<s>
A	O
domain	B-General_Concept
controller	I-General_Concept
(	O
DC	O
)	O
is	O
a	O
server	B-Application
that	O
responds	O
to	O
security	O
authentication	O
requests	O
within	O
a	O
computer	B-Architecture
network	I-Architecture
domain	O
.	O
</s>
<s>
It	O
is	O
a	O
network	B-Application
server	I-Application
that	O
is	O
responsible	O
for	O
allowing	O
host	B-Device
access	O
to	O
domain	O
resources	O
.	O
</s>
<s>
It	O
is	O
most	O
commonly	O
implemented	O
in	O
Microsoft	B-Application
Windows	I-Application
environments	O
(	O
see	O
Domain	B-General_Concept
controller	I-General_Concept
(	O
Windows	O
)	O
)	O
,	O
where	O
it	O
is	O
the	O
centerpiece	O
of	O
the	O
Windows	O
Active	B-Protocol
Directory	I-Protocol
service	I-Protocol
.	O
</s>
<s>
However	O
,	O
non-Windows	O
domain	B-General_Concept
controllers	I-General_Concept
can	O
be	O
established	O
via	O
identity	O
management	O
software	O
such	O
as	O
Samba	B-Language
and	O
Red	B-Language
Hat	I-Language
FreeIPA	I-Language
.	O
</s>
<s>
The	O
software	O
and	O
operating	O
system	O
used	O
to	O
run	O
a	O
domain	B-General_Concept
controller	I-General_Concept
usually	O
consists	O
of	O
several	O
key	O
components	O
shared	O
across	O
platforms	B-Device
.	O
</s>
<s>
This	O
includes	O
the	O
operating	O
system	O
(	O
usually	O
Windows	B-Device
Server	I-Device
or	O
Linux	B-Application
)	O
,	O
an	O
LDAP	B-Protocol
service	O
(	O
Red	O
Hat	O
Directory	O
Server	B-Application
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
a	O
network	B-Architecture
time	O
service	O
(	O
ntpd	B-Protocol
,	O
chrony	B-Application
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
and	O
a	O
computer	B-Architecture
network	I-Architecture
authentication	O
protocol	O
(	O
usually	O
Kerberos	B-Protocol
)	O
.	O
</s>
<s>
Other	O
components	O
,	O
such	O
as	O
a	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
(	O
Active	B-Protocol
Directory	I-Protocol
Certificate	O
Services	O
,	O
DogTag	O
,	O
OpenSSL	B-Language
)	O
service	O
and	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
Windows	O
DNS	B-Protocol
or	O
BIND	B-Protocol
)	O
may	O
also	O
be	O
included	O
on	O
the	O
same	O
server	B-Application
or	O
on	O
another	O
domain-joined	O
server	B-Application
.	O
</s>
<s>
Domain	B-General_Concept
controllers	I-General_Concept
are	O
typically	O
deployed	O
as	O
a	O
cluster	B-Architecture
to	O
ensure	O
high-availability	O
and	O
maximize	O
reliability	O
.	O
</s>
<s>
In	O
a	O
Windows	O
environment	O
,	O
one	O
domain	B-General_Concept
controller	I-General_Concept
serves	O
as	O
the	O
Primary	B-General_Concept
Domain	I-General_Concept
Controller	I-General_Concept
(	O
PDC	O
)	O
and	O
all	O
other	O
servers	O
promoted	O
to	O
domain	B-General_Concept
controller	I-General_Concept
status	O
in	O
the	O
domain	O
server	B-Application
as	O
a	O
Backup	B-General_Concept
Domain	I-General_Concept
Controller	I-General_Concept
(	O
BDC	O
)	O
.	O
</s>
<s>
In	O
Unix-based	O
environments	O
,	O
one	O
machine	O
serves	O
as	O
the	O
master	O
domain	B-General_Concept
controller	I-General_Concept
and	O
others	O
serve	O
as	O
replica	O
domain	B-General_Concept
controllers	I-General_Concept
,	O
periodically	O
replicating	O
database	O
information	O
from	O
the	O
main	O
domain	B-General_Concept
controller	I-General_Concept
and	O
storing	O
it	O
in	O
a	O
read-only	O
format	O
.	O
</s>
