nRF51 IoT SDK
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The DNS client module provides the functionality for obtaining DNS AAAA (IPv6) records from the authoritative DNS server. The module performs queries for the IPv6 addresses of the given hostname (e.g. example.com).
Each query can be assigned with a separate application callback that informs about the IPv6 addresses found, DNS frame error or DNS Server problem.
The module realizes a retry mechanism to improve chances of resolving the DNS Query. The number of retries is configurable using the DNS6_MAX_RETRANSMISSION_COUNT. The interval between retries is determined by the configurable parameter DNS6_RETRANSMISSION_INTERVAL. Therefore, an application can expect to wait for ((DNS6_MAX_RETRANSMISSION_COUNT + 1) * DNS6_RETRANSMISSION_INTERVAL) before the query is resolved. If no response is received after the maximum number of retries, the application is notified of process result DNS6_SERVER_UNREACHABLE in the event notification callback.
The user DNS callback informs about the internal process result, which can be either NRF_SUCCESS or one of the following errors:
Process result | Description |
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DNS6_SERVER_UNREACHABLE | No response from the DNS Server has been received. |
DNS6_FORMAT_ERROR | The DNS Server was unable to interpret the query. |
DNS6_SERVER_FAILURE | The DNS Server was unable to process the query. |
DNS6_HOSTNAME_NOT_FOUND | No IPv6 addresses have been found. |
DNS6_NOT_IMPLEMENTED | The DNS Server does not support the requested kind of query. |
DNS6_REFUSED_ERROR | The DNS Server refuses to perform the query. |
DNS6_RESPONSE_TRUNCATED | Response from the DNS Server is truncated. |
Other | In case the DNS module is not the source of an error. |
This code example shows how to set up the DNS Client in order to send a DNS Query and receive responses. In the example below, Google's DNS Server is used.
This code example shows how to send a DNS Query for resolving the given hostname. The application is informed about the status of the DNS process in a user-defined function.
The following configuration parameters should be defined in sdk_config.h
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Disables debug tracing in the module. To enable tracing, this flag must be set to 0 and ENABLE_DEBUG_LOG_SUPPORT must be set to 1.
Description | Value |
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Enable debug trace | 0 |
Disable debug trace | 1 |
Dependencies | ENABLE_DEBUG_LOG_SUPPORT |
Disables API parameter checks in the module. Set this define to 1 to disable checks on API parameters in the module.
API parameter checks are added to ensure that the correct parameters are passed to the module. These checks are useful during development phase, but they might be redundant when the application is finalized. Disabling these checks might improve performance.
Description | Value |
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Enable API parameters check | 0 |
Disable API parameters check | 1 |
Dependencies | None |
Maximum number of pending queries in a queue.
Description | Value |
---|---|
Minimum value | 1 |
Maximum value | 65534 |
Dependencies | None |
Maximum number of retransmissions on a single query. Set this define to 0 to disable retransmission attempts.
Description | Value |
---|---|
Minimum value | 0 |
Maximum value | 255 |
Dependencies | None |
Interval between retransmissions in seconds.
Description | Value |
---|---|
Minimum value | 2 |
Maximum value | None |
Dependencies | None |