Microsoft® SQL Server 2012 Unleashed

Mixing Licensing Models

You can mix both core-based and server/CAL licensing models in your organization. If the Internet servers for your organization are segregated from the servers used to support internal applications, you can choose to use core-based licensing for the Internet servers and server/CAL licensing for internal SQL Server instances and user devices.

Keep in mind that you do not need to purchase CALs to allow internal users to access a server already licensed via a server core license: The core licenses allow access to that server for all users.