Network Working Group Editor of this version:
Request for Comments: 3416 R. Presuhn
STD: 62 BMC Software, Inc.
Obsoletes: 1905 Authors of previous version:
Category: Standards Track J. Case
SNMP Research, Inc.
K. McCloghrie
Cisco Systems, Inc.
M. Rose
Dover Beach Consulting, Inc.
S. Waldbusser
International Network Services
December 2002
Version 2 of the Protocol Operations for
the Simple Network Management Protocol (SNMP)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document defines version 2 of the protocol operations for the
Simple Network Management Protocol (SNMP). It defines the syntax and
elements of procedure for sending, receiving, and processing SNMP
PDUs. This document obsoletes RFC 1905.
Presuhn, et al. Standards Track [Page 1]
RFC 3416 Protocol Operations for SNMP December 2002
Table of Contents
1. Introduction ................................................ 32. Overview .................................................... 42.1. Management Information .................................... 42.2. Retransmission of Requests ................................ 42.3. Message Sizes ............................................. 42.4. Transport Mappings ........................................ 52.5. SMIv2 Data Type Mappings .................................. 63. Definitions ................................................. 64. Protocol Specification ...................................... 94.1. Common Constructs ......................................... 94.2. PDU Processing ............................................ 104.2.1. The GetRequest-PDU ...................................... 104.2.2. The GetNextRequest-PDU .................................. 114.2.2.1. Example of Table Traversal ............................ 124.2.3. The GetBulkRequest-PDU .................................. 144.2.3.1. Another Example of Table Traversal .................... 174.2.4. The Response-PDU ........................................ 184.2.5. The SetRequest-PDU ...................................... 194.2.6. The SNMPv2-Trap-PDU ..................................... 224.2.7. The InformRequest-PDU ................................... 235. Notice on Intellectual Property ............................. 246. Acknowledgments ............................................. 247. Security Considerations ..................................... 268. References .................................................. 268.1. Normative References ...................................... 268.2. Informative References .................................... 279. Changes from RFC 1905 ....................................... 2810. Editor's Address ........................................... 3011. Full Copyright Statement ................................... 31
Presuhn, et al. Standards Track [Page 2]
RFC 3416 Protocol Operations for SNMP December 2002
The SNMP Management Framework at the time of this writing consists of
five major components:
- An overall architecture, described in STD 62, RFC 3411
[RFC3411].
- Mechanisms for describing and naming objects and events for the
purpose of management. The first version of this Structure of
Management Information (SMI) is called SMIv1 and described in
STD 16, RFC 1155 [RFC1155], STD 16, RFC 1212 [RFC1212] and RFC
1215 [RFC1215]. The second version, called SMIv2, is described
in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and
STD 58, RFC 2580 [RFC2580].
- Message protocols for transferring management information. The
first version of the SNMP message protocol is called SNMPv1 and
described in STD 15, RFC 1157 [RFC1157]. A second version of
the SNMP message protocol, which is not an Internet standards
track protocol, is called SNMPv2c and described in RFC 1901
[RFC1901] and STD 62, RFC 3417 [RFC3417]. The third version of
the message protocol is called SNMPv3 and described in STD 62,
RFC 3417 [RFC3417], RFC 3412 [RFC3412] and RFC 3414 [RFC3414].
- Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats is
described in STD 15, RFC 1157 [RFC1157]. A second set of
protocol operations and associated PDU formats is described in
this document.
- A set of fundamental applications described in STD 62, RFC 3413
[RFC3413] and the view-based access control mechanism described
in STD 62, RFC 3415 [RFC3415].
A more detailed introduction to the SNMP Management Framework at the
time of this writing can be found in RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. Objects in the MIB are
defined using the mechanisms defined in the SMI.
This document, Version 2 of the Protocol Operations for the Simple
Network Management Protocol, defines the operations of the protocol
with respect to the sending and receiving of PDUs to be carried by
the message protocol.
Presuhn, et al. Standards Track [Page 3]
RFC 3416 Protocol Operations for SNMP December 2002
SNMP entities supporting command generator or notification receiver
applications (traditionally called "managers") communicate with SNMP
entities supporting command responder or notification originator
applications (traditionally called "agents"). The purpose of this
protocol is the transport of management information and operations.
The term "variable" refers to an instance of a non-aggregate object
type defined according to the conventions set forth in the SMI
[RFC2578] or the textual conventions based on the SMI [RFC2579]. The
term "variable binding" normally refers to the pairing of the name of
a variable and its associated value. However, if certain kinds of
exceptional conditions occur during processing of a retrieval
request, a variable binding will pair a name and an indication of
that exception.
A variable-binding list is a simple list of variable bindings.
The name of a variable is an OBJECT IDENTIFIER which is the
concatenation of the OBJECT IDENTIFIER of the corresponding object-
type together with an OBJECT IDENTIFIER fragment identifying the
instance. The OBJECT IDENTIFIER of the corresponding object-type is
called the OBJECT IDENTIFIER prefix of the variable.
For all types of request in this protocol, the receiver is required
under normal circumstances, to generate and transmit a response to
the originator of the request. Whether or not a request should be
retransmitted if no corresponding response is received in an
appropriate time interval, is at the discretion of the application
originating the request. This will normally depend on the urgency of
the request. However, such an application needs to act responsibly
in respect to the frequency and duration of re-transmissions. See
BCP 41 [RFC2914] for discussion of relevant congestion control
principles.
