<s>
Network	B-Protocol
Load	I-Protocol
Balancing	I-Protocol
Services	I-Protocol
(	O
NLBS	B-Protocol
)	O
is	O
a	O
Microsoft	O
implementation	O
of	O
clustering	B-Architecture
and	O
load	B-Application
balancing	I-Application
that	O
is	O
intended	O
to	O
provide	O
high	O
availability	O
and	O
high	O
reliability	O
,	O
as	O
well	O
as	O
high	O
scalability	O
.	O
</s>
<s>
NLBS	B-Protocol
is	O
intended	O
for	O
applications	O
with	O
relatively	O
small	O
data	O
sets	O
that	O
rarely	O
change	O
(	O
one	O
example	O
would	O
be	O
web	O
pages	O
)	O
,	O
and	O
do	O
not	O
have	O
long-running	O
in-memory	O
states	O
.	O
</s>
<s>
These	O
types	O
of	O
applications	O
are	O
called	O
stateless	O
applications	O
,	O
and	O
typically	O
include	O
Web	O
,	O
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
FTP	O
)	O
,	O
and	O
virtual	B-Application
private	I-Application
networking	I-Application
(	O
VPN	B-Application
)	O
servers	O
.	O
</s>
<s>
One	O
attractive	O
feature	O
of	O
NLBS	B-Protocol
is	O
that	O
all	O
servers	O
in	O
a	O
cluster	O
monitor	O
each	O
other	O
with	O
a	O
heartbeat	O
signal	O
,	O
so	O
there	O
is	O
no	B-Architecture
single	I-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
.	O
</s>
<s>
In	O
its	O
current	O
incarnation	O
in	O
Windows	B-Application
Server	I-Application
2003	I-Application
,	O
NLBS	B-Protocol
does	O
not	O
support	O
automatic	O
removal	O
of	O
a	O
failed	O
server	O
from	O
a	O
cluster	O
unless	O
the	O
server	O
is	O
completely	O
offline	O
,	O
or	O
if	O
its	O
NLBS	B-Protocol
service	O
is	O
stopped	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
web	O
server	O
is	O
returning	O
an	O
error	O
page	O
instead	O
of	O
correct	O
content	O
,	O
it	O
is	O
still	O
perceived	O
as	O
"	O
alive	O
"	O
by	O
NLBS	B-Protocol
.	O
</s>
<s>
Windows	B-Protocol
NT	I-Protocol
Load	I-Protocol
Balancing	I-Protocol
Service	I-Protocol
(	O
WLBS	O
)	O
is	O
a	O
feature	O
of	O
Windows	B-Device
NT	I-Device
that	O
provides	O
load	B-Application
balancing	I-Application
and	O
clustering	B-Architecture
for	O
applications	O
.	O
</s>
<s>
WLBS	O
was	O
replaced	O
by	O
Network	B-Protocol
Load	I-Protocol
Balancing	I-Protocol
Services	I-Protocol
in	O
Windows	B-Application
2000	I-Application
.	O
</s>
