<s>
Simple	B-Protocol
Network	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
(	O
SNMP	B-Protocol
)	O
is	O
an	O
Internet	O
Standard	O
protocol	O
for	O
collecting	O
and	O
organizing	O
information	O
about	O
managed	O
devices	O
on	O
IP	B-Protocol
networks	I-Protocol
and	O
for	O
modifying	O
that	O
information	O
to	O
change	O
device	O
behaviour	O
.	O
</s>
<s>
Devices	O
that	O
typically	O
support	O
SNMP	B-Protocol
include	O
cable	B-Device
modems	I-Device
,	O
routers	B-Protocol
,	O
switches	B-Protocol
,	O
servers	O
,	O
workstations	O
,	O
printers	O
,	O
and	O
more	O
.	O
</s>
<s>
SNMP	B-Protocol
is	O
widely	O
used	O
in	O
network	O
management	O
for	O
network	O
monitoring	O
.	O
</s>
<s>
SNMP	B-Protocol
exposes	O
management	O
data	O
in	O
the	O
form	O
of	O
variables	O
on	O
the	O
managed	O
systems	O
organized	O
in	O
a	O
management	O
information	O
base	O
(	O
MIB	O
)	O
which	O
describe	O
the	O
system	O
status	O
and	O
configuration	O
.	O
</s>
<s>
Three	O
significant	O
versions	O
of	O
SNMP	B-Protocol
have	O
been	O
developed	O
and	O
deployed	O
.	O
</s>
<s>
SNMP	B-Protocol
is	O
a	O
component	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
as	O
defined	O
by	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
.	O
</s>
<s>
It	O
consists	O
of	O
a	O
set	O
of	O
standards	O
for	O
network	O
management	O
,	O
including	O
an	O
application	B-Application
layer	I-Application
protocol	O
,	O
a	O
database	O
schema	B-Application
,	O
and	O
a	O
set	O
of	O
data	O
objects	O
.	O
</s>
<s>
In	O
typical	O
uses	O
of	O
SNMP	B-Protocol
,	O
one	O
or	O
more	O
administrative	O
computers	O
called	O
managers	O
have	O
the	O
task	O
of	O
monitoring	O
or	O
managing	O
a	O
group	O
of	O
hosts	O
or	O
devices	O
on	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Each	O
managed	O
system	O
executes	O
a	O
software	O
component	O
called	O
an	O
agent	B-General_Concept
which	O
reports	O
information	O
via	O
SNMP	B-Protocol
to	O
the	O
manager	O
.	O
</s>
<s>
An	O
SNMP-managed	O
network	O
consists	O
of	O
three	O
key	O
components	O
:	O
</s>
<s>
A	O
managed	O
device	O
is	O
a	O
network	O
node	O
that	O
implements	O
an	O
SNMP	B-Protocol
interface	O
that	O
allows	O
unidirectional	O
(	O
read-only	O
)	O
or	O
bidirectional	O
(	O
read	O
and	O
write	O
)	O
access	O
to	O
node-specific	O
information	O
.	O
</s>
<s>
Sometimes	O
called	O
network	O
elements	O
,	O
the	O
managed	O
devices	O
can	O
be	O
any	O
type	O
of	O
device	O
,	O
including	O
,	O
but	O
not	O
limited	O
to	O
,	O
routers	B-Protocol
,	O
access	O
servers	O
,	O
switches	B-Protocol
,	O
cable	B-Device
modems	I-Device
,	O
bridges	O
,	O
hubs	B-Protocol
,	O
IP	B-Device
telephones	I-Device
,	O
IP	B-Algorithm
video	I-Algorithm
cameras	I-Algorithm
,	O
computer	O
hosts	O
,	O
and	O
printers	O
.	O
</s>
<s>
An	O
agent	B-General_Concept
is	O
a	O
network-management	O
software	O
module	O
that	O
resides	O
on	O
a	O
managed	O
device	O
.	O
</s>
<s>
An	O
agent	B-General_Concept
has	O
local	O
knowledge	O
of	O
management	O
information	O
and	O
translates	O
that	O
information	O
to	O
or	O
from	O
an	O
SNMP-specific	O
form	O
.	O
</s>
<s>
SNMP	B-Protocol
agents	O
expose	O
management	O
data	O
on	O
the	O
managed	O
systems	O
as	O
variables	O
.	O
</s>
<s>
