<s>
Flexible	B-General_Concept
Single	I-General_Concept
Master	I-General_Concept
Operations	I-General_Concept
(	O
FSMO	B-General_Concept
,	O
F	O
is	O
sometimes	O
"	O
floating	O
"	O
;	O
pronounced	O
Fiz-mo	O
)	O
,	O
or	O
just	O
single	O
master	O
operation	O
or	O
operations	B-General_Concept
master	I-General_Concept
,	O
is	O
a	O
feature	O
of	O
Microsoft	O
's	O
Active	B-Protocol
Directory	I-Protocol
(	O
AD	O
)	O
.	O
</s>
<s>
As	O
of	O
2005	O
,	O
the	O
term	O
FSMO	B-General_Concept
has	O
been	O
deprecated	O
in	O
favour	O
of	O
operations	B-General_Concept
masters	I-General_Concept
.	O
</s>
<s>
FSMO	B-General_Concept
is	O
a	O
specialized	O
domain	B-Protocol
controller	I-Protocol
(	O
DC	O
)	O
set	O
of	O
tasks	O
,	O
used	O
where	O
standard	O
data	O
transfer	O
and	O
update	O
methods	O
are	O
inadequate	O
.	O
</s>
<s>
AD	O
normally	O
relies	O
on	O
multiple	O
peer	O
DCs	O
,	O
each	O
with	O
a	O
copy	O
of	O
the	O
AD	O
database	O
,	O
being	O
synchronized	O
by	O
multi-master	B-Operating_System
replication	I-Operating_System
.	O
</s>
<s>
The	O
tasks	O
which	O
are	O
not	O
suited	O
to	O
multi-master	B-Operating_System
replication	I-Operating_System
and	O
are	O
viable	O
only	O
with	O
a	O
single-master	O
database	O
are	O
the	O
FSMOs	O
.	O
</s>
<s>
The	O
PDC	O
Emulator	O
(	O
Primary	O
Domain	B-Protocol
Controller	I-Protocol
)	O
-	O
This	O
role	O
is	O
the	O
most	O
used	O
of	O
all	O
FSMO	B-General_Concept
roles	O
and	O
has	O
the	O
widest	O
range	O
of	O
functions	O
.	O
</s>
<s>
The	O
domain	B-Protocol
controller	I-Protocol
that	O
holds	O
the	O
PDC	O
Emulator	O
role	O
is	O
crucial	O
in	O
a	O
mixed	O
environment	O
where	O
Windows	O
NT	O
4.0	O
BDCs	O
are	O
still	O
present	O
.	O
</s>
<s>
Even	O
if	O
all	O
Windows	O
NT	O
4.0	O
domain	B-Protocol
controllers	I-Protocol
have	O
been	O
migrated	O
to	O
Windows	O
2000	O
or	O
later	O
,	O
the	O
domain	B-Protocol
controller	I-Protocol
that	O
holds	O
the	O
PDC	O
Emulator	O
role	O
still	O
does	O
a	O
lot	O
.	O
</s>
<s>
The	O
PDC	O
Emulator	O
is	O
the	O
domain	O
source	O
for	O
time	O
synchronization	O
for	O
all	O
other	O
domain	B-Protocol
controllers	I-Protocol
;	O
in	O
a	O
multi-domain	O
forest	O
,	O
the	O
PDC	O
Emulator	O
in	O
each	O
domain	O
synchronizes	O
to	O
the	O
forest	O
root	O
PDC	O
Emulator	O
.	O
</s>
<s>
All	O
other	O
domain	O
member	O
computers	O
synchronize	O
to	O
their	O
respective	O
domain	B-Protocol
controllers	I-Protocol
.	O
</s>
<s>
It	O
is	O
critically	O
important	O
that	O
computer	O
clocks	O
are	O
synchronized	O
across	O
the	O
forest	O
because	O
excessive	O
clock	O
skew	O
causes	O
Kerberos	B-Protocol
authentication	O
to	O
fail	O
.	O
</s>
<s>
The	O
RID	B-General_Concept
Master	O
-	O
(	O
Relative	B-General_Concept
ID	I-General_Concept
)	O
This	O
FSMO	B-General_Concept
role	O
owner	O
is	O
the	O
single	O
DC	O
responsible	O
for	O
processing	O
RID	B-General_Concept
Pool	O
requests	O
from	O
all	O
