Jose Barreto comments on his TechNet blog:
Note: This blog post is a Windows Server 2012 R2 update on a previous version focused on Windows Server 2012.
With the release of Windows 8.1 and Windows Server 2012 R2, I am frequently asked about how older versions of Windows will behave when connecting to or from these new versions. Upgrading to a new version of SMB is something that happened a few times over the years and we established a process in the protocol itself by which clients and servers negotiate the highest version that both support.
Read up for a good primer on the various versions of the SMB protocol. And whatever you do, don’t call it CIFS!