The maximum size of an SNMP message is limited to the minimum of:
(1) the maximum message size which the destination SNMP entity can
accept; and,
Presuhn, et al. Standards Track [Page 4]
RFC 3416 Protocol Operations for SNMP December 2002
(2) the maximum message size which the source SNMP entity can
generate.
The former may be known on a per-recipient basis; and in the absence
of such knowledge, is indicated by transport domain used when sending
the message. The latter is imposed by implementation-specific local
constraints.
Each transport mapping for the SNMP indicates the minimum message
size which a SNMP implementation must be able to produce or consume.
Although implementations are encouraged to support larger values
whenever possible, a conformant implementation must never generate
messages larger than allowed by the receiving SNMP entity.
One of the aims of the GetBulkRequest-PDU, specified in this
protocol, is to minimize the number of protocol exchanges required to
retrieve a large amount of management information. As such, this PDU
type allows an SNMP entity supporting command generator applications
to request that the response be as large as possible given the
constraints on message sizes. These constraints include the limits
on the size of messages which the SNMP entity supporting command
responder applications can generate, and the SNMP entity supporting
command generator applications can receive.
However, it is possible that such maximum sized messages may be
larger than the Path MTU of the path across the network traversed by
the messages. In this situation, such messages are subject to
fragmentation. Fragmentation is generally considered to be harmful
[FRAG], since among other problems, it leads to a decrease in the
reliability of the transfer of the messages. Thus, an SNMP entity
which sends a GetBulkRequest-PDU must take care to set its parameters
accordingly, so as to reduce the risk of fragmentation. In
particular, under conditions of network stress, only small values
should be used for max-repetitions.
It is important to note that the exchange of SNMP messages requires
only an unreliable datagram service, with every message being
entirely and independently contained in a single transport datagram.
Specific transport mappings and encoding rules are specified
elsewhere [RFC3417]. However, the preferred mapping is the use of
the User Datagram Protocol [RFC768].
Presuhn, et al. Standards Track [Page 5]
RFC 3416 Protocol Operations for SNMP December 2002
The SMIv2 [RFC2578] defines 11 base types (INTEGER, OCTET STRING,
OBJECT IDENTIFIER, Integer32, IpAddress, Counter32, Gauge32,
Unsigned32, TimeTicks, Opaque, Counter64) and the BITS construct.
The SMIv2 base types are mapped to the corresponding selection type
in the SimpleSyntax and ApplicationSyntax choices of the ASN.1 SNMP
protocol definition. Note that the INTEGER and Integer32 SMIv2 base
types are mapped to the integer-value selection type of the
SimpleSyntax choice. Similarly, the Gauge32 and Unsigned32 SMIv2
base types are mapped to the unsigned-integer-value selection type of
the ApplicationSyntax choice.
The SMIv2 BITS construct is mapped to the string-value selection type
of the SimpleSyntax choice. A BITS value is encoded as an OCTET
STRING, in which all the named bits in (the definition of) the
bitstring, commencing with the first bit and proceeding to the last
bit, are placed in bits 8 (high order bit) to 1 (low order bit) of
the first octet, followed by bits 8 to 1 of each subsequent octet in
turn, followed by as many bits as are needed of the final subsequent
octet, commencing with bit 8. Remaining bits, if any, of the final
octet are set to zero on generation and ignored on receipt.
The value of the request-id field in a Response-PDU takes the value
of the request-id field in the request PDU to which it is a response.
By use of the request-id value, an application can distinguish the
(potentially multiple) outstanding requests, and thereby correlate
incoming responses with outstanding requests. In cases where an
unreliable datagram service is used, the request-id also provides a
simple means of identifying messages duplicated by the network. Use
of the same request-id on a retransmission of a request allows the
response to either the original transmission or the retransmission to
satisfy the request. However, in order to calculate the round trip
time for transmission and processing of a request-response
transaction, the application needs to use a different request-id
value on a retransmitted request. The latter strategy is recommended
for use in the majority of situations.
A non-zero value of the error-status field in a Response-PDU is used
to indicate that an error occurred to prevent the processing of the
request. In these cases, a non-zero value of the Response-PDU's
error-index field provides additional information by identifying
which variable binding in the list caused the error. A variable
binding is identified by its index value. The first variable binding
in a variable-binding list is index one, the second is index two,
etc.
Presuhn, et al. Standards Track [Page 9]
RFC 3416 Protocol Operations for SNMP December 2002
SNMP limits OBJECT IDENTIFIER values to a maximum of 128 sub-
identifiers, where each sub-identifier has a maximum value of
2**32-1.
In the elements of procedure below, any field of a PDU which is not
referenced by the relevant procedure is ignored by the receiving SNMP
entity. However, all components of a PDU, including those whose
values are ignored by the receiving SNMP entity, must have valid
ASN.1 syntax and encoding. For example, some PDUs (e.g., the
GetRequest-PDU) are concerned only with the name of a variable and
not its value. In this case, the value portion of the variable
binding is ignored by the receiving SNMP entity. The unSpecified
value is defined for use as the value portion of such bindings.
On generating a management communication, the message "wrapper" to
encapsulate the PDU is generated according to the "Elements of
Procedure" of the administrative framework in use. The definition of
"max-bindings" imposes an upper bound on the number of variable
bindings. In practice, the size of a message is also limited by
constraints on the maximum message size. A compliant implementation
must support as many variable bindings in a PDU or BulkPDU as fit
into the overall maximum message size limit of the SNMP engine, but
no more than 2147483647 variable bindings.
