20 CST; 29min ago
  Process: 1160169 ExecStartPre=/usr/sbin/service mdns start (code=exited, status=0/SUCCESS)
  Main PID: 1160178 (otbr-agent)
   Tasks: 1 (limit: 18871)
  Memory: 920.0K
     CPU: 395ms
  CGroup: /system.slice/otbr-agent.service
          └─1160178 /usr/sbin/otbr-agent -I wpan0 -B wlx0013eff10f89 "spinel+hdlc+uart:///dev/ttyUSB0?uart-baudrate=460800" trel://wlx0013eff10f89

Feb 28 18:13:05 madcow-OptiPlex-3070 otbr-agent[1160178]: 00:27:44.764 [I] MeshForwarder-:     dst:[ff02:0:0:0:0:0:0:1]:19788
Feb 28 18:13:10 madcow-OptiPlex-3070 otbr-agent[1160178]: 00:27:49.324 [I] MeshForwarder-: Received IPv6 UDP msg, len:83, chksum:8c92, ecn:no, from:3618183b10a40a22, sec:no, prio:net, rss:-70.0