diff --git a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj
index b2c1017fc1..77c2150b7b 100644
--- a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj
+++ b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj
@@ -659,6 +659,9 @@
     <Compile Include="Microsoft\Data\SqlClient\SqlColumnEncryptionCertificateStoreProvider.Windows.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SqlColumnEncryptionCngProvider.Windows.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SqlColumnEncryptionCspProvider.Windows.cs" />
+    <Compile Include="..\..\src\Microsoft\Data\SqlClient\TdsParserSafeHandles.Windows.cs">
+      <Link>Microsoft\Data\SqlClient\TdsParserSafeHandles.Windows.cs</Link>
+    </Compile>
   </ItemGroup>
   <!-- Unix only -->
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
@@ -744,7 +747,6 @@
     <Compile Include="Microsoft\Data\ProviderBase\DbConnectionPoolIdentity.Windows.cs" />
     <Compile Include="Microsoft\Data\SqlClient\LocalDBAPI.Windows.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SNI\LocalDB.Windows.cs" />
-    <Compile Include="Microsoft\Data\SqlClient\TdsParserSafeHandles.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParserStateObjectNative.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParser.Windows.cs" />
   </ItemGroup>
diff --git a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj
index 93b2fe8ca9..1c4f848df9 100644
--- a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj
+++ b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj
@@ -554,6 +554,9 @@
     <Compile Include="..\..\src\Microsoft\Data\SqlClient\TdsParameterSetter.cs">
       <Link>Microsoft\Data\SqlClient\TdsParameterSetter.cs</Link>
     </Compile>
+    <Compile Include="..\..\src\Microsoft\Data\SqlClient\TdsParserSafeHandles.Windows.cs">
+      <Link>Microsoft\Data\SqlClient\TdsParserSafeHandles.Windows.cs</Link>
+    </Compile>
     <Compile Include="..\..\src\Microsoft\Data\SqlClient\TdsParserStaticMethods.cs">
       <Link>Microsoft\Data\SqlClient\TdsParserStaticMethods.cs</Link>
     </Compile>
@@ -648,7 +651,6 @@
     <Compile Include="Microsoft\Data\SqlClient\SqlUtil.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParser.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParserHelperClasses.cs" />
-    <Compile Include="Microsoft\Data\SqlClient\TdsParserSafeHandles.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParserSessionPool.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParserStateObject.cs" />
     <Compile Include="Microsoft\Data\SqlTypes\SqlFileStream.cs" />
diff --git a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs
index 664c6e56d5..1ecb6c6ce8 100644
--- a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs
+++ b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs
@@ -521,7 +521,7 @@ internal void Connect(ServerInfo serverInfo,
             // Clean up IsSQLDNSCachingSupported flag from previous status
             _connHandler.IsSQLDNSCachingSupported = false;
 
-            UInt32 sniStatus = SNILoadHandle.SingletonInstance.SNIStatus;
+            UInt32 sniStatus = SNILoadHandle.SingletonInstance.Status;
             if (sniStatus != TdsEnums.SNI_SUCCESS)
             {
                 _physicalStateObj.AddError(ProcessSNIError(_physicalStateObj));
diff --git a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.Windows.cs
similarity index 85%
rename from src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.cs
rename to src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.Windows.cs
index 3db0f07fcf..8d2716c63e 100644
--- a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.cs
+++ b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.Windows.cs
@@ -5,8 +5,12 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Threading;
+#if NETFRAMEWORK
+using Microsoft.Data.Common;
+#endif
 
 namespace Microsoft.Data.SqlClient
 {
@@ -23,7 +27,7 @@ internal sealed partial class SNILoadHandle : SafeHandle
 