DCs	O
within	O
a	O
given	O
domain	O
.	O
</s>
<s>
This	O
SID	O
consists	O
of	O
a	O
domain	O
SID	O
(	O
the	O
same	O
for	O
all	O
SIDs	O
created	O
in	O
a	O
domain	O
)	O
and	O
a	O
relative	B-General_Concept
ID	I-General_Concept
(	O
RID	B-General_Concept
)	O
that	O
is	O
unique	O
for	O
each	O
security	O
principal	O
SID	O
created	O
in	O
a	O
domain	O
.	O
</s>
<s>
When	O
a	O
DC	O
's	O
allocated	O
RID	B-General_Concept
pool	O
falls	O
below	O
a	O
threshold	O
,	O
that	O
DC	O
issues	O
a	O
request	O
for	O
additional	O
RIDs	O
to	O
the	O
domain	O
's	O
RID	B-General_Concept
Master	O
FSMO	B-General_Concept
role	O
owner	O
,	O
the	O
RID	B-General_Concept
Master	O
FSMO	B-General_Concept
role	O
owner	O
responds	O
to	O
the	O
request	O
by	O
retrieving	O
RIDs	O
from	O
the	O
domain	O
's	O
unallocated	O
RID	B-General_Concept
pool	O
and	O
assigns	O
them	O
to	O
the	O
pool	O
of	O
the	O
requesting	O
DC	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
Active	B-Protocol
Directory	I-Protocol
deployment	O
has	O
only	O
a	O
single	O
domain	O
,	O
then	O
the	O
Infrastructure	O
Master	O
role	O
does	O
no	O
work	O
at	O
all	O
,	O
and	O
even	O
in	O
a	O
multi-domain	O
environment	O
it	O
is	O
rarely	O
used	O
except	O
when	O
complex	O
user	O
administration	O
tasks	O
are	O
performed	O
.	O
</s>
<s>
The	O
Schema	O
Master	O
-	O
The	O
purpose	O
of	O
this	O
role	O
is	O
to	O
replicate	O
schema	O
changes	O
to	O
all	O
other	O
domain	B-Protocol
controllers	I-Protocol
in	O
the	O
forest	O
.	O
</s>
<s>
Since	O
the	O
schema	O
of	O
Active	B-Protocol
Directory	I-Protocol
is	O
rarely	O
changed	O
,	O
however	O
,	O
the	O
Schema	O
Master	O
role	O
will	O
rarely	O
do	O
any	O
work	O
.	O
</s>
<s>
This	O
role	O
is	O
typically	O
involved	O
in	O
the	O
deployment	O
of	O
Exchange	O
Server	O
and	O
Skype	O
for	O
Business	O
Server	O
,	O
as	O
well	O
as	O
domain	B-Protocol
controllers	I-Protocol
from	O
one	O
version	O
to	O
another	O
version	O
,	O
as	O
all	O
of	O
these	O
situations	O
involve	O
making	O
changes	O
to	O
the	O
Active	B-Protocol
Directory	I-Protocol
schema	I-Protocol
.	O
</s>
<s>
The	O
Domain	O
Naming	O
Master	O
-	O
The	O
other	O
forest-specific	O
FSMO	B-General_Concept
role	O
is	O
the	O
Domain	O
Naming	O
Master	O
,	O
and	O
this	O
role	O
also	O
resides	O
in	O
the	O
forest	O
root	O
domain	O
.	O
</s>
<s>
Failure	O
of	O
this	O
role	O
to	O
function	O
correctly	O
can	O
prevent	O
the	O
addition	O
of	O
a	O
new	O
child	O
domain	O
or	O
new	O
domain	B-Protocol
tree	I-Protocol
.	O
</s>
<s>
By	O
default	O
AD	O
assigns	O
all	O
operations	B-General_Concept
master	I-General_Concept
roles	O
to	O
the	O
first	O
DC	O
created	O
in	O
a	O
forest	O
.	O
</s>
<s>
To	O
provide	O
fault	O
tolerance	O
,	O
there	O
should	O
be	O
multiple	O
domain	B-Protocol
controllers	I-Protocol
available	O
within	O
each	O
domain	O
of	O
the	O
Forest	O
.	O
</s>
<s>
If	O
new	O
domains	O
are	O
created	O
in	O
the	O
forest	O
,	O
