---
product: Chilkat
product_version: 11.7.0
language: csharp
language_label: C#
class: Dns
license: bundle
deprecated: false
reference_html: https://www.chilkatsoft.com/refdoc/csDnsRef.html
---
# Chilkat Dns — C# — v11.7.0

> Chilkat 11.7.0 · language=csharp · class=Dns
> Other versions: replace `11.7.0` in this URL. Other languages: `https://www.chilkatsoft.com/ai-docs/v/11.7.0/<lang>/classes/Dns.md`.
> Language-wide rules (install, unlock, error model, strings/bytes): `https://www.chilkatsoft.com/ai-docs/v/11.7.0/csharp/guide.md`.

## Purpose

**Configure DNS resolution and query DNS records directly from Chilkat.**

`Chilkat.Dns` is a focused class for DNS configuration and DNS record querying. It allows applications to control the nameservers used by Chilkat, query common DNS record types into JSON, configure DNS-over-TLS preference, set DNS query timeouts, and obtain useful diagnostics through `LastErrorText`.

**DNS record queries**

Query common DNS record types and receive structured JSON results that are easy to inspect or pass to other application logic.

**Nameserver control**

Configure the nameservers Chilkat uses instead of relying only on the operating system's default DNS configuration.

**DNS-over-TLS preference**

Prefer DNS-over-TLS when appropriate for applications that need encrypted DNS lookups.

**Timeout settings**

Control how long DNS queries may wait before failing, which is useful for responsive applications and troubleshooting.

**Application-wide behavior**

Nameserver settings affect DNS resolution across Chilkat classes, not only the current `Dns` object.

**Diagnostics**

Use `LastErrorText` to troubleshoot DNS configuration, lookup failures, timeout problems, or nameserver connectivity issues.

**Common pattern:** Use `Dns` either to perform direct DNS lookups, or to configure the DNS behavior used by Chilkat as a whole. Because nameserver changes can affect DNS resolution across Chilkat classes, treat them as application-wide configuration rather than object-local state.

For an extended overview, see [Dns Class Overview](https://www.chilkatsoft.com/dns_class_overview.asp).

## Object creation, unlocking and error handling

**Object Creation**

```csharp
Chilkat.Dns obj = new Chilkat.Dns();
```

Call `Global.UnlockBundle` once at the start of the program, before using this or any other Chilkat class. Any string unlocks a fully functional 30-day trial; a purchased unlock code is used in production. See `guide.md` for the exact code in C#.

Minimal complete program:

```csharp
// Required once per process. Any string unlocks a 30-day trial; use your purchased code in production.
Chilkat.Global glob = new Chilkat.Global();
if (!glob.UnlockBundle("Anything for 30-day trial"))
{
    Console.WriteLine(glob.LastErrorText);
    return;
}

Chilkat.Dns dns = new Chilkat.Dns();
```

How failure is reported depends on the method's return type and is stated in the note under each method below. In every case the diagnostic text is in the `LastErrorText` property of the object whose method was called.

## Members common to every Chilkat class

Documented once per language in `common-members.md`; listed here so this page is self-contained.

| Property | Signature | Access | Meaning |
|---|---|---|---|
| `DebugLogFilePath` | `public string DebugLogFilePath {get; set; }` | read/write | If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. |
| `LastErrorHtml` | `public string LastErrorHtml {get; }` | read-only | Provides HTML-formatted information about the last called method or property. |
| `LastErrorText` | `public string LastErrorText {get; }` | read-only | Provides plain text information about the last called method or property. |
| `LastErrorXml` | `public string LastErrorXml {get; }` | read-only | Provides XML-formatted information about the last called method or property. |
| `LastMethodSuccess` | `public bool LastMethodSuccess {get; set; }` | read/write | Indicates the success or failure of the most recent method call: `true` means success, `false` means failure. |
| `VerboseLogging` | `public bool VerboseLogging {get; set; }` | read/write | If set to `true`, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. |
| `Version` | `public string Version {get; }` | read-only | Version of the component/library, such as "10.1.0" |

## Member index

| Member | Kind | Signature |
|---|---|---|
| `HeartbeatMs` | property, read/write | `public int HeartbeatMs {get; set; }` |
| `MaxWaitMs` | property, read/write | `public int MaxWaitMs {get; set; }` |
| `NumNameservers` | property, read-only | `public int NumNameservers {get; }` |
| `TlsPref` | property, read/write | `public int TlsPref {get; set; }` |
| `UncommonOptions` | property, read/write | `public string UncommonOptions {get; set; }` |
| `AddDefaultNameservers` | method | `public void AddDefaultNameservers();` |
| `AddNameserver` | method | `public void AddNameserver(string ipAddr, bool supportsTls);` |
| `GetNameserver` | method | `public string GetNameserver(int index);` |
| `Query` | method | `public bool Query(string recordType, string domain, JsonObject answer);` |
| `RemoveAllNameservers` | method | `public void RemoveAllNameservers();` |
| `RemoveNameserver` | method | `public void RemoveNameserver(string ipAddr);` |

