AppContext switches in Sqlclient
The AppContext class allows SqlClient to provide new functionality while continuing to support callers who depend on the previous behavior. Users can opt out of a change in behavior by setting specific AppContext switches.
Force use of operating system encryption protocols
Applies to: 
.NET Framework
.NET
.NET Standard
Starting with Microsoft.Data.SqlClient 4.0, TLS 1.3 isn't supported by the driver and was removed from the supported protocols list by default. Users can switch back to forcing use of the operating system's client protocols, by setting the AppContext switch "Switch.Microsoft.Data.SqlClient.UseSystemDefaultSecureProtocols" to true:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.UseSystemDefaultSecureProtocols", true);
Starting with version 5.0, TLS 1.3 is supported in TDS 8 connections without having to use the above switch. TDS 8 is enabled when Encrypt is set to Strict.
Enabling decimal truncation behavior
Applies to:
.NET Framework
.NET
.NET Standard
Starting with Microsoft.Data.SqlClient 2.0, decimal data is rounded by default, as is done by SQL Server. To enable the previous behavior of truncation, you can set the AppContext switch "Switch.Microsoft.Data.SqlClient.TruncateScaledDecimal" to true at application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.TruncateScaledDecimal", true);
Enabling managed networking on Windows
Applies to: 
.NET Framework
.NET Core
.NET Standard
(Available starting with version 2.0)
On Windows, SqlClient uses a native implementation of the SNI network interface by default. To enable the use of a managed SNI implementation, you can set the AppContext switch "Switch.Microsoft.Data.SqlClient.UseManagedNetworkingOnWindows" to true at application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.UseManagedNetworkingOnWindows", true);
This switch toggles the driver's behavior to use a managed networking implementation in .NET Core 2.1+ and .NET Standard 2.0+ projects on Windows, eliminating all dependencies on native libraries for the Microsoft.Data.SqlClient library. It is for testing and debugging purposes only.
Note
There are some known differences when compared to the native implementation. For example, the managed implementation does not support non-domain Windows Authentication.
Disabling Transparent Network IP Resolution
Applies to:
.NET Framework
.NET Core
.NET Standard
Transparent Network IP Resolution (TNIR) is a revision of the existing MultiSubnetFailover feature. TNIR affects the connection sequence of the driver in the case where the first resolved IP of the hostname doesn't respond and there are multiple IPs associated with the hostname. TNIR interacts with MultiSubnetFailover to provide the following three connection sequences:
- 0: One IP is attempted, followed by all IPs in parallel
- 1: All IPs are attempted in parallel
- 2: All IPs are attempted one after another
| TransparentNetworkIPResolution | MultiSubnetFailover | Behavior |
|---|---|---|
| True | True | 1 |
| True | False | 0 |
| False | True | 1 |
| False | False | 2 |
TransparentNetworkIPResolution is enabled by default. MultiSubnetFailover is disabled by default. To disable TNIR, you can set the AppContext switch "Switch.Microsoft.Data.SqlClient.DisableTNIRByDefaultInConnectionString" to true at application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.DisableTNIRByDefaultInConnectionString", true);
For more information about setting these properties, see the documentation for SqlConnection.ConnectionString Property.
Enable a minimum timeout during login
Applies to:
.NET Framework
.NET
.NET Standard
To prevent a login attempt from waiting indefinitely, you can set the AppContext switch Switch.Microsoft.Data.SqlClient.UseOneSecFloorInTimeoutCalculationDuringLogin to true at application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.UseOneSecFloorInTimeoutCalculationDuringLogin", false);
Disable blocking behavior of ReadAsync
Applies to:
.NET Framework
.NET
.NET Standard
Starting in version 3.0, ReadAsync runs asynchronously. Previous versions run ReadAsync synchronously and block the calling thread on .NET Framework. To control this blocking behavior, you can set the AppContext switch Switch.Microsoft.Data.SqlClient.MakeReadAsyncBlocking to true or false at application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.MakeReadAsyncBlocking", false);
Enable configurable retry logic
Applies to:
.NET Framework
.NET
.NET Standard
(Available starting with version 3.0)
By default, configurable retry logic is disabled. To enable this feature, set the AppContext switch Switch.Microsoft.Data.SqlClient.EnableRetryLogic to true at application startup. This switch is required, even if a retry provider is assigned to a connection or command.
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.EnableRetryLogic", true);
- For information on how to enable the switch by using a configuration file see Enable safety switch.
Note
Starting from Microsoft.Data.SqlClient v4.0, the App Context switch "Switch.Microsoft.Data.SqlClient.EnableRetryLogic" will no longer be required to use the configurable retry logic feature. The feature is now supported in production. The default behavior of the feature will continue to be a non-retry policy, which will need to be overridden by client applications to enable retries.
Enabling rowversion null behavior
Applies to:
.NET Framework
.NET
.NET Standard
Starting in version 3.0, when a rowversion has a value of null, SqlDataReader returns a DBNull value instead of an empty byte[]. To enable the legacy behavior of returning an empty byte[], enable the AppContext switch Switch.Microsoft.Data.SqlClient.LegacyRowVersionNullBehavior on application startup.
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.LegacyRowVersionNullBehavior", true);
Suppress insecure TLS warning
Applies to:
.NET Framework
.NET
.NET Standard
(Available starting with version 4.0.1)
When using Encrypt=false in the connection string, a security warning is output to the console if the TLS version is 1.2 or lower. This warning can be suppressed by enabling the following AppContext switch on application startup:
AppContext.SetSwitch("Switch.Microsoft.Data.SqlClient.SuppressInsecureTLSWarning", true);