<s>
Server	B-Operating_System
Message	I-Operating_System
Block	I-Operating_System
(	O
SMB	O
)	O
is	O
a	O
communication	O
protocol	O
originally	O
developed	O
in	O
1983	O
by	O
Barry	O
A	O
.	O
Feigenbaum	O
at	O
IBM	O
and	O
intended	O
to	O
provide	O
shared	B-General_Concept
access	I-General_Concept
to	O
files	B-Operating_System
and	O
printers	O
across	O
nodes	O
on	O
a	O
network	O
of	O
systems	O
running	O
IBM	O
's	O
OS/2	B-Application
.	O
</s>
<s>
It	O
also	O
provides	O
an	O
authenticated	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
IPC	O
)	O
mechanism	O
.	O
</s>
<s>
In	O
1987	O
,	O
Microsoft	O
and	O
3Com	O
implemented	O
SMB	O
in	O
LAN	B-Algorithm
Manager	I-Algorithm
for	O
OS/2	B-Application
,	O
at	O
which	O
time	O
SMB	O
used	O
the	O
NetBIOS	B-Protocol
service	O
atop	O
the	O
NetBIOS	B-Protocol
Frames	I-Protocol
protocol	I-Protocol
as	O
its	O
underlying	O
transport	O
.	O
</s>
<s>
Later	O
,	O
Microsoft	O
implemented	O
SMB	O
in	O
Windows	B-Device
NT	I-Device
3.1	I-Device
and	O
has	O
been	O
updating	O
it	O
ever	O
since	O
,	O
adapting	O
it	O
to	O
work	O
with	O
newer	O
underlying	O
transports	O
:	O
TCP/IP	B-Protocol
and	O
NetBT	O
.	O
</s>
<s>
It	O
uses	O
NTLM	O
or	O
Kerberos	B-Protocol
protocols	I-Protocol
for	O
user	O
authentication	O
.	O
</s>
<s>
In	O
1996	O
,	O
Microsoft	O
published	O
a	O
version	O
of	O
SMB	O
1.0	O
with	O
minor	O
modifications	O
under	O
the	O
Common	B-Operating_System
Internet	I-Operating_System
File	I-Operating_System
System	I-Operating_System
(	O
CIFS	B-Operating_System
)	O
moniker	O
.	O
</s>
<s>
CIFS	B-Operating_System
was	O
compatible	O
with	O
even	O
the	O
earliest	O
incarnation	O
of	O
SMB	O
,	O
including	O
LAN	B-Algorithm
Manager	I-Algorithm
's	O
.	O
</s>
<s>
It	O
supports	O
symbolic	B-Application
links	I-Application
,	O
hard	B-Application
links	I-Application
,	O
and	O
larger	O
file	O
size	O
,	O
but	O
none	O
of	O
the	O
features	O
of	O
SMB	O
2.0	O
and	O
later	O
.	O
</s>
<s>
Microsoft	O
's	O
proposal	O
,	O
however	O
,	O
remained	O
an	B-Architecture
Internet	I-Architecture
Draft	O
and	O
never	O
achieved	O
standard	O
status	O
.	O
</s>
<s>
Microsoft	O
has	O
since	O
discontinued	O
use	O
of	O
the	O
CIFS	B-Operating_System
moniker	O
but	O
continues	O
developing	O
SMB	O
and	O
making	O
subsequent	O
specifications	O
publicly	O
available	O
.	O
</s>
<s>
Server	B-Operating_System
Message	I-Operating_System
Block	I-Operating_System
(	O
SMB	O
)	O
enables	O
file	O
sharing	O
,	O
printer	B-Application
sharing	I-Application
,	O
network	O
browsing	O
,	O
and	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
through	O
named	B-Operating_System
pipes	I-Operating_System
)	O
over	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
SMB	O
serves	O
as	O
the	O
basis	O
for	O
Microsoft	O
's	O
Distributed	B-Protocol
File	I-Protocol
System	I-Protocol
implementation	O
.	O
</s>
<s>
SMB	O
relies	O
on	O
the	O
TCP	B-Protocol
and	O
IP	B-Protocol
protocols	I-Protocol
for	O
transport	O
.	O
</s>
<s>
This	O
combination	O
potentially	O
allows	O
file	O
sharing	O
over	O
complex	B-Architecture
,	I-Architecture
interconnected	I-Architecture
networks	I-Architecture
,	O
including	O
the	O
public	O
Internet	O
.	O
</s>
<s>
The	O
SMB	O
server	B-Operating_System
component	I-Operating_System
uses	O
TCP	B-Protocol
port	I-Protocol
445	O
.	O
</s>
<s>
SMB	O
originally	O
operated	O
on	O
NetBIOS	B-Protocol
over	O
IEEE	O
802.2	O
-	O