         private SNILoadHandle() : base(IntPtr.Zero, true)
         {
-            // From security review - SafeHandle guarantees this is only called once.
+            // SQL BU DT 346588 - from security review - SafeHandle guarantees this is only called once.
             // The reason for the safehandle is guaranteed initialization and termination of SNI to
             // ensure SNI terminates and cleans up properly.
             try
@@ -49,7 +53,7 @@ public bool ClientOSEncryptionSupport
                     {
                         try
                         {
-                            UInt32 value = 0;
+                            uint value = 0;
                             // Query OS to find out whether encryption is supported.
                             SNINativeMethodWrapper.SNIQueryInfo(SNINativeMethodWrapper.QTypes.SNI_QUERY_CLIENT_ENCRYPT_POSSIBLE, ref value);
                             _clientOSEncryptionSupport = value != 0;
@@ -101,7 +105,11 @@ private static void ReadDispatcher(IntPtr key, IntPtr packet, uint error)
 
                 if (null != stateObj)
                 {
+#if NETFRAMEWORK
+                    stateObj.ReadAsyncCallback(IntPtr.Zero, packet, error);
+#else
                     stateObj.ReadAsyncCallback(IntPtr.Zero, PacketHandle.FromNativePointer(packet), error);
+#endif // NETFRAMEWORK
                 }
             }
         }
@@ -122,7 +130,11 @@ private static void WriteDispatcher(IntPtr key, IntPtr packet, uint error)
 
                 if (null != stateObj)
                 {
+#if NETFRAMEWORK
+                    stateObj.WriteAsyncCallback(IntPtr.Zero, packet, error);
+#else
                     stateObj.WriteAsyncCallback(IntPtr.Zero, PacketHandle.FromNativePointer(packet), error);
+#endif // NETFRAMEWORK
                 }
             }
         }
@@ -144,12 +156,17 @@ internal SNIHandle(
             bool flushCache,
             bool fSync,
             bool fParallel,
+#if NETFRAMEWORK
+            TransparentNetworkResolutionState transparentNetworkResolutionState,
+            int totalTimeout,
+#endif
             SqlConnectionIPAddressPreference ipPreference,
             SQLDNSInfo cachedDNSInfo,
             bool tlsFirst,
             string hostNameInCertificate)
             : base(IntPtr.Zero, true)
         {
+            RuntimeHelpers.PrepareConstrainedRegions();
             try
             { }
             finally
@@ -158,11 +175,21 @@ internal SNIHandle(
                 instanceName = new byte[256]; // Size as specified by netlibs.
                 if (ignoreSniOpenTimeout)
                 {
+                    // UNDONE: ITEM12001110 (DB Mirroring Reconnect) Old behavior of not truly honoring timeout presevered 
+                    //  for non-failover scenarios to avoid breaking changes as part of a QFE.  Consider fixing timeout
+                    //  handling in next full release and removing ignoreSniOpenTimeout parameter.
                     timeout = Timeout.Infinite; // -1 == native SNIOPEN_TIMEOUT_VALUE / INFINITE
                 }
 
-                _status = SNINativeMethodWrapper.SNIOpenSyncEx(myInfo, serverName, ref base.handle, spnBuffer, instanceName, flushCache,
-                    fSync, timeout, fParallel, ipPreference, cachedDNSInfo, hostNameInCertificate);
+#if NETFRAMEWORK
+                int transparentNetworkResolutionStateNo = (int)transparentNetworkResolutionState;
+                _status = SNINativeMethodWrapper.SNIOpenSyncEx(myInfo, serverName, ref base.handle,
+                            spnBuffer, instanceName, flushCache, fSync, timeout, fParallel, transparentNetworkResolutionStateNo, totalTimeout,
+                            ADP.IsAzureSqlServerEndpoint(serverName), ipPreference, cachedDNSInfo, hostNameInCertificate);
+#else
+                _status = SNINativeMethodWrapper.SNIOpenSyncEx(myInfo, serverName, ref base.handle,
+                            spnBuffer, instanceName, flushCache, fSync, timeout, fParallel, ipPreference, cachedDNSInfo, hostNameInCertificate);
+#endif // NETFRAMEWORK
             }
         }