Microsoft Docs

IPHostResolver Class

Namespace: System.Net
Assembly: System.Net.Primitives

Provides methods for performing DNS lookups and translating host names to IP addresses and vice versa. This class is the primary entry point for resolving network endpoint information.

Syntax

public class IPHostResolver : object

Remarks

The IPHostResolver class is used to resolve host names, such as "www.example.com", into IP addresses. It can also resolve IP addresses back into host names, if that information is available in DNS. This is a fundamental part of network communication, allowing applications to connect to services using easily memorable names instead of numerical IP addresses.

Instances of IPHostResolver can be obtained from the System.Net.Dns class.

Methods

GetHostEntry(string hostName)

Asynchronously resolves a host name to an array of IP addresses and an array of aliases.

public Task<IPHostEntry> GetHostEntryAsync(string hostName)

Parameters

Name Type Description
hostName string The host name to resolve.

Returns

A Task<IPHostEntry> that represents the asynchronous operation. The Result property of the task contains an IPHostEntry object that holds the IP addresses and aliases for the host.

GetHostEntry(IPAddress address)

Asynchronously resolves an IP address to a host name and an array of aliases.

public Task<IPHostEntry> GetHostEntryAsync(IPAddress address)

Parameters

Name Type Description
address IPAddress The IP address to resolve.

Returns

A Task<IPHostEntry> that represents the asynchronous operation. The Result property of the task contains an IPHostEntry object that holds the host name and aliases for the IP address.

GetHostAddresses(string hostName)

Asynchronously resolves a host name to an array of IP addresses.

public Task<IPAddress[]> GetHostAddressesAsync(string hostName)

Parameters

Name Type Description
hostName string The host name to resolve.

Returns

A Task<IPAddress[]> that represents the asynchronous operation. The Result property of the task contains an array of IPAddress objects.

Example


using System;
using System.Net;
using System.Threading.Tasks;

public class DnsLookup
{
    public static async Task Main(string[] args)
    {
        string hostname = "www.microsoft.com";
        IPHostResolver resolver = new IPHostResolver(); // In modern .NET, you'd typically use Dns.GetHostResolver() or Dns.GetHostEntryAsync() directly

        try
        {
            Console.WriteLine($"Resolving host: {hostname}");
            IPHostEntry hostEntry = await resolver.GetHostEntryAsync(hostname); // Or await Dns.GetHostEntryAsync(hostname);

            Console.WriteLine($"Host name: {hostEntry.HostName}");

            Console.WriteLine("IP Addresses:");
            foreach (IPAddress ipAddress in hostEntry.AddressList)
            {
                Console.WriteLine($"- {ipAddress}");
            }

            if (hostEntry.Aliases.Length > 0)
            {
                Console.WriteLine("Aliases:");
                foreach (string alias in hostEntry.Aliases)
                {
                    Console.WriteLine($"- {alias}");
                }
            }
        }
        catch (SocketException ex)
        {
            Console.WriteLine($"Error resolving host: {ex.Message}");
        }
    }
}
Note: In modern .NET (Core and later), the static members of the System.Net.Dns class (like Dns.GetHostEntryAsync) are the preferred way to perform DNS lookups. The IPHostResolver class is more of an underlying component.

See Also