Getting DHCP options using ESP32

Question

I've dealing with an ESP32 module (ESP-IDF) trying to connect via Wifi and ethernet to a dhcp server. The point is, I'm trying to get the DHCP options, but I failed...

I tried using LWIP and also ESP-NETIF. (I have also to guess whats XXXX and YYYY)

// Create an esp_netif pointer to store current interface
  esp_netif_t* ifscan = esp_netif_next(NULL);

  // Stores the unique interface descriptor, such as "PP1", etc
  char ifdesc[7];
  ifdesc[6] = 0;  // Ensure null terminated string
  uint32_t value = 0;

  while (ifscan != NULL)
  {
      esp_netif_get_netif_impl_name(ifscan, ifdesc);
      Serial.printf("IF NAME: %s\n", ifdesc);

      esp_err_t code = esp_netif_dhcpc_option(ifscan, ESP_NETIF_OP_GET, ESP_NETIF_DOMAIN_NAME_SERVER, XXXX, YYYY);
      Serial.printf("RES: %s - OPTION: %s\n", esp_err_to_name(code), XXXXX);
   


      // Get the next interface
      ifscan = esp_netif_next(ifscan);
  }
      Serial.printf("Done listing network interfaces");

Does anyone have an example of sourcecode showing how to get the options after connecting?

Thank you in advance.

MadddinTribleD · Accepted Answer · 2022-06-19 16:19:04Z

There are only a couple of DHCP options implemented in code.
Check the source code (github) for esp_netif_dhcpc_option.
ESP_NETIF_DOMAIN_NAME_SERVER e.q. is not.

For ESP_NETIF_OP_GET there is only ESP_NETIF_IP_REQUEST_RETRY_TIME and ESP_NETIF_VENDOR_SPECIFIC_INFO implemented.
Otherwise you get ESP_ERR_ESP_NETIF_INVALID_PARAMS (20481 0x5001) as a result.

esp_err_t esp_netif_dhcpc_option(esp_netif_t *esp_netif, esp_netif_dhcp_option_mode_t opt_op, esp_netif_dhcp_option_id_t opt_id, void *opt_val,
                                 uint32_t opt_len)
{
...
    if (opt_op == ESP_NETIF_OP_GET) {
        if (esp_netif->dhcpc_status == ESP_NETIF_DHCP_STOPPED) {
            return ESP_ERR_ESP_NETIF_DHCP_ALREADY_STOPPED;
        }
        switch (opt_id) {
            case ESP_NETIF_IP_REQUEST_RETRY_TIME:
                if (opt_len == sizeof(dhcp->tries)) {
                    *(uint8_t *)opt_val = dhcp->tries;
                }
                break;
#if ESP_DHCP && !ESP_DHCP_DISABLE_VENDOR_CLASS_IDENTIFIER
            case ESP_NETIF_VENDOR_SPECIFIC_INFO:
                return dhcp_get_vendor_specific_information(opt_len, opt_val);
#endif
            default:
                return ESP_ERR_ESP_NETIF_INVALID_PARAMS;
        }
...
}

I tried with your code and option 224 on my ESP32

  Serial.println("Option >");
  esp_err_t result = 0;
  uint32_t value = 0;
  esp_netif_t * ifscan = esp_netif_next(NULL);
  char ifname[10];
  result = esp_netif_get_netif_impl_name(ifscan, ifname);
  Serial.print("esp_netif_get_netif_impl_name: ");
  Serial.println(result);
  result = esp_netif_dhcpc_option(ifscan, ESP_NETIF_OP_GET, (esp_netif_dhcp_option_id_t)224, &value, 4);
  Serial.print("esp_netif_dhcpc_option: ");
  Serial.println(result);
  Serial.print("esp_netif_dhcpc_option value: ");
  Serial.println(value);
  Serial.println("Option <");

Result:

Option >
esp_netif_get_netif_impl_name: 0
esp_netif_dhcpc_option: 20481
esp_netif_dhcpc_option value: 0
Option <

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