The	O
variables	O
accessible	O
via	O
SNMP	B-Protocol
are	O
organized	O
in	O
hierarchies	O
.	O
</s>
<s>
SNMP	B-Protocol
itself	O
does	O
not	O
define	O
which	O
variables	O
a	O
managed	O
system	O
should	O
offer	O
.	O
</s>
<s>
Rather	O
,	O
SNMP	B-Protocol
uses	O
an	O
extensible	O
design	O
that	O
allows	O
applications	O
to	O
define	O
their	O
own	O
hierarchies	O
.	O
</s>
<s>
Each	O
OID	O
identifies	O
a	O
variable	O
that	O
can	O
be	O
read	O
or	O
set	O
via	O
SNMP	B-Protocol
.	O
</s>
<s>
MIBs	O
use	O
the	O
notation	O
defined	O
by	O
Structure	B-Application
of	I-Application
Management	I-Application
Information	I-Application
Version	O
2.0	O
(	O
SMIv2	O
,	O
)	O
,	O
a	O
subset	O
of	O
ASN.1	B-Protocol
.	O
</s>
<s>
SNMP	B-Protocol
operates	O
in	O
the	O
application	B-Application
layer	I-Application
of	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
All	O
SNMP	B-Protocol
messages	O
are	O
transported	O
via	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
The	O
SNMP	B-Protocol
agent	B-General_Concept
receives	O
requests	O
on	O
UDP	B-Protocol
port	I-Protocol
161	O
.	O
</s>
<s>
The	O
manager	O
may	O
send	O
requests	O
from	O
any	O
available	O
source	O
port	O
to	O
port	O
161	O
in	O
the	O
agent	B-General_Concept
.	O
</s>
<s>
The	O
agent	B-General_Concept
response	O
is	O
sent	O
back	O
to	O
the	O
source	O
port	O
on	O
the	O
manager	O
.	O
</s>
<s>
The	O
manager	O
receives	O
notifications	O
(	O
Traps	B-Application
and	O
InformRequests	O
)	O
on	O
port	O
162	O
.	O
</s>
<s>
The	O
agent	B-General_Concept
may	O
generate	O
notifications	O
from	O
any	O
available	O
port	O
.	O
</s>
<s>
When	O
used	O
with	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
or	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
,	O
requests	O
are	O
received	O
on	O
port	O
10161	O
and	O
notifications	O
are	O
sent	O
to	O
port	O
10162	O
.	O
</s>
<s>
SNMPv1	O
specifies	O
five	O
core	O
protocol	B-Protocol
data	I-Protocol
units	I-Protocol
(	O
PDUs	O
)	O
.	O
</s>
<s>
All	O
SNMP	B-Protocol
PDUs	O
are	O
constructed	O
as	O
follows	O
:	O
</s>
<s>
The	O
seven	O
SNMP	B-Protocol
PDU	O
types	O
as	O
identified	O
by	O
the	O
PDU-type	O
field	O
are	O
as	O
follows	O
:	O
</s>
<s>
GetRequest	O
A	O
manager-to-agent	O
request	O
to	O
retrieve	O
the	O
value	O
of	O
a	O
variable	O
or	O
list	O
of	O
variables	O
.	O
</s>
<s>
Retrieval	O
of	O
the	O
specified	O
variable	O
values	O
is	O
to	O
be	O
done	O
as	O
an	O
atomic	B-General_Concept
operation	I-General_Concept
by	O
the	O
agent	B-General_Concept
.	O
</s>
<s>
SetRequest	O
A	O
manager-to-agent	O
request	O
to	O
change	O
the	O
value	O
of	O
a	O
variable	O
or	O
list	O
of	O
variables	O
.	O
</s>
<s>
Changes	O
to	O
all	O
specified	O
variables	O
are	O
to	O
be	O
made	O
as	O
an	O
atomic	B-General_Concept
operation	I-General_Concept
by	O
the	O
agent	B-General_Concept
.	O
</s>
<s>
GetNextRequest	O
A	O
manager-to-agent	O
request	O
to	O
discover	O
available	O
variables	O
and	O
their	O
values	O
.	O
</s>
<s>
The	O
entire	O
MIB	O
of	O
an	O
agent	B-General_Concept
can	O
be	O
walked	O
by	O
iterative	O
application	B-Application
of	O
GetNextRequest	O
starting	O
at	O
OID	O
0	O
.	O
</s>
<s>
GetBulkRequest	O
A	O
manager-to-agent	O
request	O
for	O
multiple	O