On receiving a management communication, the "Elements of Procedure"
of the administrative framework in use is followed, and if those
procedures indicate that the operation contained within the message
is to be performed locally, then those procedures also indicate the
MIB view which is visible to the operation.
A GetRequest-PDU is generated and transmitted at the request of an
application.
Upon receipt of a GetRequest-PDU, the receiving SNMP entity processes
each variable binding in the variable-binding list to produce a
Response-PDU. All fields of the Response-PDU have the same values as
the corresponding fields of the received request except as indicated
below. Each variable binding is processed as follows:
(1) If the variable binding's name exactly matches the name of a
variable accessible by this request, then the variable
binding's value field is set to the value of the named
variable.
Presuhn, et al. Standards Track [Page 10]
RFC 3416 Protocol Operations for SNMP December 2002
(2) Otherwise, if the variable binding's name does not have an
OBJECT IDENTIFIER prefix which exactly matches the OBJECT
IDENTIFIER prefix of any (potential) variable accessible by
this request, then its value field is set to "noSuchObject".
(3) Otherwise, the variable binding's value field is set to
"noSuchInstance".
If the processing of any variable binding fails for a reason other
than listed above, then the Response-PDU is re-formatted with the
same values in its request-id and variable-bindings fields as the
received GetRequest-PDU, with the value of its error-status field set
to "genErr", and the value of its error-index field is set to the
index of the failed variable binding.
Otherwise, the value of the Response-PDU's error-status field is set
to "noError", and the value of its error-index field is zero.
The generated Response-PDU is then encapsulated into a message. If
the size of the resultant message is less than or equal to both a
local constraint and the maximum message size of the originator, it
is transmitted to the originator of the GetRequest-PDU.
Otherwise, an alternate Response-PDU is generated. This alternate
Response-PDU is formatted with the same value in its request-id field
as the received GetRequest-PDU, with the value of its error-status
field set to "tooBig", the value of its error-index field set to
zero, and an empty variable-bindings field. This alternate
Response-PDU is then encapsulated into a message. If the size of the
resultant message is less than or equal to both a local constraint
and the maximum message size of the originator, it is transmitted to
the originator of the GetRequest-PDU. Otherwise, the snmpSilentDrops
[RFC3418] counter is incremented and the resultant message is
discarded.
A GetNextRequest-PDU is generated and transmitted at the request of
an application.
Upon receipt of a GetNextRequest-PDU, the receiving SNMP entity
processes each variable binding in the variable-binding list to
produce a Response-PDU. All fields of the Response-PDU have the same
values as the corresponding fields of the received request except as
indicated below. Each variable binding is processed as follows:
(1) The variable is located which is in the lexicographically
ordered list of the names of all variables which are
Presuhn, et al. Standards Track [Page 11]
RFC 3416 Protocol Operations for SNMP December 2002
accessible by this request and whose name is the first
lexicographic successor of the variable binding's name in
the incoming GetNextRequest-PDU. The corresponding variable
binding's name and value fields in the Response-PDU are set
to the name and value of the located variable.
(2) If the requested variable binding's name does not
lexicographically precede the name of any variable
accessible by this request, i.e., there is no lexicographic
successor, then the corresponding variable binding produced
in the Response-PDU has its value field set to
"endOfMibView", and its name field set to the variable
binding's name in the request.
If the processing of any variable binding fails for a reason other
than listed above, then the Response-PDU is re-formatted with the
same values in its request-id and variable-bindings fields as the
received GetNextRequest-PDU, with the value of its error-status field
set to "genErr", and the value of its error-index field is set to the
index of the failed variable binding.
Otherwise, the value of the Response-PDU's error-status field is set
to "noError", and the value of its error-index field is zero.
The generated Response-PDU is then encapsulated into a message. If
the size of the resultant message is less than or equal to both a
local constraint and the maximum message size of the originator, it
is transmitted to the originator of the GetNextRequest-PDU.
Otherwise, an alternate Response-PDU is generated. This alternate
Response-PDU is formatted with the same values in its request-id
field as the received GetNextRequest-PDU, with the value of its
error-status field set to "tooBig", the value of its error-index
field set to zero, and an empty variable-bindings field. This
alternate Response-PDU is then encapsulated into a message. If the
size of the resultant message is less than or equal to both a local
constraint and the maximum message size of the originator, it is
transmitted to the originator of the GetNextRequest-PDU. Otherwise,
the snmpSilentDrops [RFC3418] counter is incremented and the
resultant message is discarded.
An important use of the GetNextRequest-PDU is the traversal of
conceptual tables of information within a MIB. The semantics of this
type of request, together with the method of identifying individual
instances of objects in the MIB, provides access to related objects
in the MIB as if they enjoyed a tabular organization.
