BeginGetHostAddresses Method

Dns.BeginGetHostAddresses Method

Asynchronously returns the Internet Protocol (IP) addresses for the specified host.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public static IAsyncResult BeginGetHostAddresses(
	string hostNameOrAddress,
	AsyncCallback requestCallback,
	Object state


Type: System.String

The host name or IP address to resolve.

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.


hostNameOrAddress is null.


The length of hostNameOrAddress is greater than 126 characters.


An error is encountered when resolving hostNameOrAddress.


hostNameOrAddress is an invalid IP address.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The BeginGetHostAddresses method asynchronously queries a DNS server for the IP addresses that are associated with a host name. If hostNameOrAddress is an IP address, this address is returned without querying the DNS server.


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

When an empty string is passed as the host name, this method returns the IPv4 addresses of the local host for all operating systems except Windows Server 2003; for Windows Server 2003, both IPv4 and IPv6 addresses for the local host are returned.

The asynchronous BeginGetHostAddresses operation must be completed by calling the EndGetHostAddresses 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 GetHostAddresses method.

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

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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