NetBIOS	B-Protocol
Frames	I-Protocol
or	O
NBF	O
-	O
and	O
over	O
IPX/SPX	B-Protocol
,	O
and	O
later	O
on	O
NetBIOS	B-Protocol
over	O
TCP/IP	B-Protocol
(	O
NetBT	O
)	O
,	O
but	O
Microsoft	O
has	O
since	O
deprecated	B-General_Concept
these	O
protocols	O
.	O
</s>
<s>
On	O
NetBT	O
,	O
the	O
server	B-Operating_System
component	I-Operating_System
uses	O
three	O
TCP	B-Protocol
or	O
UDP	B-Protocol
ports	I-Protocol
:	O
137	O
(	O
NETBIOS	B-Protocol
Name	O
Service	O
)	O
,	O
138	O
(	O
NETBIOS	B-Protocol
Datagram	O
Service	O
)	O
,	O
and	O
139	O
(	O
NETBIOS	B-Protocol
Session	O
Service	O
)	O
.	O
</s>
<s>
In	O
Microsoft	B-Application
Windows	I-Application
,	O
two	O
vaguely	O
named	O
Windows	O
services	O
implement	O
SMB	O
.	O
</s>
<s>
The	O
"	O
Server	O
"	O
service	O
(	O
ID	O
:	O
LanmanServer	O
)	O
is	O
in	O
charge	O
of	O
serving	O
shared	B-General_Concept
resources	I-General_Concept
.	O
</s>
<s>
The	O
"	O
Workstation	O
"	O
service	O
(	O
ID	O
:	O
LanmanWorkstation	O
)	O
maintains	O
the	O
computer	O
name	O
and	O
helps	O
access	O
shared	B-General_Concept
resources	I-General_Concept
on	O
other	O
computers	O
.	O
</s>
<s>
SMB	O
uses	O
the	O
Kerberos	B-Protocol
protocol	I-Protocol
to	O
authenticate	O
users	O
against	O
Active	B-Protocol
Directory	I-Protocol
on	O
Windows	B-General_Concept
domain	I-General_Concept
networks	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
4.0	I-Device
SP3	I-Device
and	O
later	O
can	O
digitally	O
sign	O
SMB	O
messages	O
to	O
prevent	O
some	O
man-in-the-middle	O
attacks	O
.	O
</s>
<s>
The	O
default	O
setting	O
for	O
Windows	B-General_Concept
domain	I-General_Concept
controllers	O
running	O
Windows	B-Application
Server	I-Application
2003	I-Application
and	O
later	O
is	O
to	O
not	O
allow	O
unsigned	O
incoming	O
connections	O
.	O
</s>
<s>
As	O
such	O
,	O
earlier	O
versions	O
of	O
Windows	O
that	O
do	O
not	O
support	O
SMB	O
signing	O
from	O
the	O
get-go	O
(	O
including	O
Windows	O
9x	O
)	O
cannot	O
connect	O
to	O
a	O
Windows	B-Application
Server	I-Application
2003	I-Application
domain	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
SMB	O
supports	O
opportunistic	O
locking	B-Operating_System
(	O
see	O
below	O
)	O
on	O
files	B-Operating_System
in	O
order	O
to	O
improve	O
performance	O
.	O
</s>
<s>
Opportunistic	O
locking	B-Operating_System
support	O
has	O
changed	O
with	O
each	O
Windows	O
Server	O
release	O
.	O
</s>
<s>
In	O
the	O
SMB	B-Operating_System
protocol	I-Operating_System
,	O
opportunistic	O
locking	B-Operating_System
is	O
a	O
mechanism	O
designed	O
to	O
improve	O
performance	O
by	O
controlling	O
caching	B-General_Concept
of	O
network	O
files	B-Operating_System
by	O
the	O
client	O
.	O
</s>
<s>
Unlike	O
traditional	O
locks	B-Operating_System
,	O
opportunistic	O
lock	O
(	O
OpLocks	B-Operating_System
)	O
are	O
not	O
strictly	O
file	B-Application
locking	I-Application
or	O
used	O
to	O
provide	O
mutual	O
exclusion	O
.	O
</s>
<s>
There	O
are	O
four	O
types	O
of	O
opportunistic	O
locks	B-Operating_System
.	O
</s>
<s>
Batch	O
Locks	B-Operating_System
Batch	O
OpLocks	B-Operating_System
were	O
created	O
originally	O
to	O
support	O
a	O
particular	O
behavior	O
of	O
DOS	B-Device
batch	O
file	O
execution	O
operation	O
in	O
which	O
the	O
file	O
is	O
opened	O
and	O
closed	O
many	O
times	O
in	O
a	O
short	O
period	O
,	O
which	O
is	O
a	O
performance	O
problem	O
.	O
</s>
<s>
Level-1	O
OpLocks	B-Operating_System