Presuhn, et al. Standards Track [Page 12]
RFC 3416 Protocol Operations for SNMP December 2002
In the protocol exchange sketched below, an application retrieves the
media-dependent physical address and the address-mapping type for
each entry in the IP net-to-media Address Translation Table [RFC1213]
of a particular network element. It also retrieves the value of
sysUpTime [RFC3418], at which the mappings existed. Suppose that the
command responder's IP net-to-media table has three entries:
Interface-Number Network-Address Physical-Address Type
1 10.0.0.51 00:00:10:01:23:45 static
1 9.2.3.4 00:00:10:54:32:10 dynamic
2 10.0.0.15 00:00:10:98:76:54 dynamic
The SNMP entity supporting a command generator application begins by
sending a GetNextRequest-PDU containing the indicated OBJECT
IDENTIFIER values as the requested variable names:
GetNextRequest ( sysUpTime,
ipNetToMediaPhysAddress,
ipNetToMediaType )
The SNMP entity supporting a command responder application responds
with a Response-PDU:
Response (( sysUpTime.0 = "123456" ),
( ipNetToMediaPhysAddress.1.9.2.3.4 = "000010543210" ),
( ipNetToMediaType.1.9.2.3.4 = "dynamic" ))
The SNMP entity supporting the command generator application
continues with:
GetNextRequest ( sysUpTime,
ipNetToMediaPhysAddress.1.9.2.3.4,
ipNetToMediaType.1.9.2.3.4 )
The SNMP entity supporting the command responder application responds
with:
Response (( sysUpTime.0 = "123461" ),
( ipNetToMediaPhysAddress.1.10.0.0.51 = "000010012345" ),
( ipNetToMediaType.1.10.0.0.51 = "static" ))
The SNMP entity supporting the command generator application
continues with:
GetNextRequest ( sysUpTime,
ipNetToMediaPhysAddress.1.10.0.0.51,
ipNetToMediaType.1.10.0.0.51 )
Presuhn, et al. Standards Track [Page 13]
RFC 3416 Protocol Operations for SNMP December 2002
The SNMP entity supporting the command responder application responds
with:
Response (( sysUpTime.0 = "123466" ),
( ipNetToMediaPhysAddress.2.10.0.0.15 = "000010987654" ),
( ipNetToMediaType.2.10.0.0.15 = "dynamic" ))
The SNMP entity supporting the command generator application
continues with:
GetNextRequest ( sysUpTime,
ipNetToMediaPhysAddress.2.10.0.0.15,
ipNetToMediaType.2.10.0.0.15 )
As there are no further entries in the table, the SNMP entity
supporting the command responder application responds with the
variables that are next in the lexicographical ordering of the
accessible object names, for example:
Response (( sysUpTime.0 = "123471" ),
( ipNetToMediaNetAddress.1.9.2.3.4 = "9.2.3.4" ),
( ipRoutingDiscards.0 = "2" ))
Note how, having reached the end of the column for
ipNetToMediaPhysAddress, the second variable binding from the command
responder application has now "wrapped" to the first row in the next
column. Furthermore, note how, having reached the end of the
ipNetToMediaTable for the third variable binding, the command
responder application has responded with the next available object,
which is outside that table. This response signals the end of the
table to the command generator application.
A GetBulkRequest-PDU is generated and transmitted at the request of
an application. The purpose of the GetBulkRequest-PDU is to request
the transfer of a potentially large amount of data, including, but
not limited to, the efficient and rapid retrieval of large tables.
Upon receipt of a GetBulkRequest-PDU, the receiving SNMP entity
processes each variable binding in the variable-binding list to
produce a Response-PDU with its request-id field having the same
value as in the request.
For the GetBulkRequest-PDU type, the successful processing of each
variable binding in the request generates zero or more variable
bindings in the Response-PDU. That is, the one-to-one mapping
between the variable bindings of the GetRequest-PDU, GetNextRequest-
Presuhn, et al. Standards Track [Page 14]
RFC 3416 Protocol Operations for SNMP December 2002
PDU, and SetRequest-PDU types and the resultant Response-PDUs does
not apply for the mapping between the variable bindings of a
GetBulkRequest-PDU and the resultant Response-PDU.
The values of the non-repeaters and max-repetitions fields in the
request specify the processing requested. One variable binding in
the Response-PDU is requested for the first N variable bindings in
the request and M variable bindings are requested for each of the R
remaining variable bindings in the request. Consequently, the total
number of requested variable bindings communicated by the request is
given by N + (M * R), where N is the minimum of: a) the value of the
non-repeaters field in the request, and b) the number of variable
bindings in the request; M is the value of the max-repetitions field
in the request; and R is the maximum of: a) number of variable
bindings in the request - N, and b) zero.
The receiving SNMP entity produces a Response-PDU with up to the
total number of requested variable bindings communicated by the
request. The request-id shall have the same value as the received
GetBulkRequest-PDU.
If N is greater than zero, the first through the (N)-th variable
bindings of the Response-PDU are each produced as follows:
(1) The variable is located which is in the lexicographically
ordered list of the names of all variables which are accessible
by this request and whose name is the first lexicographic
successor of the variable binding's name in the incoming
GetBulkRequest-PDU. The corresponding variable binding's name
and value fields in the Response-PDU are set to the name and
value of the located variable.
(2) If the requested variable binding's name does not
lexicographically precede the name of any variable accessible
by this request, i.e., there is no lexicographic successor,
then the corresponding variable binding produced in the
Response-PDU has its value field set to "endOfMibView", and its
name field set to the variable binding's name in the request.
If M and R are non-zero, the (N + 1)-th and subsequent variable
bindings of the Response-PDU are each produced in a similar manner.
