This topic describes how to fix the issue if the Data Transmission Service (DTS) instance cannot connect to the source or destination database.
Issue
When you configure a data migration task or data synchronization task, both the source and destination databases pass the connectivity test. However, during the precheck, the message "The DTS instance cannot connect to the source or destination database" appears.
Cause
No whitelists are configured for the source and destination databases, or the whitelist
settings are incomplete. As a result, the DTS instance cannot connect to the source
or destination database.
Note The connection failure is likely to occur when you configure a cross-region migration
or synchronization task, or when the source database is a user-created database.
Solution
Configure whitelists for the source and destination databases. For more information, see Whitelist DTS IP ranges for your user-created database.