/	O
Exclusive	O
Locks	B-Operating_System
When	O
an	O
application	O
opens	O
in	O
"	O
shared	O
mode	O
"	O
a	O
file	O
hosted	O
on	O
an	O
SMB	O
server	O
which	O
is	O
not	O
opened	O
by	O
any	O
other	O
process	O
(	O
or	O
other	O
clients	O
)	O
the	O
client	O
receives	O
an	O
exclusive	O
OpLock	O
from	O
the	O
server	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
client	O
may	O
now	O
assume	O
that	O
it	O
is	O
the	O
only	O
process	O
with	O
access	O
to	O
this	O
particular	O
file	O
,	O
and	O
the	O
client	O
may	O
now	O
cache	B-General_Concept
all	O
changes	O
to	O
the	O
file	O
before	O
committing	O
it	O
to	O
the	O
server	O
.	O
</s>
<s>
Level-2	O
OpLocks	B-Operating_System
If	O
an	O
exclusive	O
OpLock	O
is	O
held	O
by	O
a	O
client	O
and	O
a	O
locked	O
file	O
is	O
opened	O
by	O
a	O
third	O
party	O
,	O
the	O
client	O
has	O
to	O
relinquish	O
its	O
exclusive	O
OpLock	O
to	O
allow	O
the	O
other	O
client	O
's	O
write/read	O
access	O
.	O
</s>
<s>
A	O
Level2	O
OpLock	O
allows	O
the	O
caching	B-General_Concept
of	O
read	O
requests	O
but	O
excludes	O
write	O
caching	B-General_Concept
.	O
</s>
<s>
Filter	O
OpLocks	B-Operating_System
Added	O
in	O
Windows	B-Device
NT	I-Device
4.0	I-Device
,	O
Filter	O
Oplocks	B-Operating_System
are	O
similar	O
to	O
Level2	O
OpLocks	B-Operating_System
but	O
prevent	O
sharing-mode	O
violations	O
between	O
file	O
open	O
and	O
lock	O
reception	O
.	O
</s>
<s>
Microsoft	O
advises	O
use	O
of	O
Filter	O
OpLocks	B-Operating_System
only	O
where	O
it	O
is	O
important	O
to	O
allow	O
multiple	O
readers	O
and	O
Level2	O
OpLocks	B-Operating_System
in	O
other	O
circumstances	O
.	O
</s>
<s>
Breaks	O
In	O
contrast	O
with	O
the	O
SMB	B-Operating_System
protocol	I-Operating_System
's	O
"	O
standard	O
"	O
behavior	O
,	O
a	O
break	O
request	O
may	O
be	O
sent	O
from	O
server	O
to	O
client	O
.	O
</s>
<s>
The	O
first	O
client	O
is	O
then	O
sent	O
an	O
OpLock	O
break	O
and	O
required	O
to	O
send	O
all	O
its	O
local	O
changes	O
(	O
in	O
case	O
of	O
batch	O
or	O
exclusive	O
OpLocks	B-Operating_System
)	O
,	O
if	O
any	O
,	O
and	O
acknowledge	O
the	O
OpLock	O
break	O
.	O
</s>
<s>
The	O
use	O
of	O
the	O
SMB	B-Operating_System
protocol	I-Operating_System
has	O
often	O
correlated	O
with	O
a	O
significant	O
increase	O
in	O
broadcast	B-Operating_System
traffic	I-Operating_System
on	O
a	O
network	O
.	O
</s>
<s>
However	O
the	O
SMB	O
itself	O
does	O
not	O
use	O
broadcasts	B-Operating_System
—	O
the	O
broadcast	B-Operating_System
problems	O
commonly	O
associated	O
with	O
SMB	O
actually	O
originate	O
with	O
the	O
NetBIOS	B-Protocol
service	O
location	O
protocol	O
.	O
</s>
<s>
By	O
default	O
,	O
a	O
Microsoft	B-Device
Windows	I-Device
NT	I-Device
4.0	I-Device
server	O
used	O
NetBIOS	B-Protocol
to	O
advertise	O
and	O
locate	O
services	O
.	O
</s>
<s>
NetBIOS	B-Protocol
functions	O
by	O
broadcasting	B-Operating_System
services	O
available	O
on	O
a	O
particular	O
host	O
at	O
regular	O
intervals	O
.	O
</s>
<s>
While	O
this	O
usually	O
makes	O
for	O
an	O
acceptable	O
default	O
in	O
a	O
network	O
with	O
a	O
smaller	O
number	O
of	O
hosts	O
,	O
increased	O
broadcast	B-Operating_System
traffic	I-Operating_System
can	O
cause	O
problems	O
as	O
the	O
number	O
of	O
hosts	O
on	O
the	O
network	O
increases	O
.	O
</s>
<s>
The	O
implementation	O
of	O
name	O
resolution	O
infrastructure	O
in	O
the	O
form	O
of	O
Windows	B-Device
Internet	I-Device