iterations	O
of	O
GetNextRequest	O
.	O
</s>
<s>
Response	O
Returns	O
variable	O
bindings	O
and	O
acknowledgement	O
from	O
agent	B-General_Concept
to	O
manager	O
for	O
GetRequest	O
,	O
SetRequest	O
,	O
GetNextRequest	O
,	O
GetBulkRequest	O
and	O
InformRequest	O
.	O
</s>
<s>
Asynchronous	O
notification	O
from	O
agent	B-General_Concept
to	O
manager	O
.	O
</s>
<s>
While	O
in	O
other	O
SNMP	B-Protocol
communication	O
,	O
the	O
manager	O
actively	O
requests	O
information	O
from	O
the	O
agent	B-General_Concept
,	O
these	O
are	O
PDUs	O
that	O
are	O
sent	O
from	O
the	O
agent	B-General_Concept
to	O
the	O
manager	O
without	O
being	O
explicitly	O
requested	O
.	O
</s>
<s>
SNMP	B-Protocol
traps	B-Application
enable	O
an	O
agent	B-General_Concept
to	O
notify	O
the	O
management	O
station	O
of	O
significant	O
events	O
by	O
way	O
of	O
an	O
unsolicited	O
SNMP	B-Protocol
message	O
.	O
</s>
<s>
Trap	B-Application
PDUs	O
include	O
current	O
sysUpTime	O
value	O
,	O
an	O
OID	O
identifying	O
the	O
type	O
of	O
trap	B-Application
and	O
optional	O
variable	O
bindings	O
.	O
</s>
<s>
Destination	O
addressing	O
for	O
traps	B-Application
is	O
determined	O
in	O
an	O
application-specific	O
manner	O
typically	O
through	O
trap	B-Application
configuration	O
variables	O
in	O
the	O
MIB	O
.	O
</s>
<s>
The	O
format	O
of	O
the	O
trap	B-Application
message	O
was	O
changed	O
in	O
SNMPv2	O
and	O
the	O
PDU	O
was	O
renamed	O
SNMPv2-Trap	O
.	O
</s>
<s>
Later	O
implementations	O
have	O
loosened	O
the	O
original	O
definition	O
to	O
allow	O
agent	B-General_Concept
to	O
manager	O
communications	O
.	O
</s>
<s>
Manager-to-manager	O
notifications	O
were	O
already	O
possible	O
in	O
SNMPv1	O
using	O
a	O
Trap	B-Application
,	O
but	O
as	O
SNMP	B-Protocol
commonly	O
runs	O
over	O
UDP	O
where	O
delivery	O
is	O
not	O
assured	O
and	O
dropped	O
packets	O
are	O
not	O
reported	O
,	O
delivery	O
of	O
a	O
Trap	B-Application
was	O
not	O
guaranteed	O
.	O
</s>
<s>
specifies	O
that	O
an	O
SNMP	B-Protocol
implementation	O
must	O
accept	O
a	O
message	O
of	O
at	O
least	O
484	O
bytes	O
in	O
length	O
.	O
</s>
<s>
In	O
practice	O
,	O
SNMP	B-Protocol
implementations	O
accept	O
longer	O
messages	O
.	O
</s>
<s>
If	O
implemented	O
correctly	O
,	O
an	O
SNMP	B-Protocol
message	O
is	O
discarded	O
if	O
the	O
decoding	O
of	O
the	O
message	O
fails	O
and	O
thus	O
malformed	O
SNMP	B-Protocol
requests	O
are	O
ignored	O
.	O
</s>
<s>
A	O
successfully	O
decoded	O
SNMP	B-Protocol
request	O
is	O
then	O
authenticated	O
using	O
the	O
community	O
string	O
.	O
</s>
<s>
If	O
the	O
authentication	O
fails	O
,	O
a	O
trap	B-Application
is	O
generated	O
indicating	O
an	O
authentication	O
failure	O
and	O
the	O
message	O
is	O
dropped	O
.	O
</s>
<s>
Most	O
agents	O
support	O
three	O
community	O
names	O
,	O
one	O
each	O
for	O
read-only	O
,	O
read-write	O
and	O
trap	B-Application
.	O
</s>
<s>
The	O
trap	B-Application
community	O
string	O
applies	O
to	O
receipt	O
of	O
traps	B-Application
.	O
</s>
<s>
SNMPv3	O
also	O
uses	O
community	O
strings	O
,	O
but	O
allows	O
for	O
secure	O
authentication	O
and	O
communication	O
between	O
SNMP	B-Protocol
manager	O
and	O
agent	B-General_Concept
.	O
</s>
<s>
In	O
practice	O
,	O