For each iteration i, such that i is greater than zero and less than
or equal to M, and for each repeated variable, r, such that r is
greater than zero and less than or equal to R, the (N + ( (i-1) * R )
+ r)-th variable binding of the Response-PDU is produced as follows:
Presuhn, et al. Standards Track [Page 15]
RFC 3416 Protocol Operations for SNMP December 2002
(1) The variable which is in the lexicographically ordered list of
the names of all variables which are accessible by this request
and whose name is the (i)-th lexicographic successor of the (N
+ r)-th variable binding's name in the incoming
GetBulkRequest-PDU is located and the variable binding's name
and value fields are set to the name and value of the located
variable.
(2) If there is no (i)-th lexicographic successor, then the
corresponding variable binding produced in the Response-PDU has
its value field set to "endOfMibView", and its name field set
to either the last lexicographic successor, or if there are no
lexicographic successors, to the (N + r)-th variable binding's
name in the request.
While the maximum number of variable bindings in the Response-PDU is
bounded by N + (M * R), the response may be generated with a lesser
number of variable bindings (possibly zero) for either of three
reasons.
(1) If the size of the message encapsulating the Response-PDU
containing the requested number of variable bindings would be
greater than either a local constraint or the maximum message
size of the originator, then the response is generated with a
lesser number of variable bindings. This lesser number is the
ordered set of variable bindings with some of the variable
bindings at the end of the set removed, such that the size of
the message encapsulating the Response-PDU is approximately
equal to but no greater than either a local constraint or the
maximum message size of the originator. Note that the number
of variable bindings removed has no relationship to the values
of N, M, or R.
(2) The response may also be generated with a lesser number of
variable bindings if for some value of iteration i, such that i
is greater than zero and less than or equal to M, that all of
the generated variable bindings have the value field set to
"endOfMibView". In this case, the variable bindings may be
truncated after the (N + (i * R))-th variable binding.
(3) In the event that the processing of a request with many
repetitions requires a significantly greater amount of
processing time than a normal request, then a command responder
application may terminate the request with less than the full
number of repetitions, providing at least one repetition is
completed.
Presuhn, et al. Standards Track [Page 16]
RFC 3416 Protocol Operations for SNMP December 2002
If the processing of any variable binding fails for a reason other
than listed above, then the Response-PDU is re-formatted with the
same values in its request-id and variable-bindings fields as the
received GetBulkRequest-PDU, with the value of its error-status field
set to "genErr", and the value of its error-index field is set to the
index of the variable binding in the original request which
corresponds to the failed variable binding.
Otherwise, the value of the Response-PDU's error-status field is set
to "noError", and the value of its error-index field to zero.
The generated Response-PDU (possibly with an empty variable-bindings
field) is then encapsulated into a message. If the size of the
resultant message is less than or equal to both a local constraint
and the maximum message size of the originator, it is transmitted to
the originator of the GetBulkRequest-PDU. Otherwise, the
snmpSilentDrops [RFC3418] counter is incremented and the resultant
message is discarded.
This example demonstrates how the GetBulkRequest-PDU can be used as
an alternative to the GetNextRequest-PDU. The same traversal of the
IP net-to-media table as shown in Section 4.2.2.1 is achieved with
fewer exchanges.
The SNMP entity supporting the command generator application begins
by sending a GetBulkRequest-PDU with the modest max-repetitions value
of 2, and containing the indicated OBJECT IDENTIFIER values as the
requested variable names:
GetBulkRequest [ non-repeaters = 1, max-repetitions = 2 ]
( sysUpTime,
ipNetToMediaPhysAddress,
ipNetToMediaType )
The SNMP entity supporting the command responder application responds
with a Response-PDU:
Response (( sysUpTime.0 = "123456" ),
( ipNetToMediaPhysAddress.1.9.2.3.4 = "000010543210" ),
( ipNetToMediaType.1.9.2.3.4 = "dynamic" ),
( ipNetToMediaPhysAddress.1.10.0.0.51 = "000010012345" ),
( ipNetToMediaType.1.10.0.0.51 = "static" ))
Presuhn, et al. Standards Track [Page 17]
RFC 3416 Protocol Operations for SNMP December 2002
The SNMP entity supporting the command generator application
continues with:
GetBulkRequest [ non-repeaters = 1, max-repetitions = 2 ]
( sysUpTime,
ipNetToMediaPhysAddress.1.10.0.0.51,
ipNetToMediaType.1.10.0.0.51 )
The SNMP entity supporting the command responder application responds
with:
Response (( sysUpTime.0 = "123466" ),
( ipNetToMediaPhysAddress.2.10.0.0.15 = "000010987654" ),
( ipNetToMediaType.2.10.0.0.15 = "dynamic" ),
( ipNetToMediaNetAddress.1.9.2.3.4 = "9.2.3.4" ),
( ipRoutingDiscards.0 = "2" ))
Note how, as in the first example, the variable bindings in the
response indicate that the end of the table has been reached. The
fourth variable binding does so by returning information from the
next available column; the fifth variable binding does so by
returning information from the first available object
lexicographically following the table. This response signals the end
of the table to the command generator application.
The Response-PDU is generated by an SNMP entity only upon receipt of
a GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU,
SetRequest-PDU, or InformRequest-PDU, as described elsewhere in this
document.
If the error-status field of the Response-PDU is non-zero, the value
fields of the variable bindings in the variable binding list are
ignored.
