How to check if DNS server is set to 'obtain a

问题:

When I get my servers DNS settings using the DNSServerSearchOrder property of my network card's settings, it returns the DNS server that it automatically resolves to, rather than a value that would indicate it is dynamic (such as null).

for example, to set my DNS servers to 'Obtain Automatically' I do:

ManagementBaseObject newDNS = myNICManagementObject.GetMethodParameters("SetDNSServerSearchOrder");
newDNS["DNSServerSearchOrder"] = null;
ManagementBaseObject setDNS = myNICManagementObject.InvokeMethod("SetDNSServerSearchOrder", newDNS, null);

Now, after I have set it to 'Obtain Automatically' with the other command I want to confirm it was set:

if( myNICManagementObject["DNSServerSearchOrder"] == null )
{
    MessageBox.Show("DNS Servers Set to Dynamic!");
}

However, the above code does not return null (nor pop-up a messagebox) as expected. Instead it returns the DNS server that it dynamically figures out from my ISP.

Is there a way to determine programmatically that my DNS servers are set to 'Obtain Automatically'?

回答1:

The only way I found is to read from the registry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\\{Network_Adaptor_GUID}\NameServer

If NameServer is empty - then DNS is dynamic, otherwise - static.

回答2:

Vad's answer saved me a ton of time hunting for a solution. Here's some C# if anyone wants to see a very basic implementation.

using Microsoft.Win32;
//...
private void DNSAutoOrStatic(string NetworkAdapterGUID)
        {
            string path = "HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Interfaces\\" + NetworkAdapterGUID;
            string ns = (string)Registry.GetValue(path, "NameServer", null);
            if (String.IsNullOrEmpty(ns))
            {
                Console.WriteLine("Dynamic DNS");
            }
            else
            {
                Console.WriteLine("Static DNS: " + ns);
            }
        }

You can get the network adapter GUID following these examples.

It's the value of the Id property in System.Net.NetworkInformation.NetworkInterface