SNMP	B-Protocol
implementations	O
often	O
support	O
multiple	O
versions	O
:	O
typically	O
SNMPv1	O
,	O
SNMPv2c	O
,	O
and	O
SNMPv3	O
.	O
</s>
<s>
SNMP	B-Protocol
version	O
1	O
(	O
SNMPv1	O
)	O
is	O
the	O
initial	O
implementation	O
of	O
the	O
SNMP	B-Protocol
protocol	O
.	O
</s>
<s>
SNMP	B-Protocol
was	O
approved	O
based	O
on	O
a	O
belief	O
that	O
it	O
was	O
an	O
interim	O
protocol	O
needed	O
for	O
taking	O
steps	O
towards	O
large-scale	O
deployment	O
of	O
the	O
Internet	O
and	O
its	O
commercialization	O
.	O
</s>
<s>
The	O
first	O
Request	O
for	O
Comments	O
(	O
RFCs	O
)	O
for	O
SNMP	B-Protocol
,	O
now	O
known	O
as	O
SNMPv1	O
,	O
appeared	O
in	O
1988	O
:	O
</s>
<s>
SNMPv1	O
may	O
be	O
carried	O
by	O
transport	B-Architecture
layer	I-Architecture
protocols	O
such	O
as	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
,	O
OSI	O
Connectionless-mode	B-Protocol
Network	I-Protocol
Service	I-Protocol
(	O
CLNS	B-Protocol
)	O
,	O
AppleTalk	O
Datagram	B-Protocol
Delivery	I-Protocol
Protocol	I-Protocol
(	O
DDP	O
)	O
,	O
and	O
Novell	O
Internetwork	B-Protocol
Packet	I-Protocol
Exchange	I-Protocol
(	O
IPX	B-Protocol
)	O
.	O
</s>
<s>
The	O
specification	O
does	O
,	O
in	O
fact	O
,	O
allow	O
room	O
for	O
custom	O
authentication	O
to	O
be	O
used	O
,	O
but	O
widely	O
used	O
implementations	O
"	O
support	O
only	O
a	O
trivial	O
authentication	O
service	O
that	O
identifies	O
all	O
SNMP	B-Protocol
messages	O
as	O
authentic	O
SNMP	B-Protocol
messages.	O
"	O
</s>
<s>
For	O
example	O
,	O
an	O
organization	O
may	O
consider	O
their	O
internal	O
network	O
to	O
be	O
sufficiently	O
secure	O
that	O
no	O
encryption	O
is	O
necessary	O
for	O
its	O
SNMP	B-Protocol
messages	O
.	O
</s>
<s>
This	O
version	O
of	O
SNMP	B-Protocol
reached	O
the	O
Proposed	O
Standard	O
level	O
of	O
maturity	O
,	O
but	O
was	O
deemed	O
obsolete	O
by	O
later	O
versions	O
.	O
</s>
<s>
Community-Based	O
Simple	B-Protocol
Network	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
version	O
2	O
,	O
or	O
SNMPv2c	O
,	O
is	O
defined	O
in	O
–	O
.	O
</s>
<s>
SNMPv2c	O
comprises	O
SNMPv2	O
without	O
the	O
controversial	O
new	O
SNMP	B-Protocol
v2	O
security	O
model	O
,	O
using	O
instead	O
the	O
simple	O
community-based	O
security	O
scheme	O
of	O
SNMPv1	O
.	O
</s>
<s>
User-Based	O
Simple	B-Protocol
Network	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
version	O
2	O
,	O
or	O
SNMPv2u	O
,	O
is	O
defined	O
in	O
–	O
.	O
</s>
<s>
A	O
variant	O
of	O
this	O
was	O
commercialized	O
as	O
SNMP	B-Protocol
v2*	O
,	O
and	O
the	O
mechanism	O
was	O
eventually	O
adopted	O
as	O
one	O
of	O
two	O
security	O
frameworks	O
in	O
SNMP	B-Protocol
v3	O
.	O
</s>
<s>
SNMP	B-Protocol
version	O
2	O
introduces	O
the	O
option	O
for	O
64-bit	O
data	O
counters	O
.	O
</s>
<s>
For	O
example	O
,	O
1.6	O
terabit	B-Protocol
Ethernet	I-Protocol
is	O
predicted	O
to	O
become	O
available	O
by	O
2025	O
.	O
</s>
<s>
SNMPv2c	O
messages	O
use	O
different	O
header	O
and	O
protocol	B-Protocol
data	I-Protocol
unit	I-Protocol
(	O
PDU	O
)	O
formats	O
than	O
SNMPv1	O
messages	O
.	O
</s>
<s>
An	O
SNMPv2	O
agent	B-General_Concept
can	O
act	O
as	O
a	O
proxy	O
agent	B-General_Concept
on	O
behalf	O
of	O
SNMPv1	O
managed	O
devices	O
.	O