the	O
first	O
DC	O
in	O
a	O
new	O
domain	O
holds	O
all	O
of	O
the	O
domain-wide	O
FSMO	B-General_Concept
roles	O
.	O
</s>
<s>
This	O
is	O
not	O
a	O
satisfactory	O
position	O
if	O
the	O
domain	O
has	O
a	O
large	O
number	O
of	O
domain	B-Protocol
controllers	I-Protocol
.	O
</s>
<s>
Microsoft	O
recommends	O
the	O
careful	O
division	O
of	O
FSMO	B-General_Concept
roles	O
,	O
with	O
standby	O
DCs	O
ready	O
to	O
take	O
over	O
each	O
role	O
.	O
</s>
<s>
The	O
PDC	O
emulator	O
and	O
the	O
RID	B-General_Concept
master	O
should	O
be	O
on	O
the	O
same	O
DC	O
,	O
if	O
possible	O
.	O
</s>
<s>
When	O
a	O
FSMO	B-General_Concept
role	O
is	O
transferred	O
to	O
a	O
different	O
DC	O
,	O
the	O
original	O
FSMO	B-General_Concept
holder	O
and	O
the	O
new	O
FSMO	B-General_Concept
holder	O
communicate	O
to	O
ensure	O
no	O
data	O
is	O
lost	O
during	O
the	O
transfer	O
.	O
</s>
<s>
If	O
the	O
original	O
FSMO	B-General_Concept
holder	O
experienced	O
an	O
unrecoverable	O
failure	O
,	O
another	O
DC	O
can	O
be	O
made	O
to	O
"	O
seize	O
"	O
the	O
lost	O
roles	O
;	O
however	O
,	O
there	O
is	O
a	O
risk	O
of	O
data	O
loss	O
because	O
of	O
the	O
lack	O
of	O
communications	O
.	O
</s>
<s>
Seizing	O
roles	O
from	O
a	O
domain	B-Protocol
controller	I-Protocol
instead	O
of	O
transferring	O
it	O
prevents	O
that	O
domain	B-Protocol
controller	I-Protocol
from	O
hosting	O
that	O
FSMO	B-General_Concept
role	O
again	O
,	O
except	O
for	O
the	O
PDC	O
Emulator	O
and	O
Infrastructure	O
Master	O
Operation	O
roles	O
.	O
</s>
<s>
Corruption	O
can	O
occur	O
within	O
Active	B-Protocol
Directory	I-Protocol
.	O
</s>
<s>
FSMO	B-General_Concept
roles	O
can	O
be	O
easily	O
moved	O
between	O
DCs	O
using	O
the	O
AD	O
snap-ins	B-Application
to	O
the	O
MMC	B-Application
or	O
using	O
ntdsutil	O
,	O
which	O
is	O
a	O
command	O
line-based	O
tool	O
.	O
</s>
<s>
Certain	O
FSMO	B-General_Concept
roles	O
depend	O
on	O
the	O
DC	O
being	O
a	O
Global	B-Protocol
Catalog	I-Protocol
(	O
GC	O
)	O
server	O
as	O
well	O
.	O
</s>
<s>
When	O
a	O
Forest	O
is	O
initially	O
created	O
,	O
the	O
first	O
Domain	B-Protocol
Controller	I-Protocol
is	O
a	O
Global	B-Protocol
Catalog	I-Protocol
server	O
by	O
default	O
.	O
</s>
<s>
The	O
Global	B-Protocol
Catalog	I-Protocol
provides	O
several	O
functions	O
.	O
</s>
<s>
Often	O
all	O
domain	B-Protocol
controllers	I-Protocol
are	O
also	O
global	B-Protocol
catalog	I-Protocol
servers	O
.	O
</s>
<s>
If	O
this	O
is	O
not	O
the	O
case	O
,	O
the	O
Infrastructure	O
Master	O
role	O
must	O
not	O
be	O
housed	O
on	O
a	O
domain	B-Protocol
controller	I-Protocol
which	O
also	O
houses	O
a	O
copy	O
of	O
the	O
global	B-Protocol
catalog	I-Protocol
in	O
a	O
multi-domain	O
forest	O
,	O
as	O
the	O
combination	O
of	O
these	O
two	O
roles	O
on	O
the	O
same	O
host	O
will	O
cause	O
unexpected	O
(	O
and	O
potentially	O
damaging	O
)	O
behaviour	O
in	O
a	O
multi-domain	O
environment	O
.	O
</s>