If both the error-status field and the error-index field of the
Response-PDU are non-zero, then the value of the error-index field is
the index of the variable binding (in the variable-binding list of
the corresponding request) for which the request failed. The first
variable binding in a request's variable-binding list is index one,
the second is index two, etc.
A compliant SNMP entity supporting a command generator application
must be able to properly receive and handle a Response-PDU with an
error-status field equal to "noSuchName", "badValue", or "readOnly".
(See sections 1.3 and 4.3 of [RFC2576].)
Presuhn, et al. Standards Track [Page 18]
RFC 3416 Protocol Operations for SNMP December 2002
Upon receipt of a Response-PDU, the receiving SNMP entity presents
its contents to the application which generated the request with the
same request-id value. For more details, see [RFC3412].
A SetRequest-PDU is generated and transmitted at the request of an
application.
Upon receipt of a SetRequest-PDU, the receiving SNMP entity
determines the size of a message encapsulating a Response-PDU having
the same values in its request-id and variable-bindings fields as the
received SetRequest-PDU, and the largest possible sizes of the
error-status and error-index fields. If the determined message size
is greater than either a local constraint or the maximum message size
of the originator, then an alternate Response-PDU is generated,
transmitted to the originator of the SetRequest-PDU, and processing
of the SetRequest-PDU terminates immediately thereafter. This
alternate Response-PDU is formatted with the same values in its
request-id field as the received SetRequest-PDU, with the value of
its error-status field set to "tooBig", the value of its error-index
field set to zero, and an empty variable-bindings field. This
alternate Response-PDU is then encapsulated into a message. If the
size of the resultant message is less than or equal to both a local
constraint and the maximum message size of the originator, it is
transmitted to the originator of the SetRequest-PDU. Otherwise, the
snmpSilentDrops [RFC3418] counter is incremented and the resultant
message is discarded. Regardless, processing of the SetRequest-PDU
terminates.
Otherwise, the receiving SNMP entity processes each variable binding
in the variable-binding list to produce a Response-PDU. All fields
of the Response-PDU have the same values as the corresponding fields
of the received request except as indicated below.
The variable bindings are conceptually processed as a two phase
operation. In the first phase, each variable binding is validated;
if all validations are successful, then each variable is altered in
the second phase. Of course, implementors are at liberty to
implement either the first, or second, or both, of these conceptual
phases as multiple implementation phases. Indeed, such multiple
implementation phases may be necessary in some cases to ensure
consistency.
Presuhn, et al. Standards Track [Page 19]
RFC 3416 Protocol Operations for SNMP December 2002
The following validations are performed in the first phase on each
variable binding until they are all successful, or until one fails:
(1) If the variable binding's name specifies an existing or non-
existent variable to which this request is/would be denied
access because it is/would not be in the appropriate MIB view,
then the value of the Response-PDU's error-status field is set
to "noAccess", and the value of its error-index field is set to
the index of the failed variable binding.
(2) Otherwise, if there are no variables which share the same
OBJECT IDENTIFIER prefix as the variable binding's name, and
which are able to be created or modified no matter what new
value is specified, then the value of the Response-PDU's
error-status field is set to "notWritable", and the value of
its error-index field is set to the index of the failed
variable binding.
(3) Otherwise, if the variable binding's value field specifies,
according to the ASN.1 language, a type which is inconsistent
with that required for all variables which share the same
OBJECT IDENTIFIER prefix as the variable binding's name, then
the value of the Response-PDU's error-status field is set to
"wrongType", and the value of its error-index field is set to
the index of the failed variable binding.
(4) Otherwise, if the variable binding's value field specifies,
according to the ASN.1 language, a length which is inconsistent
with that required for all variables which share the same
OBJECT IDENTIFIER prefix as the variable binding's name, then
the value of the Response-PDU's error-status field is set to
"wrongLength", and the value of its error-index field is set to
the index of the failed variable binding.
(5) Otherwise, if the variable binding's value field contains an
ASN.1 encoding which is inconsistent with that field's ASN.1
tag, then the value of the Response-PDU's error-status field is
set to "wrongEncoding", and the value of its error-index field
is set to the index of the failed variable binding. (Note that
not all implementation strategies will generate this error.)
(6) Otherwise, if the variable binding's value field specifies a
value which could under no circumstances be assigned to the
variable, then the value of the Response-PDU's error-status
field is set to "wrongValue", and the value of its error-index
field is set to the index of the failed variable binding.
Presuhn, et al. Standards Track [Page 20]
RFC 3416 Protocol Operations for SNMP December 2002
(7) Otherwise, if the variable binding's name specifies a variable
which does not exist and could not ever be created (even though
some variables sharing the same OBJECT IDENTIFIER prefix might
under some circumstances be able to be created), then the value
of the Response-PDU's error-status field is set to
"noCreation", and the value of its error-index field is set to
the index of the failed variable binding.
(8) Otherwise, if the variable binding's name specifies a variable
which does not exist but can not be created under the present
circumstances (even though it could be created under other
circumstances), then the value of the Response-PDU's error-
status field is set to "inconsistentName", and the value of its
error-index field is set to the index of the failed variable
binding.
(9) Otherwise, if the variable binding's name specifies a variable
which exists but can not be modified no matter what new value
is specified, then the value of the Response-PDU's error-status
field is set to "notWritable", and the value of its error-index
field is set to the index of the failed variable binding.
