Rules on licensing SQL Server machines

[vamsimadineni]

Does someone know for certain what the rules on licensing SQL Server machines is with respect to mirrored databases? We are looking a DR scenario where we would be mirroring the databases using Enterprise Edition from one datacenter to another.

My question is: Do we need to purchase licenses for both the Principle node and the mirrored node, or do we need to purchase licenses for only the principle node and we shift that license to the mirrored node when it is in use and the principle node is down.

If someone can please look into this and let me know what the rules are I would appreciate it.

[EINSTEIN_007]

In general, there are three options for licensing SQL Server in a production environment:

Processor License. Under this model, a license is required for each physical or virtual processor that is accessed by an operating system environment running SQL Server software. This license does not require any device or user client access licenses (CALs).

Server plus Device CALs. Under this model, a server license is required for each operating system environment running an instance of SQL Server software, as well as a CAL for each client device that accesses a server running SQL Server.

Server plus User CALs. Under this model, a server license is required for each operating system environment running an instance of SQL Server software, as well as a CAL for each user that accesses a server running SQL Server software.

More information here.