Dns.BeginResolve Method (String, AsyncCallback, Object)


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Note: This API is now obsolete.

Begins an asynchronous request to resolve a DNS host name or IP address to an IPAddress instance.

Namespace:   System.Net
Assembly:  System (in System.dll)

[ObsoleteAttribute("BeginResolve is obsoleted for this type, please use BeginGetHostEntry instead. http://go.microsoft.com/fwlink/?linkid=14202")]
[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public static IAsyncResult BeginResolve(
	string hostName,
	AsyncCallback requestCallback,
	object stateObject


Type: System.String

The DNS name of the host.

Type: System.AsyncCallback

An AsyncCallback delegate that references the method to invoke when the operation is complete.

Type: System.Object

A user-defined object that contains information about the operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

Type: System.IAsyncResult

An IAsyncResult instance that references the asynchronous request.

Exception Condition

hostName is null.


The caller does not have permission to access DNS information.

The asynchronous BeginResolve operation must be completed by calling the EndResolve method. Typically, the method is invoked by the requestCallback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use the Resolve method.

For more information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.


This member emits trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.

The following example uses BeginResolve to resolve a DNS host name to an IPAddress.

class DnsBeginGetHostByName
   public static System.Threading.ManualResetEvent allDone = null;

   class RequestState
      public IPHostEntry host;
      public RequestState()
         host = null;

   public static void Main()
     allDone = new ManualResetEvent(false);
     // Create an instance of the RequestState class.
     RequestState myRequestState = new RequestState();

     // Begin an asynchronous request for information like host name, IP addresses, or 
     // aliases for specified the specified URI.
     IAsyncResult asyncResult = Dns.BeginResolve("www.contoso.com", new AsyncCallback(RespCallback), myRequestState );

     // Wait until asynchronous call completes.
     Console.WriteLine("Host name : " + myRequestState.host.HostName);
     Console.WriteLine("\nIP address list : ");
     for(int index=0; index < myRequestState.host.AddressList.Length; index++)
     Console.WriteLine("\nAliases : ");
     for(int index=0; index < myRequestState.host.Aliases.Length; index++)

   private static void RespCallback(IAsyncResult ar)
       // Convert the IAsyncResult object to a RequestState object.
       RequestState tempRequestState = (RequestState)ar.AsyncState;
       // End the asynchronous request.
       tempRequestState.host = Dns.EndResolve(ar);
	   catch(ArgumentNullException e) 
       Console.WriteLine("ArgumentNullException caught!!!");
       Console.WriteLine("Source : " + e.Source);
       Console.WriteLine("Message : " + e.Message);
     catch(Exception e)
       Console.WriteLine("Exception caught!!!");
       Console.WriteLine("Source : " + e.Source);
       Console.WriteLine("Message : " + e.Message);


for accessing DNS information. Associated enumeration: PermissionState.Unrestricted

.NET Framework
Available since 1.1
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