Plan and Install Active Directory - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 173

Server 2012 R2 function level as long as all domain controllers are running Windows
Server 2012 R2.
When you are deciding which function level you will use in your organization, you must
choose the function level of your lowest domain controller. For example, if you have a Win-
dows Server 2003 domain controller, your function levels should be Windows Server 2003.
If you choose a higher level, the Windows Server 2003 domain controller will not function.
Be careful—once a forest function level is upgraded, it cannot be downgraded lower than
Windows Server 2008.
Table 3.1 shows the features available in Windows Server 2003, Windows Server 2008,
Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2 domain
function levels.

TAble 3.1 Comparing domain functional levels

Domain functional
feature

Windows
Server 2003

Windows
Server 2008

Windows
Server 2008 R2

Windows
Server 2012

Windows
Server 2012 R2

Authentication
assurance

Disabled Disabled Enabled Enabled Enabled

Fine-grained pass-
word policies

Disabled Enabled Enabled Enabled Enabled

Last interactive
logon information

Disabled Enabled Enabled Enabled Enabled

Advanced Encryp-
tion Services (AES
128 and 256) sup-
port for the Kerbe-
ros protocol

Disabled Enabled Enabled Enabled Enabled

Distributed File
System replication
support for Sysvol

Disabled Enabled Enabled Enabled Enabled

Read-only domain
controller (RODC)

Enabled Enabled Enabled Enabled Enabled

Ability to redirect
the Users and
Computers
containers

Enabled Enabled Enabled Enabled Enabled

Ability to
rename domain
controllers

Enabled Enabled Enabled Enabled Enabled