</s>
<s>
When	O
an	O
SNMPv2	O
NMS	O
issues	O
a	O
command	O
intended	O
for	O
an	O
SNMPv1	O
agent	B-General_Concept
it	O
sends	O
it	O
to	O
the	O
SNMPv2	O
proxy	O
agent	B-General_Concept
instead	O
.	O
</s>
<s>
The	O
proxy	O
agent	B-General_Concept
forwards	O
Get	O
,	O
GetNext	O
,	O
and	O
Set	O
messages	O
to	O
the	O
SNMPv1	O
agent	B-General_Concept
unchanged	O
.	O
</s>
<s>
GetBulk	O
messages	O
are	O
converted	O
by	O
the	O
proxy	O
agent	B-General_Concept
to	O
GetNext	O
messages	O
and	O
then	O
are	O
forwarded	O
to	O
the	O
SNMPv1	O
agent	B-General_Concept
.	O
</s>
<s>
Additionally	O
,	O
the	O
proxy	O
agent	B-General_Concept
receives	O
and	O
maps	O
SNMPv1	O
trap	B-Application
messages	O
to	O
SNMPv2	O
trap	B-Application
messages	O
and	O
then	O
forwards	O
them	O
to	O
the	O
NMS	O
.	O
</s>
<s>
To	O
support	O
this	O
dual-management	O
environment	O
,	O
a	O
management	O
application	B-Application
examines	O
information	O
stored	O
in	O
a	O
local	O
database	O
to	O
determine	O
whether	O
the	O
agent	B-General_Concept
supports	O
SNMPv1	O
or	O
SNMPv2	O
.	O
</s>
<s>
Based	O
on	O
the	O
information	O
in	O
the	O
database	O
,	O
the	O
NMS	O
communicates	O
with	O
the	O
agent	B-General_Concept
using	O
the	O
appropriate	O
version	O
of	O
SNMP	B-Protocol
.	O
</s>
<s>
The	O
most	O
visible	O
change	O
was	O
to	O
define	O
a	O
secure	O
version	O
of	O
SNMP	B-Protocol
,	O
by	O
adding	O
security	O
and	O
remote	O
configuration	O
enhancements	O
to	O
SNMP	B-Protocol
.	O
</s>
<s>
The	O
changes	O
also	O
facilitate	O
remote	O
configuration	O
and	O
administration	O
of	O
the	O
SNMP	B-Protocol
entities	O
,	O
as	O
well	O
as	O
addressing	O
issues	O
related	O
to	O
the	O
large-scale	O
deployment	O
,	O
accounting	O
,	O
and	O
fault	O
management	O
.	O
</s>
<s>
Identification	O
of	O
SNMP	B-Protocol
entities	O
to	O
facilitate	O
communication	O
only	O
between	O
known	O
SNMP	B-Protocol
entities	O
–	O
Each	O
SNMP	B-Protocol
entity	O
has	O
an	O
identifier	O
called	O
the	O
SNMPEngineID	O
,	O
and	O
SNMP	B-Protocol
communication	O
is	O
possible	O
only	O
if	O
an	O
SNMP	B-Protocol
entity	O
knows	O
the	O
identity	O
of	O
its	O
peer	O
.	O
</s>
<s>
Traps	B-Application
and	O
Notifications	O
are	O
exceptions	O
to	O
this	O
rule	O
.	O
</s>
<s>
Modification	O
of	O
Information	O
–	O
Protection	O
against	O
some	O
unauthorized	O
SNMP	B-Protocol
entity	O
altering	O
in-transit	B-General_Concept
messages	I-General_Concept
generated	O
by	O
an	O
authorized	O
principal	O
.	O
</s>
<s>
Disclosure	O
–	O
Protection	O
against	O
eavesdropping	O
on	O
the	O
exchanges	O
between	O
SNMP	B-Protocol
engines	O
.	O
</s>
<s>
Definition	O
of	O
different	O
authentication	O
and	O
privacy	O
protocols	O
–	O
MD5	B-Algorithm
,	O
SHA	O
and	O
HMAC-SHA-2	O
authentication	B-Protocol
protocols	I-Protocol
and	O
the	O
CBC_DES	O
and	O
CFB_AES_128	O
privacy	O
protocols	O
are	O
supported	O
in	O
the	O
USM	O
.	O
</s>
<s>
Definition	O
of	O
a	O
discovery	O
procedure	O
–	O
To	O
find	O
the	O
SNMPEngineID	O
of	O
an	O
SNMP	B-Protocol
entity	O
for	O
a	O
given	O
transport	O
address	O
and	O
transport	O
endpoint	O
address	O
.	O
</s>
<s>
Definition	O
of	O
the	O
time	O
synchronization	O
procedure	O
–	O
To	O
facilitate	O
authenticated	O
