The file with .udl extension is called Microsoft Universal Data Link file; specifying connection attributes; used by Windows apps to establish a connection with the database. The UDL file contains the connection string for an OLE DB data source; with username and password and essential connection string properties. To avoid directly specifying the properties by hand in a connection string, a Data Link Properties dialog box can be used to save connection information in a .udl file as an alternative.
UDL File Format
Basically, a UDL (Universal Data Link) file is a simple text file that consists of a database connection string with particular attributes or properties. Once the UDL file is created, it can be tested by using SQL Server Management Studio to verify the connectivity.
Connection string properties
Following properties can be set in a UDL to ensure the proper connectivity:
Server Name: location of the server where the database you want to access is located.
Windows Authentication: Authentication to SQL Server using the currently logged-in user’s Windows account credentials.
SQL Server Authentication: Authentication using login ID and password.
Active Directory - Integrated: Integrated authentication with an Azure Active Directory identity; can also be used for Windows authentication to SQL Server.
Active Directory - Password: User ID and password authentication with an Azure Active Directory identity.
Active Directory - Universal with MFA support: Interactive authentication with an Azure Active Directory identity.
Active Directory - Service Principal: Authentication with an Azure Active Directory service principal.
Server SPN: If you use a trusted connection, you can specify a service principal name (SPN) for the server.
User name: Type the User ID to use for authentication when you sign in to the data source.
Password: Type the password to use for authentication when you sign in to the data source.
Blank password: When checked, enables the specified provider to use a blank password in the connection string.
Allow saving password: Allows the password to be saved with the connection string.
Use strong encryption for data: data that is passed through the connection will be encrypted.
Trust server certificate: The server’s certificate will be validated.
Database: Database name that you want to access.
Attach a database file as a database name: Specifies the name of the primary file for an attachable database.