Feature: DNS server

Author: BornToBeRoot

Source/NETworkManager.Models/Network/DNSLookup.cs

@@ -1,10 +1,10 @@
 using DnsClient;
 using DnsClient.Protocol;
+using NETworkManager.Utilities;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
-using System.Net.NetworkInformation;
 using System.Threading.Tasks;
 
 namespace NETworkManager.Models.Network;
@@ -24,7 +24,7 @@ public DNSLookup(DNSLookupSettings settings, IEnumerable<ServerConnectionInfo> d
         {
             _suffix = _settings.UseCustomDNSSuffix
                 ? _settings.CustomDNSSuffix
-                : IPGlobalProperties.GetIPGlobalProperties().DomainName;
+                : DNSClientHelper.DetectDNSSuffix();
 
             _addSuffix = !string.IsNullOrEmpty(_suffix);
         }

Source/NETworkManager.Utilities/DNSClient.cs

@@ -43,11 +43,9 @@ public class DNSClient : SingletonBase<DNSClient>
     /// <param name="settings"></param>
     public void Configure(DNSClientSettings settings)
     {
-        _settings = settings;
-
-        _addSuffix = _settings.AddDNSSuffix && !string.IsNullOrEmpty(_settings.DNSSuffix);
-
         Log.Debug("Configure - Configuring DNS client...");
+        
+        _settings = settings;
 
         if (_settings.UseCustomDNSServers)
         {
@@ -63,14 +61,19 @@ public void Configure(DNSClientSettings settings)
             }
 
             Log.Debug("Configure - Creating LookupClient with custom DNS servers...");
-            _client = new LookupClient(new LookupClientOptions(servers.ToArray()));
+            _client = new LookupClient(new LookupClientOptions([.. servers]));
         }
         else
         {
             Log.Debug("Configure - Creating LookupClient with Windows default DNS servers...");
             _client = new LookupClient();
         }
 
+        _addSuffix = _settings.AddDNSSuffix && !string.IsNullOrEmpty(_settings.DNSSuffix);
+        Log.Debug(_addSuffix
+            ? $"Configure - DNS suffix will be added to hostnames without a dot: {_settings.DNSSuffix}"
+            : "Configure - DNS suffix will NOT be added to hostnames without a dot.");
+
         Log.Debug("Configure - DNS client configured.");
         _isConfigured = true;
     }

Source/NETworkManager.Utilities/DNSClientHelper.cs

@@ -1,9 +1,48 @@
-using System.Threading.Tasks;
+using System.Linq;
+using System.Net.NetworkInformation;
+using System.Threading.Tasks;
 
 namespace NETworkManager.Utilities;
 
 public static class DNSClientHelper
 {
+    /// <summary>
+    ///     Detect the DNS suffix to use for suffix-appending. Prefers the Windows "Primary DNS Suffix"
+    ///     (<see cref="IPGlobalProperties.DomainName" />), falling back to the connection-specific suffix
+    ///     of an active network adapter if no primary suffix is configured (e.g. machine is not domain-joined
+    ///     or the primary suffix was cleared manually), which mirrors what shows up under "DNS Suffix Search
+    ///     List" in <c>ipconfig /all</c> in that case.
+    /// </summary>
+    public static string DetectDNSSuffix()
+    {
+        var suffix = IPGlobalProperties.GetIPGlobalProperties().DomainName;
+
+        if (!string.IsNullOrWhiteSpace(suffix))
+            return suffix;
+
+        // Rank candidates so the adapter most likely to be "the" active connection is tried first:
+        // routed (has a gateway) > wired > wireless > other > faster link speed.
+        var prioritizedAdapters = NetworkInterface.GetAllNetworkInterfaces()
+            .Where(nic => nic.OperationalStatus == OperationalStatus.Up &&
+                          nic.NetworkInterfaceType != NetworkInterfaceType.Loopback &&
+                          nic.NetworkInterfaceType != NetworkInterfaceType.Tunnel)
+            .OrderByDescending(nic => nic.GetIPProperties().GatewayAddresses.Count > 0)
+            .ThenByDescending(nic => GetInterfaceTypePriority(nic.NetworkInterfaceType))
+            .ThenByDescending(nic => nic.Speed);
+
+        return prioritizedAdapters
+            .Select(nic => nic.GetIPProperties().DnsSuffix)
+            .FirstOrDefault(s => !string.IsNullOrWhiteSpace(s))
+            ?? string.Empty;
+    }
+
+    private static int GetInterfaceTypePriority(NetworkInterfaceType type) => type switch
+    {
+        NetworkInterfaceType.Ethernet => 2,
+        NetworkInterfaceType.Wireless80211 => 1,
+        _ => 0
+    };
+
     public static async Task<DNSClientResultIPAddress> ResolveAorAaaaAsync(string query, bool preferIPv4)
     {
         DNSClientResultIPAddress firstResult = null;

Source/NETworkManager/MainWindow.xaml.cs

@@ -1922,7 +1922,7 @@ .. SettingsManager.Current.Network_CustomDNSServers
             dnsSettings.AddDNSSuffix = true;
             dnsSettings.DNSSuffix = SettingsManager.Current.Network_UseCustomDNSSuffix
                 ? SettingsManager.Current.Network_CustomDNSSuffix?.TrimStart('.')
-                : IPGlobalProperties.GetIPGlobalProperties().DomainName;
+                : DNSClientHelper.DetectDNSSuffix();
         }
 
         DNSClient.GetInstance().Configure(dnsSettings);

Website/docs/application/dns-lookup.md

@@ -119,7 +119,7 @@ You can also use the Hotkeys `F2` (`edit`) or `Del` (`delete`) on a selected DNS
 
 ### Add DNS suffix (primary) to hostname
 
-Add the primary DNS suffix to the hostname.
+Add the primary DNS suffix to the hostname. If no primary DNS suffix is configured (e.g. the computer is not domain-joined), the connection-specific DNS suffix of the active network adapter is used instead.
 
 **Type:** `Boolean`