How do I get the DNS Suffix Search List programmatically in C#

Question

How would I get the DNS Suffix Search List on a Windows 10 machine in C#?

For example, if I type ipconfig in cmd I see something like:

Windows IP Configuration

   Host Name . . . . . . . . . . . . : BOB
   Primary Dns Suffix  . . . . . . . : fred.george.com
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : fred.com
                                       george.com

I would like to get an array back of 'fred.com' and 'george.com'. I've tried a few different things[1] but they use the adapters properties (which are blank).

[1] https://docs.microsoft.com/en-us/dotnet/api/system.net.networkinformation.ipinterfaceproperties.dnssuffix?view=netframework-4.8

user_1574221 · Answer

The domain suffixes are stored in registry:

System\CurrentControlSet\Services\Tcpip\Parameters
SearchList (REG_SZ)

The settings are global for for the machine (all adapters and all ip addresses (IPv4 and IPv6))

Use this code to get the string:

string searchList = "";
try
{
    using (var reg = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(tcpSettingsSubKey))
    {
        searchList = (reg.GetValue("SearchList") as string);
    }
}
catch(Exception ex)
{
    // something went wrong
}

I wrote this class to get some more of these settings. In this class the suffixes are stored in DNSSearchListString and DNSSearchList.

using System;
using System.Linq;

/// 
/// Retrieving some IP settings from the registry.
/// The default dns suffix is not stored there but cat be read from:
/// 
/// 
public static class LocalMachineIpSettings
{
    private readonly static object dataReadLock = new object();
    private static bool dataReadFinished = false;

    private static string domain;
    private static string hostname;
    private static int? iPEnableRouter;

    /// 
    /// Search list (the suffixes) as stored in registry
    /// 
    private static string searchListString;

    /// 
    /// Search list (the suffixes) as string array
    /// 
    private static string[] searchList;

    /// 
    /// also available at: 
    /// 
    public static string Domain { get { ReadValues(); return domain; } }
    /// 
    /// also available at: 
    /// 
    public static string Hostname { get { ReadValues(); return hostname; } }
    public static int? IPEnableRouter { get { ReadValues(); return iPEnableRouter; } }
    public static string[] DNSSearchList { get { ReadValues(); return searchList; } }
    public static string DNSSearchListString { get { ReadValues(); return searchListString; } }

    private static void ReadValues()
    {
        lock (dataReadLock)
        {
            if (dataReadFinished == true)
            {
                return;
                //<----------
            }

            ForceRefresh();
        }
    }

    /// 
    /// Reread the values
    /// 
    public static void ForceRefresh()
    {
        const string tcpSettingsSubKey = @"System\CurrentControlSet\Services\Tcpip\Parameters";

        lock (dataReadLock)
        {
            try
            {
                Microsoft.Win32.RegistryKey reg = null;
                using (reg = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(tcpSettingsSubKey))
                {
                    domain = (reg.GetValue("Domain") as string);
                    hostname = (reg.GetValue("Hostname") as string);
                    iPEnableRouter = (reg.GetValue("IPEnableRouter") as int?);
                    searchListString = (reg.GetValue("SearchList") as string);
                    searchList = searchListString?.Split(new[] { ' ', ',', ';' }, StringSplitOptions.RemoveEmptyEntries).Select(o => o.Trim(' ', '.')).ToArray();
                }

                dataReadFinished = true;
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException($"Cannot access HKLM\{ tcpSettingsSubKey } or values beneath see inner exception for details", ex);
                //<----------
            }
        }
    }
}

How do I get the DNS Suffix Search List programmatically in C#

1 Answers