communication	O
between	O
the	O
SNMP	B-Protocol
entities	O
.	O
</s>
<s>
Definition	O
of	O
the	O
SNMP	B-Protocol
framework	O
MIB	O
–	O
To	O
facilitate	O
remote	O
configuration	O
and	O
administration	O
of	O
the	O
SNMP	B-Protocol
entity	O
.	O
</s>
<s>
Security	O
was	O
one	O
of	O
the	O
biggest	O
weakness	O
of	O
SNMP	B-Protocol
until	O
v3	O
.	O
</s>
<s>
Authentication	O
in	O
SNMP	B-Protocol
Versions	O
1	O
and	O
2	O
amounts	O
to	O
nothing	O
more	O
than	O
a	O
password	O
(	O
community	O
string	O
)	O
sent	O
in	O
clear	O
text	O
between	O
a	O
manager	O
and	O
agent	B-General_Concept
.	O
</s>
<s>
v3	O
also	O
defines	O
the	O
USM	O
and	O
VACM	O
,	O
which	O
were	O
later	O
followed	O
by	O
a	O
transport	O
security	O
model	O
(	O
TSM	O
)	O
that	O
provided	O
support	O
for	O
SNMPv3	O
over	O
SSH	O
and	O
SNMPv3	O
over	O
TLS	O
and	O
DTLS	B-Protocol
.	O
</s>
<s>
Two	O
transports	O
,	O
SSH	O
and	O
TLS/DTLS	O
,	O
have	O
been	O
defined	O
that	O
make	O
use	O
of	O
the	O
TSM	O
specification	O
.	O
</s>
<s>
the	O
IETF	O
recognizes	O
Simple	B-Protocol
Network	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
version	O
3	O
as	O
defined	O
by	O
–	O
(	O
also	O
known	O
as	O
STD0062	O
)	O
as	O
the	O
current	O
standard	O
version	O
of	O
SNMP	B-Protocol
.	O
</s>
<s>
SNMP	B-Protocol
's	O
powerful	O
write	O
capabilities	O
,	O
which	O
would	O
allow	O
the	O
configuration	O
of	O
network	O
devices	O
,	O
are	O
not	O
being	O
fully	O
utilized	O
by	O
many	O
vendors	O
,	O
partly	O
because	O
of	O
a	O
lack	O
of	O
security	O
in	O
SNMP	B-Protocol
versions	O
before	O
SNMPv3	O
,	O
and	O
partly	O
because	O
many	O
devices	O
simply	O
are	O
not	O
capable	O
of	O
being	O
configured	O
via	O
individual	O
MIB	O
object	O
changes	O
.	O
</s>
<s>
Some	O
SNMP	B-Protocol
values	O
(	O
especially	O
tabular	O
values	O
)	O
require	O
specific	O
knowledge	O
of	O
table	O
indexing	O
schemes	O
,	O
and	O
these	O
index	O
values	O
are	O
not	O
necessarily	O
consistent	O
across	O
platforms	O
.	O
</s>
<s>
Some	O
major	O
equipment	O
vendors	O
tend	O
to	O
over-extend	O
their	O
proprietary	O
command	B-Application
line	I-Application
interface	I-Application
(	O
CLI	O
)	O
centric	O
configuration	O
and	O
control	O
systems	O
.	O
</s>
<s>
In	O
February	O
2002	O
the	O
Carnegie	O
Mellon	O
Software	O
Engineering	O
Institute	O
(	O
CM-SEI	O
)	O
Computer	O
Emergency	O
Response	O
Team	O
Coordination	O
Center	O
(	O
CERT-CC	O
)	O
issued	O
an	O
Advisory	O
on	O
SNMPv1	O
,	O
after	O
the	O
Oulu	O
University	O
Secure	O
Programming	O
Group	O
conducted	O
a	O
thorough	O
analysis	O
of	O
SNMP	B-Protocol
message	O
handling	O
.	O
</s>
<s>
Most	O
SNMP	B-Protocol
implementations	O
,	O
regardless	O
of	O
which	O
version	O
of	O
the	O
protocol	O
they	O
support	O
,	O
use	O
the	O
same	O
program	O
code	O
for	O
decoding	O
protocol	B-Protocol
data	I-Protocol
units	I-Protocol
(	O
PDU	O
)	O
and	O
problems	O
were	O
identified	O
in	O
this	O
code	O
.	O
</s>
<s>
Other	O
problems	O
were	O
found	O
with	O
decoding	O
SNMP	B-Protocol
trap	B-Application
messages	O
received	O
by	O
the	O
SNMP	B-Protocol
management	O
station	O
or	O
requests	O
received	O
by	O
the	O
SNMP	B-Protocol
agent	B-General_Concept
on	O
the	O
network	O
device	O
.	O
</s>
<s>
Many	O