(10) Otherwise, if the variable binding's value field specifies a
value that could under other circumstances be held by the
variable, but is presently inconsistent or otherwise unable to
be assigned to the variable, then the value of the Response-
PDU's error-status field is set to "inconsistentValue", and the
value of its error-index field is set to the index of the
failed variable binding.
(11) When, during the above steps, the assignment of the value
specified by the variable binding's value field to the
specified variable requires the allocation of a resource which
is presently unavailable, then the value of the Response-PDU's
error-status field is set to "resourceUnavailable", and the
value of its error-index field is set to the index of the
failed variable binding.
(12) If the processing of the variable binding fails for a reason
other than listed above, then the value of the Response-PDU's
error-status field is set to "genErr", and the value of its
error-index field is set to the index of the failed variable
binding.
(13) Otherwise, the validation of the variable binding succeeds.
Presuhn, et al. Standards Track [Page 21]
RFC 3416 Protocol Operations for SNMP December 2002
At the end of the first phase, if the validation of all variable
bindings succeeded, then the value of the Response-PDU's error-status
field is set to "noError" and the value of its error-index field is
zero, and processing continues as follows.
For each variable binding in the request, the named variable is
created if necessary, and the specified value is assigned to it.
Each of these variable assignments occurs as if simultaneously with
respect to all other assignments specified in the same request.
However, if the same variable is named more than once in a single
request, with different associated values, then the actual assignment
made to that variable is implementation-specific.
If any of these assignments fail (even after all the previous
validations), then all other assignments are undone, and the
Response-PDU is modified to have the value of its error-status field
set to "commitFailed", and the value of its error-index field set to
the index of the failed variable binding.
If and only if it is not possible to undo all the assignments, then
the Response-PDU is modified to have the value of its error-status
field set to "undoFailed", and the value of its error-index field is
set to zero. Note that implementations are strongly encouraged to
take all possible measures to avoid use of either "commitFailed" or
"undoFailed" - these two error-status codes are not to be taken as
license to take the easy way out in an implementation.
Finally, the generated Response-PDU is encapsulated into a message,
and transmitted to the originator of the SetRequest-PDU.
An SNMPv2-Trap-PDU is generated and transmitted by an SNMP entity on
behalf of a notification originator application. The SNMPv2-Trap-PDU
is often used to notify a notification receiver application at a
logically remote SNMP entity that an event has occurred or that a
condition is present. There is no confirmation associated with this
notification delivery mechanism.
The destination(s) to which an SNMPv2-Trap-PDU is sent is determined
in an implementation-dependent fashion by the SNMP entity. The first
two variable bindings in the variable binding list of an SNMPv2-
Trap-PDU are sysUpTime.0 [RFC3418] and snmpTrapOID.0 [RFC3418]
respectively. If the OBJECTS clause is present in the invocation of
the corresponding NOTIFICATION-TYPE macro, then each corresponding
variable, as instantiated by this notification, is copied, in order,
Presuhn, et al. Standards Track [Page 22]
RFC 3416 Protocol Operations for SNMP December 2002
to the variable-bindings field. If any additional variables are
being included (at the option of the generating SNMP entity), then
each is copied to the variable-bindings field.
An InformRequest-PDU is generated and transmitted by an SNMP entity
on behalf of a notification originator application. The
InformRequest-PDU is often used to notify a notification receiver
application that an event has occurred or that a condition is
present. This is a confirmed notification delivery mechanism,
although there is, of course, no guarantee of delivery.
The destination(s) to which an InformRequest-PDU is sent is specified
by the notification originator application. The first two variable
bindings in the variable binding list of an InformRequest-PDU are
sysUpTime.0 [RFC3418] and snmpTrapOID.0 [RFC3418] respectively. If
the OBJECTS clause is present in the invocation of the corresponding
NOTIFICATION-TYPE macro, then each corresponding variable, as
instantiated by this notification, is copied, in order, to the
variable-bindings field. If any additional variables are being
included (at the option of the generating SNMP entity), then each is
copied to the variable-bindings field.
Upon receipt of an InformRequest-PDU, the receiving SNMP entity
determines the size of a message encapsulating a Response-PDU with
the same values in its request-id, error-status, error-index and
variable-bindings fields as the received InformRequest-PDU. If the
determined message size is greater than either a local constraint or
the maximum message size of the originator, then an alternate
Response-PDU is generated, transmitted to the originator of the
InformRequest-PDU, and processing of the InformRequest-PDU terminates
immediately thereafter. This alternate Response-PDU is formatted
with the same values in its request-id field as the received
InformRequest-PDU, with the value of its error-status field set to
"tooBig", the value of its error-index field set to zero, and an
empty variable-bindings field. This alternate Response-PDU is then
encapsulated into a message. If the size of the resultant message is
less than or equal to both a local constraint and the maximum message
size of the originator, it is transmitted to the originator of the
InformRequest-PDU. Otherwise, the snmpSilentDrops [RFC3418] counter
is incremented and the resultant message is discarded. Regardless,
processing of the InformRequest-PDU terminates.