## Properties

### Dns.HeartbeatMs

`Chilkat 11.7.0 · csharp · Dns · HeartbeatMs · property · read/write · since 9.5.0.96`

```csharp
public int HeartbeatMs {get; set; }
```

**Full documentation for this property (same in every language):** [Event Callback Examples](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/event_callback_examples.md)

The interval in milliseconds between each `AbortCheck` event callback, which enables an application to abort certain method calls before they complete. **By default, HeartbeatMs is set to** `0`**, meaning no AbortCheck event callbacks will trigger.**

### Dns.MaxWaitMs

`Chilkat 11.7.0 · csharp · Dns · MaxWaitMs · property · read/write · since 9.5.0.96`

```csharp
public int MaxWaitMs {get; set; }
```

The maxiumum number of milliseconds to wait for the answer to a DNS query. A value of 0 is to wait indefinitely (no timeout). It's not a good idea to specify 0 (infinite timeout) or a value less than 1000 (1 second). The default value is 10000 milliseconds.

### Dns.NumNameservers

`Chilkat 11.7.0 · csharp · Dns · NumNameservers · property · read-only · since 9.5.0.96`

```csharp
public int NumNameservers {get; }
```

The number of nameservers currently being used by Chilkat for DNS queries in all objects/classes, such as for HTTP, Email, FTP, SSH, etc.

### Dns.TlsPref

`Chilkat 11.7.0 · csharp · Dns · TlsPref · property · read/write · since 9.5.0.96`

```csharp
public int TlsPref {get; set; }
```

Specifies the TLS preference. Possible values are:

- 0 = No TLS
- 1 = Prefer TLS if possible.
- 2 = Require TLS

The default value is 0. If TLS is preferred then DNS nameservers with TLS capability will be tried first. If none succeed, then UDP/TCP will be tried. If TLS is required, then only TLS capable nameservers will be tried and all DNS queries will use TLS.

Note: To use TLS, your application needs to first specify nameservers by calling AddNameserver once per nameserver with the supportsTls argument set to `true`.

### Dns.UncommonOptions

`Chilkat 11.7.0 · csharp · Dns · UncommonOptions · property · read/write · since 11.4.0`

```csharp
public string UncommonOptions {get; set; }
```

This is a catch-all property to be used for uncommon needs. This property defaults to the empty string and should typically remain empty.

## Methods

### Dns.AddDefaultNameservers

`Chilkat 11.7.0 · csharp · Dns · AddDefaultNameservers · method · since 9.5.0.96`

```csharp
public void AddDefaultNameservers();
```

Adds the default (auto-assigned) nameservers to the collection of nameservers used by Chilkat for DNS queries and domain to IP address lookups.

### Dns.AddNameserver

`Chilkat 11.7.0 · csharp · Dns · AddNameserver · method · since 9.5.0.96`

```csharp
public void AddNameserver(string ipAddr, bool supportsTls);
```

Adds a new nameserver to the collection of nameservers used by Chilkat for DNS queries and domain to IP address lookups. The `ipAddr` specifies the IPv4 address of the nameserver. The `supportsTls` indicates if the namserver supports DoT (DNS over TLS. DoT uses port 853 for encrypted DNS communication.) If the TlsPreference property is set to 1 or 2, then Chilkat will use TLS nameservers.

### Dns.GetNameserver

`Chilkat 11.7.0 · csharp · Dns · GetNameserver · method · since 9.5.0.96`

```csharp
public string GetNameserver(int index);
```

Returns the IP address of the Nth nameserver currently used by Chilkat for DNS queries and domain to IP address lookups. The `index` specifies the index of the nameserver. The 1st nameserver is at `index` 0.

Returns `null` on failure

### Dns.Query

`Chilkat 11.7.0 · csharp · Dns · Query · method · since 9.5.0.96`

```csharp
public bool Query(string recordType, string domain, JsonObject answer);
```

Performs an DNS query for `domain` and returns the answer in `answer`. The type of DNS query is specified in `recordType` and can be A, AAAA, ALIAS, CAA, MX, NS, SOA, TXT. Additional record types can be added as needed.

Async variant: `QueryAsync` — same arguments, returns a `Task` (see Async variants below).

### Dns.RemoveAllNameservers

`Chilkat 11.7.0 · csharp · Dns · RemoveAllNameservers · method · since 9.5.0.96`

```csharp
public void RemoveAllNameservers();
```

Removes all nameservers from the collection of nameservers used by Chilkat. An application can call this method to reset to 0 nameservers before adding new nameservers. If a DNS domain to IP address resolution is needed by Chilkat, then the auto-assigned nameserver IP addresses will be automaticaly restored.