vendors	O
had	O
to	O
issue	O
patches	O
for	O
their	O
SNMP	B-Protocol
implementations	O
.	O
</s>
<s>
Because	O
SNMP	B-Protocol
is	O
designed	O
to	O
allow	O
administrators	O
to	O
monitor	O
and	O
configure	O
network	O
devices	O
remotely	O
it	O
can	O
also	O
be	O
used	O
to	O
penetrate	O
a	O
network	O
.	O
</s>
<s>
A	O
significant	O
number	O
of	O
software	O
tools	O
can	O
scan	O
the	O
entire	O
network	O
using	O
SNMP	B-Protocol
,	O
therefore	O
mistakes	O
in	O
the	O
configuration	O
of	O
the	O
read-write	O
mode	O
can	O
make	O
a	O
network	O
susceptible	O
to	O
attacks	O
.	O
</s>
<s>
In	O
2001	O
,	O
Cisco	O
released	O
information	O
that	O
indicated	O
that	O
,	O
even	O
in	O
read-only	O
mode	O
,	O
the	O
SNMP	B-Protocol
implementation	O
of	O
Cisco	B-Protocol
IOS	I-Protocol
is	O
vulnerable	O
to	O
certain	O
denial	O
of	O
service	O
attacks	O
.	O
</s>
<s>
These	O
security	O
issues	O
can	O
be	O
fixed	O
through	O
an	O
IOS	B-Protocol
upgrade	O
.	O
</s>
<s>
If	O
SNMP	B-Protocol
is	O
not	O
used	O
in	O
a	O
network	O
it	O
should	O
be	O
disabled	O
in	O
network	O
devices	O
.	O
</s>
<s>
When	O
configuring	O
SNMP	B-Protocol
read-only	O
mode	O
,	O
close	O
attention	O
should	O
be	O
paid	O
to	O
the	O
configuration	O
of	O
the	O
access	O
control	O
and	O
from	O
which	O
IP	B-Protocol
addresses	O
SNMP	B-Protocol
messages	O
are	O
accepted	O
.	O
</s>
<s>
If	O
the	O
SNMP	B-Protocol
servers	O
are	O
identified	O
by	O
their	O
IP	B-Protocol
,	O
SNMP	B-Protocol
is	O
only	O
allowed	O
to	O
respond	O
to	O
these	O
IPs	O
and	O
SNMP	B-Protocol
messages	O
from	O
other	O
IP	B-Protocol
addresses	O
would	O
be	O
denied	O
.	O
</s>
<s>
However	O
,	O
IP	B-Protocol
address	O
spoofing	O
remains	O
a	O
security	O
concern	O
.	O
</s>
<s>
SNMP	B-Protocol
is	O
available	O
in	O
different	O
versions	O
,	O
each	O
has	O
its	O
own	O
security	O
issues	O
.	O
</s>
<s>
SNMP	B-Protocol
v1	O
sends	O
passwords	O
in	O
clear-text	O
over	O
the	O
network	O
.	O
</s>
<s>
Therefore	O
,	O
passwords	O
can	O
be	O
read	O
with	O
packet	B-Protocol
sniffing	I-Protocol
.	O
</s>
<s>
SNMP	B-Protocol
v2	O
allows	O
password	O
hashing	O
with	O
MD5	B-Algorithm
,	O
but	O
this	O
has	O
to	O
be	O
configured	O
.	O
</s>
<s>
Virtually	O
all	O
network	O
management	O
software	O
support	O
SNMP	B-Protocol
v1	O
,	O
but	O
not	O
necessarily	O
SNMP	B-Protocol
v2	O
or	O
v3	O
.	O
</s>
<s>
SNMP	B-Protocol
v2	O
was	O
specifically	O
developed	O
to	O
provide	O
data	B-General_Concept
security	I-General_Concept
,	O
that	O
is	O
authentication	O
,	O
privacy	O
and	O
authorization	O
,	O
but	O
only	O
SNMP	B-Protocol
version	O
2c	O
gained	O
the	O
endorsement	O
of	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
,	O
while	O
versions	O
2u	O
and	O
2*	O
failed	O
to	O
gain	O
IETF	O
approval	O
due	O
to	O
security	O
issues	O
.	O
</s>
<s>
SNMP	B-Protocol
v3	O
uses	O
MD5	B-Algorithm
,	O
Secure	O
Hash	B-Algorithm
Algorithm	O
(	O
SHA	O
)	O
and	O
keyed	O
algorithms	O
to	O
offer	O
protection	O
against	O
unauthorized	O
data	O
modification	O
and	O
spoofing	O
attacks	O
.	O
</s>
<s>
If	O
a	O
higher	O
level	O
of	O
security	O
is	O
needed	O
the	O
Data	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
DES	B-Algorithm
)	O
can	O
be	O
optionally	O
used	O
in	O