Naming	I-Device
Service	I-Device
(	O
WINS	O
)	O
or	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
resolves	O
this	O
problem	O
.	O
</s>
<s>
WINS	O
was	O
a	O
proprietary	O
implementation	O
used	O
with	O
Windows	B-Device
NT	I-Device
4.0	I-Device
networks	O
,	O
but	O
brought	O
about	O
its	O
own	O
issues	O
and	O
complexities	O
in	O
the	O
design	O
and	O
maintenance	O
of	O
a	O
Microsoft	O
network	O
.	O
</s>
<s>
Since	O
the	O
release	O
of	O
Windows	B-Application
2000	I-Application
,	O
the	O
use	O
of	O
WINS	O
for	O
name	O
resolution	O
has	O
been	O
deprecated	B-General_Concept
by	O
Microsoft	O
,	O
with	O
hierarchical	O
Dynamic	B-Protocol
DNS	I-Protocol
now	O
configured	O
as	O
the	O
default	O
name	O
resolution	O
protocol	O
for	O
all	O
Windows	B-Application
operating	I-Application
systems	I-Application
.	O
</s>
<s>
Resolution	O
of	O
(	O
short	O
)	O
NetBIOS	B-Protocol
names	O
by	O
DNS	B-Protocol
requires	O
that	O
a	O
DNS	B-Protocol
client	O
expand	O
short	O
names	O
,	O
usually	O
by	O
appending	O
a	O
connection-specific	O
DNS	B-Protocol
suffix	O
to	O
its	O
DNS	B-Protocol
lookup	O
queries	O
.	O
</s>
<s>
Further	O
,	O
Microsoft	O
DNS	B-Protocol
servers	O
can	O
forward	O
name	O
resolution	O
requests	O
to	O
legacy	O
WINS	B-Device
servers	I-Device
in	O
order	O
to	O
support	O
name	O
resolution	O
integration	O
with	O
legacy	O
(	O
pre-Windows	O
2000	O
)	O
environments	O
that	O
do	O
not	O
support	O
DNS	B-Protocol
.	O
</s>
<s>
Network	B-Architecture
designers	I-Architecture
have	O
found	O
that	O
latency	O
has	O
a	O
significant	O
impact	O
on	O
the	O
performance	O
of	O
the	O
SMB	O
1.0	O
protocol	O
,	O
that	O
it	O
performs	O
more	O
poorly	O
than	O
other	O
protocols	O
like	O
FTP	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
a	O
VPN	B-Application
connection	O
over	O
the	O
Internet	O
will	O
often	O
introduce	O
network	O
latency	O
.	O
</s>
<s>
Microsoft	O
has	O
explained	O
that	O
performance	O
issues	O
come	O
about	O
primarily	O
because	O
SMB	O
1.0	O
is	O
a	O
block-level	O
rather	O
than	O
a	O
streaming	O
protocol	O
,	O
that	O
was	O
originally	O
designed	O
for	O
small	O
LANs	B-General_Concept
;	O
it	O
has	O
a	O
block	O
size	O
that	O
is	O
limited	O
to	O
64K	O
,	O
SMB	O
signing	O
creates	O
an	O
additional	O
overhead	O
and	O
the	O
TCP	B-Protocol
window	I-Protocol
size	I-Protocol
is	O
not	O
optimized	O
for	O
WAN	O
links	O
.	O
</s>
<s>
Solutions	O
to	O
this	O
problem	O
include	O
the	O
updated	O
SMB	O
2.0	O
protocol	O
,	O
Offline	O
Files	B-Operating_System
,	O
TCP	B-Protocol
window	I-Protocol
scaling	I-Protocol
and	O
WAN	B-Protocol
optimization	I-Protocol
devices	O
from	O
various	O
network	O
vendors	O
that	O
cache	B-General_Concept
and	O
optimize	O
SMB	O
1.0	O
and	O
2.0	O
.	O
</s>
<s>
Barry	O
Feigenbaum	O
originally	O
designed	O
SMB	O
at	O
IBM	O
in	O
early	O
1983	O
with	O
the	O
aim	O
of	O
turning	O
DOS	B-Device
INT	B-Application
21h	I-Application
local	O
file	O
access	O
into	O
a	O
networked	O
file	O
system	O
.	O
</s>
<s>
Microsoft	O
made	O
considerable	O
modifications	O
to	O
the	O
most	O
commonly	O
used	O
version	O
and	O
implemented	O
"	O
SMB	O
1.0/CIFS	O
Server	O
"	O
,	O
the	O
SMB	B-Operating_System
protocol	I-Operating_System
,	O
in	O
the	O
LAN	B-Algorithm
Manager	I-Algorithm
operating	O
system	O
it	O
had	O
started	O
developing	O
for	O
OS/2	B-Application
with	O
3Com	O
around	O
1990	O
,	O
and	O
continued	O
to	O
