Fix: Detect local IP address (& 169.254) as fallback when routing is not available

Source/NETworkManager.Profiles/ProfileManager.cs

@@ -479,7 +479,7 @@ public static void Save()
 
             return;
         }
-            
+
 
         Directory.CreateDirectory(GetProfilesFolderLocation());
 

Source/NETworkManager/ViewModels/IPScannerViewModel.cs

@@ -347,7 +347,7 @@ private void ScanAction()
 
     private void DetectSubnetAction()
     {
-        DetectIPRange().ConfigureAwait(false);
+        DetectSubnet().ConfigureAwait(false);
     }
 
     /// <summary>
@@ -530,34 +530,47 @@ private void Stop()
     }
 
     /// <summary>
-    /// Detects the local IP subnet.
+    /// Attempts to detect the local subnet and updates the host information accordingly.
     /// </summary>
-    private async Task DetectIPRange()
+    /// <remarks>If the subnet or local IP address cannot be detected, an error message is displayed to the
+    /// user. The method updates the Host property with the detected subnet in CIDR notation when successful.</remarks>
+    /// <returns>A task that represents the asynchronous subnet detection operation.</returns>
+    private async Task DetectSubnet()
     {
         IsSubnetDetectionRunning = true;
 
+        // Try to detect local IP address based on routing to public IP
         var localIP = await NetworkInterface.DetectLocalIPAddressBasedOnRoutingAsync(IPAddress.Parse(GlobalStaticConfiguration.Dashboard_PublicIPv4Address));
 
-        // Could not detect local ip address
+        // Fallback: Try to detect local IP address from network interfaces -> Prefer non link-local addresses
+        localIP ??= await NetworkInterface.DetectLocalIPAddressFromNetworkInterfaceAsync(System.Net.Sockets.AddressFamily.InterNetwork);
+
+        // If local IP address detected, try to find subnetmask from network interfaces
         if (localIP != null)
         {
-            var subnetmaskDetected = false;
+            var subnetDetected = false;
+
+            // Get network interfaces, where local IP address is assigned
+            var networkInterface = (await NetworkInterface.GetNetworkInterfacesAsync())
+                .FirstOrDefault(x => x.IPv4Address.Any(y => y.Item1.Equals(localIP)));
 
-            // Get subnetmask, based on ip address
-            foreach (var networkInterface in (await NetworkInterface.GetNetworkInterfacesAsync()).Where(
-                         networkInterface => networkInterface.IPv4Address.Any(x => x.Item1.Equals(localIP))))
+            // If found, get subnetmask
+            if (networkInterface != null)
             {
-                subnetmaskDetected = true;
 
-                Host = $"{localIP}/{Subnetmask.ConvertSubnetmaskToCidr(networkInterface.IPv4Address.First().Item2)}";
+                // Find the correct IP address and the associated subnetmask
+                var ipAddressWithSubnet = networkInterface.IPv4Address.First(x => x.Item1.Equals(localIP));
+
+                Host = $"{ipAddressWithSubnet.Item1}/{Subnetmask.ConvertSubnetmaskToCidr(ipAddressWithSubnet.Item2)}";
+
+                subnetDetected = true;
 
                 // Fix: If the user clears the TextBox and then clicks again on the button, the TextBox remains empty...
                 OnPropertyChanged(nameof(Host));
-
-                break;
             }
 
-            if (!subnetmaskDetected)
+            // Show error message if subnet could not be detected
+            if (!subnetDetected)
             {
                 var window = Application.Current.Windows.OfType<Window>().FirstOrDefault(x => x.IsActive);
 
@@ -716,8 +729,9 @@ public void OnClose()
     private void HostScanned(object sender, IPScannerHostScannedArgs e)
     {
         Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
-            new Action(delegate { 
-                Results.Add(e.Args); 
+            new Action(delegate
+            {
+                Results.Add(e.Args);
             }));
     }
 

Source/NETworkManager/ViewModels/NetworkConnectionWidgetViewModel.cs

@@ -901,7 +901,7 @@ await NetworkInterface.DetectLocalIPAddressBasedOnRoutingAsync(
                 Log.Debug("CheckConnectionRouterAsync - Computer IPv4 address detected: " + detectedLocalIPv4Address);
 
                 var detectedRouterIPv4 =
-                    await NetworkInterface.DetectGatewayBasedOnLocalIPAddressAsync(
+                    await NetworkInterface.DetectGatewayFromLocalIPAddressAsync(
                         detectedLocalIPv4Address);
 
                 if (detectedRouterIPv4 != null)
@@ -944,7 +944,7 @@ await NetworkInterface.DetectLocalIPAddressBasedOnRoutingAsync(
                 Log.Debug("CheckConnectionRouterAsync - Computer IPv6 address detected: " + detectedComputerIPv6);
 
                 var detectedRouterIPv6 =
-                    await NetworkInterface.DetectGatewayBasedOnLocalIPAddressAsync(detectedComputerIPv6);
+                    await NetworkInterface.DetectGatewayFromLocalIPAddressAsync(detectedComputerIPv6);
 
                 if (detectedRouterIPv6 != null)
                 {

Website/docs/application/ip-scanner.md

@@ -27,7 +27,16 @@ Example: `10.0.0.0/24; 10.0.[10-20]1`
 
 :::
 
-The button to the left of the `Scan` button determines the IP address and subnet mask of the network interface currently in use in order to scan the local subnet for active devices.
+The button to the left of the `Scan` button determines the IP address and subnet mask of the network interface
+currently in use in order to scan the local subnet for active devices.
+
+:::note
+
+The local IP address (and subnet mask) is determined by trying to route to a public IP address. If this fails (e.g. 
+no network connection), NETworkManager iterates over active network adapters and selects the first valid IPv4 address,
+with link-local addresses (`169.254.x.x`) given lower priority.
+
+:::
 
 If you right-click on a selected result, you can forward the device information to other applications (e.g. Port Scanner, Remote Desktop, etc), create a new profile with this information or execute a [custom command](#custom-commands).
 

Website/docs/changelog/next-release.md

@@ -56,6 +56,10 @@ Release date: **xx.xx.2025**
 - Settings format migrated from `XML` to `JSON`. The settings file will be automatically converted on first start after the update. [#3282](https://github.com/BornToBeRoot/NETworkManager/pull/3282)
 - Create a daily backup of the settings file before saving changes. Up to `10` backup files are kept in the `Backups` subfolder of the settings directory. [#3283](https://github.com/BornToBeRoot/NETworkManager/pull/3283)
 
+**IP Scanner**
+
+- Improved local subnet detection: If local IP cannot be determined via routing, now iterates over active network adapters and selects the first valid IPv4 address (with link-local addresses (`169.254.x.x`) given lower priority). [#3288](https://github.com/BornToBeRoot/NETworkManager/pull/3288)
+
 **DNS Lookup**
 
 - Allow hostname as server address in addition to IP address in the add/edit server dialog. [#3261](https://github.com/BornToBeRoot/NETworkManager/pull/3261)