the	O
cipher	O
block	O
chaining	O
mode	O
.	O
</s>
<s>
SNMP	B-Protocol
v3	O
is	O
implemented	O
on	O
Cisco	B-Protocol
IOS	I-Protocol
since	O
release	O
12.0(3 )	O
T	O
.	O
</s>
<s>
The	O
risk	O
of	O
guessing	O
authentication	O
strings	O
from	O
hash	B-Algorithm
values	O
transmitted	O
over	O
the	O
network	O
depends	O
on	O
the	O
cryptographic	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
used	O
and	O
the	O
length	O
of	O
the	O
hash	B-Algorithm
value	O
.	O
</s>
<s>
SNMPv3	O
uses	O
the	O
HMAC-SHA-2	O
authentication	B-Protocol
protocol	I-Protocol
for	O
the	O
User-based	O
Security	O
Model	O
(	O
USM	O
)	O
.	O
</s>
<s>
SNMP	B-Protocol
does	O
not	O
use	O
a	O
more	O
secure	O
challenge-handshake	B-Protocol
authentication	I-Protocol
protocol	I-Protocol
.	O
</s>
<s>
SNMPv3	O
(	O
like	O
other	O
SNMP	B-Protocol
protocol	O
versions	O
)	O
is	O
a	O
stateless	B-Protocol
protocol	I-Protocol
,	O
and	O
it	O
has	O
been	O
designed	O
with	O
a	O
minimal	O
amount	O
of	O
interactions	O
between	O
the	O
agent	B-General_Concept
and	O
the	O
manager	O
.	O
</s>
<s>
Thus	O
introducing	O
a	O
challenge-response	O
handshake	O
for	O
each	O
command	O
would	O
impose	O
a	O
burden	O
on	O
the	O
agent	B-General_Concept
(	O
and	O
possibly	O
on	O
the	O
network	O
itself	O
)	O
that	O
the	O
protocol	O
designers	O
deemed	O
excessive	O
and	O
unacceptable	O
.	O
</s>
<s>
The	O
security	O
deficiencies	O
of	O
all	O
SNMP	B-Protocol
versions	O
can	O
be	O
mitigated	O
by	O
IPsec	B-Protocol
authentication	O
and	O
confidentiality	O
mechanisms	O
.	O
</s>
<s>
SNMP	B-Protocol
also	O
may	O
be	O
carried	O
securely	O
over	O
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
.	O
</s>
<s>
Many	O
SNMP	B-Protocol
implementations	O
include	O
a	O
type	O
of	O
automatic	O
discovery	O
where	O
a	O
new	O
network	O
component	O
,	O
such	O
as	O
a	O
switch	O
or	O
router	B-Protocol
,	O
is	O
discovered	O
and	O
polled	O
automatically	O
.	O
</s>
<s>
To	O
alert	O
administrators	O
of	O
other	O
attempts	O
to	O
glean	O
community	O
strings	O
,	O
SNMP	B-Protocol
can	O
be	O
configured	O
to	O
pass	O
community-name	O
authentication	O
failure	O
traps	B-Application
.	O
</s>
<s>
If	O
SNMPv2	O
is	O
used	O
,	O
the	O
issue	O
can	O
be	O
avoided	O
by	O
enabling	O
password	O
encryption	O
on	O
the	O
SNMP	B-Protocol
agents	O
of	O
network	O
devices	O
.	O
</s>
<s>
Because	O
of	O
the	O
well-known	O
defaults	O
,	O
SNMP	B-Protocol
topped	O
the	O
list	O
of	O
the	O
SANS	O
Institute	O
's	O
Common	O
Default	O
Configuration	O
Issues	O
and	O
was	O
number	O
ten	O
on	O
the	O
SANS	O
Top	O
10	O
Most	O
Critical	O
Internet	O
Security	O
Threats	O
for	O
the	O
year	O
2000	O
.	O
</s>
<s>
Whether	O
it	O
runs	O
over	O
TCP	O
or	O
UDP	O
,	O
SNMPv1	O
and	O
v2	O
are	O
vulnerable	O
to	O
IP	B-Protocol
spoofing	O
attacks	O
.	O
</s>
<s>
With	O
spoofing	O
,	O
attackers	O
may	O
bypass	O
device	O
access	O
lists	O
in	O
agents	O
that	O
are	O
implemented	O
to	O
restrict	O
SNMP	B-Protocol
access	O
.	O
</s>
<s>
(	O
Proposed	O
)	O
—	O
Remote	O
Authentication	O
Dial-In	O
User	O
Service	O
(	O
RADIUS	O
)	O
Usage	O
for	O
Simple	B-Protocol
Network	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
(	O
SNMP	B-Protocol
)	O
Transport	O
Models	O
.	O
</s>