add	O
features	O
to	O
the	O
protocol	O
in	O
Windows	O
for	O
Workgroups	O
(	O
)	O
and	O
in	O
later	O
versions	O
of	O
Windows	O
.	O
</s>
<s>
LAN	B-Algorithm
Manager	I-Algorithm
authentication	O
was	O
implemented	O
based	O
on	O
the	O
original	O
legacy	O
SMB	O
specification	O
's	O
requirement	O
to	O
use	O
IBM	O
"	O
LAN	B-Algorithm
Manager	I-Algorithm
"	O
passwords	O
,	O
but	O
implemented	O
DES	B-Algorithm
in	O
a	O
flawed	O
manner	O
that	O
allowed	O
passwords	O
to	O
be	O
cracked	O
.	O
</s>
<s>
Later	O
,	O
Kerberos	B-Protocol
authentication	O
was	O
also	O
added	O
.	O
</s>
<s>
The	O
Windows	B-General_Concept
domain	I-General_Concept
logon	O
protocols	O
initially	O
used	O
40-bit	O
encryption	O
outside	O
of	O
the	O
United	O
States	O
,	O
because	O
of	O
export	O
restrictions	O
on	O
stronger	O
128-bit	O
encryption	O
(	O
subsequently	O
lifted	O
in	O
1996	O
when	O
President	O
Bill	O
Clinton	O
signed	O
Executive	O
Order	O
13026	O
)	O
.	O
</s>
<s>
SMB	O
1.0	O
(	O
or	O
SMB1	O
)	O
was	O
originally	O
designed	O
to	O
run	O
on	O
NetBIOS	B-Protocol
Frames	I-Protocol
(	O
NetBIOS	B-Protocol
over	O
IEEE	O
802.2	O
)	O
.	O
</s>
<s>
Since	O
then	O
,	O
it	O
has	O
been	O
adapted	O
to	O
NetBIOS	B-Protocol
over	O
IPX/SPX	B-Protocol
(	O
NBX	O
)	O
,	O
and	O
NetBIOS	B-Protocol
over	O
TCP/IP	B-Protocol
(	O
NetBT	O
)	O
.	O
</s>
<s>
Also	O
,	O
since	O
Windows	B-Application
2000	I-Application
,	O
SMB	O
runs	O
on	O
TCP	B-Protocol
using	O
TCP	B-Protocol
port	I-Protocol
445	O
,	O
a	O
feature	O
known	O
as	O
"	O
direct	O
host	O
SMB	O
"	O
.	O
</s>
<s>
There	O
is	O
still	O
a	O
thin	O
layer	O
(	O
similar	O
to	O
the	O
Session	O
Message	O
packet	O
of	O
NetBT	O
's	O
Session	O
Service	O
)	O
between	O
SMB	O
and	O
TCP	B-Protocol
.	O
</s>
<s>
Windows	B-Application
Server	I-Application
2003	I-Application
,	O
and	O
legacy	O
NAS	B-Application
devices	O
use	O
SMB1	O
natively	O
.	O
</s>
<s>
SMB1	O
is	O
an	O
extremely	O
chatty	O
protocol	O
,	O
which	O
is	O
not	O
such	O
an	O
issue	O
on	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
with	O
low	O
latency	O
.	O
</s>
<s>
One	O
approach	O
to	O
mitigating	O
the	O
inefficiencies	O
in	O
the	O
protocol	O
is	O
to	O
use	O
WAN	B-Protocol
optimization	I-Protocol
products	O
such	O
as	O
those	O
provided	O
by	O
Riverbed	O
,	O
Silver	O
Peak	O
,	O
or	O
Cisco	O
.	O
</s>
<s>
This	O
includes	O
upgrading	O
both	O
NAS	B-Application
devices	O
as	O
well	O
as	O
Windows	B-Application
Server	I-Application
2003	I-Application
.	O
</s>
<s>
The	O
most	O
effective	O
method	O
to	O
identify	O
SMB1	O
traffic	O
is	O
with	O
a	O
network	O
analyzer	O
tool	O
,	O
such	O
as	O
Wireshark	B-Language
.	O
</s>
<s>
Microsoft	O
also	O
provides	O
an	O
auditing	O
tool	O
in	O
Windows	B-Device
Server	I-Device
2016	I-Device
to	O
track	O
down	O
devices	O
that	O
use	O
SMB1	O
.	O
</s>
<s>
Microsoft	O
has	O
marked	O
SMB1	O
as	O
deprecated	B-General_Concept
in	O
June	O
2013	O
.	O
</s>
<s>
Windows	B-Device
Server	I-Device
2016	I-Device
and	O
Windows	B-Operating_System
10	I-Operating_System
version	O
1709	O
do	O
not	O
have	O
SMB1	O
installed	O
by	O
default	O
.	O
</s>
<s>
In	O
1996	O
,	O
when	O
Sun	O
Microsystems	O
announced	O
WebNFS	B-Protocol
,	O
Microsoft	O
launched	O
an	O
initiative	O
to	O
rename	O
SMB	O
to	O
Common	B-Operating_System
Internet	I-Operating_System
File	I-Operating_System
System	I-Operating_System
(	O
CIFS	B-Operating_System
)	O
and	O
added	O
more	O
