SQL Server Pre-Login Handshake

Question

I'm connecting to MSSQL database through my ASP .NET application, but sometimes I got this error while opening connection.

Connection Timeout Expired. The timeout period elapsed while attempting to consume the pre-login handshake acknowledgement. This could be because the pre-login handshake failed or the server was unable to respond back in time. The duration spent while attempting to connect to this server was - [Pre-Login] initialization=3; handshake=14996;

To solve it temporarily I've to restart IIS. I'm using this code snippet to connect to MSSQL:

        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            /* my commands here */

            connection.Close();
            connection.Dispose();
            SqlConnection.ClearPool(connection);
        }

I allowed the port 1433 in the inbound and outbound rules, but no changes. As I follow the instructions there:

• SQL Server Pre-Login Handshake Acknowledgement Error
• Connection to SQL Server Works Sometimes

but nothing changed.

Answer 1

According MSDN Doc .

ClearPool clears the connection pool that is associated with the connection.If additional connections associated with connection are in use at the time of the call, they are marked appropriately and are discarded (instead of being returned to the pool) when Close is called on them.

you should use ClearPool method before connection.close

refer : https://msdn.microsoft.com/zh-tw/library/system.data.sqlclient.sqlconnection.clearpool(v=vs.110).aspx

And If you use Using syntax to manage Object you should't use connection.close method

because it will call when they run to end . just open your connection and execute your command

 using (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();
        SqlConnection.ClearPool(connection);
        /* my commands here */
        SqlCommand cmd = new SqlCommand("your command",conn);
        cmd.ExecuteReader()


    }

refer example : https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396

last ensure SQL Server Network Config is right

Answer 2

What did the trick for me is increasing the timeout on the connection string, since when connecting by vpn it took to long to establish the connection. You can do this by adding ;connection timeout = value

I got the same error when connecting an application tried to connect to sql server while I was on a vpn.

By default the timeout is set to 15 seconds.

Hope it helps!