### Dns.RemoveNameserver

`Chilkat 11.7.0 · csharp · Dns · RemoveNameserver · method · since 9.5.0.96`

```csharp
public void RemoveNameserver(string ipAddr);
```

Removes a nameserver from the collection of nameservers used by Chilkat. The `ipAddr` is the IPv4 address of the nameserver to be removed.

## Events and callbacks

### Dns.AbortCheck (event)

`Chilkat 11.7.0 · csharp · Dns · AbortCheck · event`

```csharp
public event AbortCheckEventHandler OnAbortCheck;
```

Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the `HeartbeatMs` property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.

### Chilkat .NET Framework Event Implementation

Args are passed using Chilkat.AbortCheckEventArgs

**Event callback implementation:**

```csharp
private void dns_OnAbortCheck(object sender, Chilkat.AbortCheckEventArgs args)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
dns.OnAbortCheck += dns_OnAbortCheck;
```

### Chilkat .NET Core Event Implementation

**Event callback implementation:**

```csharp
public void handleAbortCheck(out bool abort)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
// ...
Chilkat.Dns.AbortCheck abortCheck = new Chilkat.Dns.AbortCheck(handleAbortCheck);
dns.setAbortCheckCb(abortCheck);
```

### Dns.PercentDone (event)

`Chilkat 11.7.0 · csharp · Dns · PercentDone · event`

```csharp
public event PercentDoneEventHandler OnPercentDone;
```

This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The `pctDone` argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have `pctDone` equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).

The PercentDone callback also acts as an `AbortCheck` event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.

To abort the operation, set the `abort` output argument to `true`. This will cause the method to terminate and return a failure status or corresponding failure value.

### Chilkat .NET Framework Event Implementation

Args are passed using Chilkat.PercentDoneEventArgs

**Event callback implementation:**

```csharp
private void dns_OnPercentDone(object sender, Chilkat.PercentDoneEventArgs args)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
dns.OnPercentDone += dns_OnPercentDone;
```

### Chilkat .NET Core Event Implementation

**Event callback implementation:**

```csharp
public void handlePercentDone(int pctDone, out bool abort)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
// ...
Chilkat.Dns.PercentDone percentDone = new Chilkat.Dns.PercentDone(handlePercentDone);
dns.setPercentDoneCb(percentDone);
```

### Dns.ProgressInfo (event)

`Chilkat 11.7.0 · csharp · Dns · ProgressInfo · event`

```csharp
public event ProgressInfoEventHandler OnProgressInfo;
```

This event callback provides `tag name`/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.

Note: Some Chilkat methods don't fire any ProgressInfo events.

### Chilkat .NET Framework Event Implementation

Args are passed using Chilkat.ProgressInfoEventArgs

**Event callback implementation:**

```csharp
private void dns_OnProgressInfo(object sender, Chilkat.ProgressInfoEventArgs args)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
dns.OnProgressInfo += dns_OnProgressInfo;
```

### Chilkat .NET Core Event Implementation

**Event callback implementation:**

```csharp
public void handleProgressInfo(string name, string value)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
// ...
Chilkat.Dns.ProgressInfo progressInfo = new Chilkat.Dns.ProgressInfo(handleProgressInfo);
dns.setProgressInfoCb(progressInfo);
```

### Dns.TaskCompleted (event)

`Chilkat 11.7.0 · csharp · Dns · TaskCompleted · event`

```csharp
public event TaskCompletedEventHandler OnTaskCompleted;
```

Called from the background thread when an asynchronous task completes.

### Chilkat .NET Framework Event Implementation

Args are passed using Chilkat.TaskCompletedEventArgs

**Event callback implementation:**

```csharp
private void dns_OnTaskCompleted(object sender, Chilkat.TaskCompletedEventArgs args)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
dns.OnTaskCompleted += dns_OnTaskCompleted;
```

### Chilkat .NET Core Event Implementation

**Event callback implementation:**

```csharp
public void handleTaskIdCompleted(int taskId)
	{
	    // application code goes here.
	}
```

**To add an event handler:**

```csharp
Chilkat.Dns dns = new Chilkat.Dns();
// ...
Chilkat.Dns.TaskIdCompleted taskIdCompleted = new Chilkat.Dns.TaskIdCompleted(handleTaskIdCompleted);
dns.setTaskIdCompletedCb(taskIdCompleted);
```

## Async variants

Each returns a `Task` instead of the result and takes the same arguments as the synchronous method; run the task, wait for `Finished`, then read the result from the task. No new Async methods are added from 11.7.0 on.

```csharp
public Task QueryAsync(string recordType, string domain, JsonObject answer);
```

## Related classes

[`JsonObject`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/csharp/classes/JsonObject.md)