features	O
,	O
including	O
support	O
for	O
symbolic	B-Application
links	I-Application
,	O
hard	B-Application
links	I-Application
,	O
larger	O
file	O
sizes	O
,	O
and	O
an	O
initial	O
attempt	O
at	O
supporting	O
direct	O
connections	O
over	O
TCP	B-Protocol
port	I-Protocol
445	O
without	O
requiring	O
NetBIOS	B-Protocol
as	O
a	O
transport	O
(	O
a	O
largely	O
experimental	O
effort	O
that	O
required	O
further	O
refinement	O
)	O
.	O
</s>
<s>
Microsoft	O
introduced	O
a	O
new	O
version	O
of	O
the	O
protocol	O
(	O
SMB	O
2.0	O
or	O
SMB2	O
)	O
in	O
2006	O
with	O
Windows	B-Application
Vista	I-Application
and	O
Windows	B-Device
Server	I-Device
2008	I-Device
.	O
</s>
<s>
It	O
has	O
mechanisms	O
for	O
pipelining	B-General_Concept
,	O
that	O
is	O
,	O
sending	O
additional	O
requests	O
before	O
the	O
response	O
to	O
a	O
previous	O
request	O
arrives	O
,	O
thereby	O
improving	O
performance	O
over	O
high-latency	O
links	O
.	O
</s>
<s>
It	O
also	O
introduces	O
the	O
notion	O
of	O
"	O
durable	O
file	B-Application
handles	I-Application
"	O
:	O
these	O
allow	O
a	O
connection	O
to	O
an	O
SMB	O
server	O
to	O
survive	O
brief	O
network	O
outages	O
,	O
as	O
are	O
typical	O
in	O
a	O
wireless	O
network	O
,	O
without	O
having	O
to	O
incur	O
the	O
overhead	O
of	O
re-negotiating	O
a	O
new	O
session	O
.	O
</s>
<s>
SMB2	O
includes	O
support	O
for	O
symbolic	B-Application
links	I-Application
.	O
</s>
<s>
Other	O
improvements	O
include	O
caching	B-General_Concept
of	O
file	O
properties	O
,	O
improved	O
message	O
signing	O
with	O
HMAC	B-Algorithm
SHA-256	B-Algorithm
hashing	O
algorithm	O
and	O
better	O
scalability	O
by	O
increasing	O
the	O
number	O
of	O
users	O
,	O
shares	O
and	O
open	O
files	B-Operating_System
per	O
server	O
among	O
others	O
.	O
</s>
<s>
SMB1	O
continues	O
in	O
use	O
for	O
connections	O
with	O
older	O
versions	O
of	O
Windows	O
,	O
as	O
well	O
various	O
vendors	O
 '	O
NAS	B-Application
solutions	O
.	O
</s>
<s>
When	O
SMB2	O
was	O
introduced	O
it	O
brought	O
a	O
number	O
of	O
benefits	O
over	O
SMB1	O
for	O
third	O
party	O
implementers	O
of	O
SMB	B-Operating_System
protocols	I-Operating_System
.	O
</s>
<s>
SMB1	O
,	O
originally	O
designed	O
by	O
IBM	O
,	O
was	O
reverse	O
engineered	O
,	O
and	O
later	O
became	O
part	O
of	O
a	O
wide	O
variety	O
of	O
non-Windows	O
operating	O
systems	O
such	O
as	O
Xenix	B-Application
,	O
OS/2	B-Application
and	O
VMS	B-Operating_System
(	O
Pathworks	B-Application
)	O
.	O
</s>
<s>
X/Open	O
standardized	O
it	O
partially	O
;	O
Microsoft	O
had	O
submitted	O
Internet-Drafts	O
describing	O
SMB2	O
to	O
the	O
IETF	O
,	O
partly	O
in	O
response	O
to	O
formal	O
IETF	O
standardization	O
of	O
version	O
4	O
of	O
the	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
in	O
December	O
2000	O
as	O
IETF	O
RFC	O
3010	O
;	O
however	O
,	O
those	O
SMB-related	O
Internet-Drafts	O
expired	O
without	O
achieving	O
any	O
IETF	O
standards-track	O
approval	O
or	O
any	O
other	O
IETF	O
endorsement	O
.	O
</s>
<s>
Apple	O
migrated	O
to	O
SMB2	O
(	O
from	O
their	O
own	O
Apple	B-Protocol
Filing	I-Protocol
Protocol	I-Protocol
,	O
now	O
legacy	O
)	O
starting	O
with	O
OS	B-Operating_System
X	I-Operating_System
10.9	I-Operating_System
"	I-Operating_System
Mavericks	I-Operating_System
"	I-Operating_System
.	O
</s>
<s>
MacOS	B-Application
also	O
has	O
supported	O
the	O
IETF	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
NFS	O
