Appendix H : Securing the *SQL vs. *SQLSRV Server
When securing these servers, note the *SQLSRV functions are only available if the *SQL server is available. (The *SQL server is like the front door to a house, and the *SQLSRV functions are like the various drawers and closets within that house.) You can block all *SQLSRV functions by blocking the *SQL server. When the *SQL server is available, rules can be used to control access to all the *SQL server functions individually.