ESP32 Forum

Posted: **Tue May 10, 2022 5:00 pm**

I'm trying to fix several issues related to DHCP, and I'm really struggling with the scarce documentation.

Does anyone know where to find documentation for this function? The opt_val parameter is critical, but I can't find any documentation for it.

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esp_err_t esp_netif_dhcpc_option(esp_netif_t *esp_netif, esp_netif_dhcp_option_mode_topt_op, esp_netif_dhcp_option_id_topt_id, void *opt_val, uint32_t opt_len)

The parameters of the function are described, and I can look up what options there are in the first structs. I think I want:

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esp_netif_dhcps_option(netIfInstancePtr
			, ESP_NETIF_OP_SET
			, ESP_NETIF_DOMAIN_NAME_SERVER
			, void* opt_val
			, uint32_t opt_len);

Could someone please point me in the right direction? What goes into opt_val?

Posted: **Wed May 11, 2022 2:04 am**

The opt_val is a void type pointer. It can be input or output data depend on opt_op is GET or SET.
For example, if you want to set dhcp->tries， you can follow this code:

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uint8_t tries;
uint32_t len = sizeof(tries);
esp_netif_dhcpc_option(esp_netif, ESP_NETIF_OP_SET, ESP_NETIF_IP_REQUEST_RETRY_TIME, &tries, len);

Posted: **Wed May 11, 2022 6:38 pm**

Thanks, I'm with you thus far. But how can I know what the pointer is supposed to point to?

Here are all the valid options:

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typedef enum{
    ESP_NETIF_SUBNET_MASK                   = 1,    /**< Network mask */
    ESP_NETIF_DOMAIN_NAME_SERVER            = 6,    /**< Domain name server */
    ESP_NETIF_ROUTER_SOLICITATION_ADDRESS   = 32,   /**< Solicitation router address */
    ESP_NETIF_REQUESTED_IP_ADDRESS          = 50,   /**< Request specific IP address */
    ESP_NETIF_IP_ADDRESS_LEASE_TIME         = 51,   /**< Request IP address lease time */
    ESP_NETIF_IP_REQUEST_RETRY_TIME         = 52,   /**< Request IP address retry counter */
    ESP_NETIF_VENDOR_CLASS_IDENTIFIER       = 60,   /**< Vendor Class Identifier of a DHCP client */
    ESP_NETIF_VENDOR_SPECIFIC_INFO          = 43,   /**< Vendor Specific Information of a DHCP server */
} esp_netif_dhcp_option_id_t;

You are saying that for ESP_NETIF_IP_REQUEST_RETRY_TIME, opt_val is a pointer to one byte of uint8_t. But some of the others are IP addresses that are probably represented by one uint32_t. How do we know which one?

Specifically, in the case of ESP_NETIF_DOMAIN_NAME_SERVER, what is the opt_val? A 32-bit IP or something else?

Thanks

Posted: **Thu May 12, 2022 2:02 am**

The ESP_NETIF_DOMAIN_NAME_SERVER is in https://github.com/espressif/esp-idf/bl ... ip.c#L1808 and you can see the opt_val is uint8_t.

Posted: **Wed Jul 12, 2023 10:17 pm**

ldudel wrote: ↑
Wed May 11, 2022 6:38 pm
Thanks, I'm with you thus far. But how can I know what the pointer is supposed to point to?

Here are all the valid options:
Code: Select all
typedef enum{
    ESP_NETIF_SUBNET_MASK                   = 1,    /**< Network mask */
    ESP_NETIF_DOMAIN_NAME_SERVER            = 6,    /**< Domain name server */
    ESP_NETIF_ROUTER_SOLICITATION_ADDRESS   = 32,   /**< Solicitation router address */
    ESP_NETIF_REQUESTED_IP_ADDRESS          = 50,   /**< Request specific IP address */
    ESP_NETIF_IP_ADDRESS_LEASE_TIME         = 51,   /**< Request IP address lease time */
    ESP_NETIF_IP_REQUEST_RETRY_TIME         = 52,   /**< Request IP address retry counter */
    ESP_NETIF_VENDOR_CLASS_IDENTIFIER       = 60,   /**< Vendor Class Identifier of a DHCP client */
    ESP_NETIF_VENDOR_SPECIFIC_INFO          = 43,   /**< Vendor Specific Information of a DHCP server */
} esp_netif_dhcp_option_id_t;
You are saying that for ESP_NETIF_IP_REQUEST_RETRY_TIME, opt_val is a pointer to one byte of uint8_t. But some of the others are IP addresses that are probably represented by one uint32_t. How do we know which one?

Specifically, in the case of ESP_NETIF_DOMAIN_NAME_SERVER, what is the opt_val? A 32-bit IP or something else?

Thanks

what does ESP_NETIF_ROUTER_SOLICITATION_ADDRESS = 32 even mean? This is supposed to be an ip address right? Why is it just a number. How would i change the ip to something like 192.168.1.1?

Posted: **Tue Aug 29, 2023 9:22 am**

You can use ipaddr_ntoa_r to convert it to string.

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