)	O
for	O
many	O
years	O
(	O
and	O
continues	O
to	O
do	O
so	O
as	O
of	O
2021	O
)	O
.	O
</s>
<s>
The	O
Linux	B-Operating_System
kernel	I-Operating_System
's	O
CIFS	B-Operating_System
client	O
file	O
system	O
has	O
SMB2	O
support	O
since	O
version	O
3.7	O
.	O
</s>
<s>
SMB	O
2.1	O
,	O
introduced	O
with	O
Windows	O
7	O
and	O
Server	B-Device
2008	I-Device
R2	O
,	O
introduced	O
minor	O
performance	O
enhancements	O
with	O
a	O
new	O
opportunistic	O
locking	B-Operating_System
mechanism	O
.	O
</s>
<s>
SMB	O
3.0	O
(	O
previously	O
named	O
SMB	O
2.2	O
)	O
was	O
introduced	O
with	O
Windows	B-Application
8	I-Application
and	O
Windows	B-Device
Server	I-Device
2012	I-Device
.	O
</s>
<s>
It	O
brought	O
several	O
significant	O
changes	O
that	O
are	O
intended	O
to	O
add	O
functionality	O
and	O
improve	O
SMB2	O
performance	O
,	O
notably	O
in	O
virtualized	O
data	B-Operating_System
centers	I-Operating_System
:	O
</s>
<s>
It	O
also	O
introduces	O
several	O
security	O
enhancements	O
,	O
such	O
as	O
end-to-end	O
encryption	O
and	O
a	O
new	O
AES	B-Algorithm
based	O
signing	O
algorithm	O
.	O
</s>
<s>
SMB	O
3.0.2	O
(	O
known	O
as	O
3.02	O
at	O
the	O
time	O
)	O
was	O
introduced	O
with	O
Windows	O
8.1	O
and	O
Windows	B-Device
Server	I-Device
2012	I-Device
R2	O
;	O
in	O
those	O
and	O
later	O
releases	O
,	O
the	O
earlier	O
SMB	O
version	O
1	O
can	O
be	O
optionally	O
disabled	O
to	O
increase	O
security	O
.	O
</s>
<s>
SMB	O
3.1.1	O
was	O
introduced	O
with	O
Windows	B-Operating_System
10	I-Operating_System
and	O
Windows	B-Device
Server	I-Device
2016	I-Device
.	O
</s>
<s>
This	O
version	O
supports	O
AES-128	B-Algorithm
GCM	B-Algorithm
encryption	O
in	O
addition	O
to	O
AES-128	B-Algorithm
CCM	B-Algorithm
encryption	O
added	O
in	O
SMB3	O
,	O
and	O
implements	O
pre-authentication	O
integrity	O
check	O
using	O
SHA-512	B-Algorithm
hash	O
.	O
</s>
<s>
In	O
1991	O
,	O
Andrew	O
Tridgell	O
started	O
the	O
development	O
of	O
Samba	O
,	O
a	O
free-software	B-Application
re-implementation	O
(	O
using	O
reverse	O
engineering	O
)	O
of	O
the	O
SMB/CIFS	B-Operating_System
networking	O
protocol	O
for	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
initially	O
to	O
implement	O
an	O
SMB	O
server	O
to	O
allow	O
PC	O
clients	O
running	O
the	O
DEC	O
Pathworks	B-Application
client	O
to	O
access	O
files	B-Operating_System
on	O
SunOS	B-Operating_System
machines	O
.	O
</s>
<s>
Because	O
of	O
the	O
importance	O
of	O
the	O
SMB	B-Operating_System
protocol	I-Operating_System
in	O
interacting	O
with	O
the	O
widespread	O
Microsoft	B-Application
Windows	I-Application
platform	O
,	O
Samba	O
became	O
a	O
popular	O
free	B-Application
software	I-Application
implementation	O
of	O
a	O
compatible	O
SMB	O
client	O
and	O
server	O
to	O
allow	O
non-Windows	O
operating	O
systems	O
,	O
such	O
as	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
to	O
interoperate	O
with	O
Windows	O
.	O
</s>
<s>
As	O
of	O
version	O
3	O
(	O
2003	O
)	O
,	O
Samba	O
provides	O
file	O
and	O
print	O
services	O
for	O
Microsoft	B-Application
Windows	I-Application
clients	O
and	O
can	O
integrate	O
with	O
a	O
Windows	B-Device
NT	I-Device
4.0	I-Device
server	O
domain	O
,	O
either	O
as	O
a	O
Primary	B-General_Concept
Domain	I-General_Concept
Controller	I-General_Concept
(	O
PDC	O
)	O
or	O
as	O
a	O
domain	O
member	O
.	O
</s>
<s>
Samba4	O
installations	O
can	O
act	O
as	O
an	O
Active	B-Protocol
Directory	I-Protocol
