From b2e9439a5381eab8c52bcd0414e2d18d2e829e8c Mon Sep 17 00:00:00 2001
From: Eric Kohl <eric.kohl@reactos.org>
Date: Mon, 6 Apr 2026 14:13:07 +0200
Subject: [PATCH] [NETCFGX] Call DhcpFallbackRefreshParams when the alternate
 configuration has been changed

---
 dll/win32/netcfgx/tcpipconf_notify.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/dll/win32/netcfgx/tcpipconf_notify.c b/dll/win32/netcfgx/tcpipconf_notify.c
index af91ad83186..1de63d78876 100644
--- a/dll/win32/netcfgx/tcpipconf_notify.c
+++ b/dll/win32/netcfgx/tcpipconf_notify.c
@@ -6,6 +6,8 @@
 #include <dhcpcsdk.h>
 #include <dhcpcapi.h>
 
+typedef DWORD (WINAPI *PDHCPFALLBACKREFRESHPARAMS)(PWSTR pAdapterName);
+
 typedef struct
 {
     DWORD EnableSecurityFilters;
@@ -3789,6 +3791,7 @@ INetCfgComponentControl_fnApplyPnpChanges(
     INetCfgPnpReconfigCallback *pICallback)
 {
     TcpipSettings *pCurrentConfig, *pOldConfig;
+    LPOLESTR pAdapterName;
     ULONG NTEInstance;
     DWORD DhcpApiVersion;
     DWORD dwSize;
@@ -3797,6 +3800,11 @@ INetCfgComponentControl_fnApplyPnpChanges(
 
     TcpipConfNotifyImpl *This = (TcpipConfNotifyImpl*)iface;
 
+    if (FAILED(StringFromCLSID(&This->NetCfgInstanceId, &pAdapterName)))
+    {
+        return E_FAIL;
+    }
+
     pCurrentConfig = This->pCurrentConfig;
     pOldConfig = This->pOldConfig;
 
@@ -3895,6 +3903,20 @@ INetCfgComponentControl_fnApplyPnpChanges(
         CreateIpForwardEntry(&RouterMib);
     }
 
+
+    /* Notify the DHCP client of the changed alternate configuration */
+    if (!RtlEqualMemory(&pCurrentConfig->AltConfig, &pOldConfig->AltConfig, sizeof(AlternateConfiguration)))
+    {
+        HMODULE hDhcpModule = LoadLibraryW(L"dhcpcsvc.dll");
+        if (hDhcpModule)
+        {
+            PDHCPFALLBACKREFRESHPARAMS pFunc = (PDHCPFALLBACKREFRESHPARAMS)GetProcAddress(hDhcpModule, "DhcpFallbackRefreshParams");
+            (pFunc)(pAdapterName);
+
+            FreeLibrary(hDhcpModule);
+        }
+    }
+
     return S_OK;
 }