The AppDynamics for Databases collector connects to SQL Server via JDBC (Java Database Connectivity), which works over a TCP/IP protocol. The collector requires the following:

• SQL Server must have TCP/IP protocol enabled.
• You must enter the port number of the SQL Server listener port (the default is 1433)
• Network connectivity must exist between your AppDynamics for Databases machine and the SQL Server machine (for example make sure there is no blocking firewall).

The following error usually points to an incorrectly entered listener port number, or TCP/IP disabled on the monitored SQL Server:

Unable to establish a connection. com.microsoft.sqlserver.jdbc.SQLServerException: The TCP/IP connection to the host has failed. java.net.ConnectException: Connection refused: connect

Failed Connection to SQL Server

If you have named or multiple SQL Server instances and have dynamically assigned ports for those instances, then 

• When configuring the collector for a specific instance, use only the host name for the "Hostname or IP Address:" field
• For the "Database Listener Port:" field, use the dynamic port number that is in use by the instance you want to connect to.

The collector connection does not currently support using the browser service, so you must specify the dynamic port number associated with the instance you want to monitor.