domain	B-General_Concept
controller	I-General_Concept
or	O
member	O
server	O
,	O
at	O
Windows	B-Device
2008	I-Device
domain	O
and	O
forest	B-Protocol
functional	O
levels	O
.	O
</s>
<s>
Package	O
managers	O
in	O
Linux	B-Operating_System
distributions	O
can	O
search	O
for	O
the	O
cifs-utils	O
package	O
.	O
</s>
<s>
NSMB	O
(	O
Netsmb	O
and	O
SMBFS	B-Operating_System
)	O
is	O
a	O
family	O
of	O
in-kernel	O
SMB	O
client	O
implementations	O
in	O
BSD	O
operating	O
systems	O
.	O
</s>
<s>
It	O
was	O
first	O
contributed	O
to	O
FreeBSD	O
4.4	O
by	O
Boris	O
Popov	O
,	O
and	O
is	O
now	O
found	O
in	O
a	O
wide	O
range	O
of	O
other	O
BSD	O
systems	O
including	O
NetBSD	B-Device
and	O
macOS	B-Application
.	O
</s>
<s>
The	O
macOS	B-Application
version	O
of	O
NSMB	O
is	O
notable	O
for	O
its	O
now-common	O
scheme	O
of	O
representing	O
symlinks	B-Application
.	O
</s>
<s>
This	O
"	O
Minshall-French	O
"	O
format	O
shows	O
symlinks	B-Application
as	O
textual	O
files	B-Operating_System
with	O
a	O
extension	O
and	O
a	O
magic	O
number	O
,	O
always	O
1067	O
bytes	O
long	O
.	O
</s>
<s>
This	O
format	O
is	O
also	O
used	O
for	O
storing	O
symlinks	B-Application
on	O
native	O
SMB	O
servers	O
or	O
unsupported	O
filesystems	O
.	O
</s>
<s>
MoSMB	O
is	O
a	O
proprietary	O
SMB	O
implementation	O
for	O
Linux	B-Operating_System
and	O
other	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
developed	O
by	O
Ryussi	O
Technologies	O
.	O
</s>
<s>
Fusion	O
File	O
Share	O
by	O
Tuxera	O
is	O
a	O
proprietary	O
SMB	O
server	O
implementation	O
developed	O
by	O
Tuxera	O
that	O
can	O
be	O
run	O
either	O
in	O
kernel	B-Operating_System
or	O
user	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
It	O
supports	O
SMB	O
3.1.1	O
and	O
all	O
previous	O
versions	O
,	O
additionally	O
advanced	O
SMB	O
features	O
like	O
continuous	O
availability	O
(	O
persistent	O
handles	O
)	O
scale-out	O
,	O
RDMA	B-General_Concept
(	O
SMB	O
Direct	O
)	O
,	O
SMB	O
multichannel	O
,	O
transparent	O
compression	O
,	O
shadow	O
copy	O
.	O
</s>
<s>
Likewise	O
developed	O
a	O
CIFS/SMB	B-Operating_System
implementation	O
(	O
versions	O
1.0	O
,	O
2.0	O
,	O
2.1	O
and	O
NFS	O
3.0	O
)	O
in	O
2009	O
that	O
provided	O
a	O
multiprotocol	O
,	O
identity-aware	O
platform	O
for	O
network	O
access	O
to	O
files	B-Operating_System
used	O
in	O
OEM	O
storage	O
products	O
built	O
on	O
Linux/Unix	O
based	O
devices	O
.	O
</s>
<s>
The	O
platform	O
could	O
be	O
used	O
for	O
traditional	O
NAS	B-Application
,	O
Cloud	O
Gateway	O
,	O
and	O
Cloud	O
Caching	B-General_Concept
devices	O
for	O
providing	O
secure	O
access	O
to	O
files	B-Operating_System
across	O
a	O
network	O
.	O
</s>
<s>
CIFSD	B-Application
is	O
an	O
open	O
source	O
in-kernel	O
CIFS/SMB	B-Operating_System
server	O
implementation	O
for	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
It	O
has	O
the	O
following	O
advantages	O
over	O
user-space	B-Operating_System
implementations	O
:	O
it	O
provides	O
better	O
performance	O
,	O
and	O
it	O
makes	O
it	O
easier	O
to	O
implement	O
some	O
features	O
such	O
as	O
SMB	O
Direct	O
.	O
</s>
<s>
Other	O
vendors	O
 '	O
security	O
vulnerabilities	O
lie	O
primarily	O
in	O
a	O
lack	O
of	O
support	O
for	O
newer	O
authentication	B-Protocol
protocols	I-Protocol
like	O
NTLMv2	O
and	O
Kerberos	B-Protocol
in	O
favor	O
of	O
protocols	O
like	O
NTLMv1	O
,	O
LanMan	O
,	O
or	O
plaintext	O
passwords	O
.	O
</s>