Otherwise, the receiving SNMP entity:
(1) presents its contents to the appropriate application;
Presuhn, et al. Standards Track [Page 23]
RFC 3416 Protocol Operations for SNMP December 2002
(2) generates a Response-PDU with the same values in its request-id
and variable-bindings fields as the received InformRequest-PDU,
with the value of its error-status field set to "noError" and
the value of its error-index field set to zero; and
(3) transmits the generated Response-PDU to the originator of the
InformRequest-PDU.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
This document is the product of the SNMPv3 Working Group. Some
special thanks are in order to the following Working Group members:
Randy Bush
Jeffrey D. Case
Mike Daniele
Rob Frye
Lauren Heintz
Keith McCloghrie
Russ Mundy
David T. Perkins
Randy Presuhn
Aleksey Romanov
Juergen Schoenwaelder
Bert Wijnen
Presuhn, et al. Standards Track [Page 24]
RFC 3416 Protocol Operations for SNMP December 2002
This version of the document, edited by Randy Presuhn, was initially
based on the work of a design team whose members were:
Jeffrey D. Case
Keith McCloghrie
David T. Perkins
Randy Presuhn
Juergen Schoenwaelder
The previous versions of this document, edited by Keith McCloghrie,
was the result of significant work by four major contributors:
Jeffrey D. Case
Keith McCloghrie
Marshall T. Rose
Steven Waldbusser
Additionally, the contributions of the SNMPv2 Working Group to the
previous versions are also acknowledged. In particular, a special
thanks is extended for the contributions of:
Alexander I. Alten
Dave Arneson
Uri Blumenthal
Doug Book
Kim Curran
Jim Galvin
Maria Greene
Iain Hanson
Dave Harrington
Nguyen Hien
Jeff Johnson
Michael Kornegay
Deirdre Kostick
David Levi
Daniel Mahoney
Bob Natale
Brian O'Keefe
Andrew Pearson
Dave Perkins
Randy Presuhn
Aleksey Romanov
Shawn Routhier
Jon Saperia
Juergen Schoenwaelder
Bob Stewart
Presuhn, et al. Standards Track [Page 25]
RFC 3416 Protocol Operations for SNMP December 2002
Kaj Tesink
Glenn Waters
Bert Wijnen
The protocol defined in this document by itself does not provide a
secure environment. Even if the network itself is secure (for
example by using IPSec), there is no control as to who on the secure
network is allowed access to management information.
It is recommended that the implementors consider the security
features as provided by the SNMPv3 framework. Specifically, the use
of the User-based Security Model STD 62, RFC 3414 [RFC3414] and the
View-based Access Control Model STD 62, RFC 3415 [RFC3415] is
recommended.
It is then a customer/user responsibility to ensure that the SNMP
entity is properly configured so that:
- only those principals (users) having legitimate rights can
access or modify the values of any MIB objects supported by
that entity;
- the occurrence of particular events on the entity will be
communicated appropriately;
- the entity responds appropriately and with due credence to
events and information that have been communicated to it.
[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Structure of Management
Information Version 2 (SMIv2)", STD 58, RFC 2578, April
1999.
[RFC2579] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Textual Conventions for
SMIv2", STD 58, RFC 2579, April 1999.
Presuhn, et al. Standards Track [Page 26]
RFC 3416 Protocol Operations for SNMP December 2002
[RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Conformance Statements for
SMIv2", STD 58, RFC 2580, April 1999.
[RFC3411] Harrington, D., Presuhn, R. and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen,
"Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002.
[RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, RFC
3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "The User-Based Security
Model (USM) for Version 3 of the Simple Network
Management Protocol (SNMPv3)", STD 62, RFC 3414, December
2002.
[RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415, December
2002.
[RFC3417] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Transport Mappings for the Simple Network
Management Protocol", STD 62, RFC 3417, December 2002.
[RFC3418] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62, RFC
3418, December 2002.
[ASN1] Information processing systems - Open Systems
Interconnection - Specification of Abstract Syntax
Notation One (ASN.1), International Organization for
Standardization. International Standard 8824, December
1987.
[FRAG] Kent, C. and J. Mogul, "Fragmentation Considered
Harmful," Proceedings, ACM SIGCOMM '87, Stowe, VT, August
1987.
Presuhn, et al. Standards Track [Page 27]
RFC 3416 Protocol Operations for SNMP December 2002
[RFC1155] Rose, M. and K. McCloghrie, "Structure and Identification
of Management Information for TCP/IP-based Internets",
STD 16, RFC 1155, May 1990.
[RFC1157] Case, J., Fedor, M., Schoffstall, M. and J. Davin,
"Simple Network Management Protocol", STD 15, RFC 1157,
May 1990.
[RFC1212] Rose, M. and K. McCloghrie, "Concise MIB Definitions",
STD 16, RFC 1212, March 1991.
[RFC1213] McCloghrie, K. and M. Rose, Editors, "Management
Information Base for Network Management of TCP/IP-based
internets: MIB-II", STD 17, RFC 1213, March 1991.
[RFC1215] Rose, M., "A Convention for Defining Traps for use with
the SNMP", RFC 1215, March 1991.
[RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901,
January 1996.
[RFC2576] Frye, R., Levi, D., Routhier, S. and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3
of the Internet-Standard Network Management Framework",
RFC 2576, March 2000.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, June 2000.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, September 2000.
[RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
These are the changes from RFC 1905:
- Corrected spelling error in copyright statement;
- Updated copyright date;
- Updated with new editor's name and contact information;
- Added notice on intellectual property;
Presuhn, et al. Standards Track [Page 28]
RFC 3416 Protocol Operations for SNMP December 2002
- Cosmetic fixes to layout and typography;
- Added table of contents;
- Title changed;
- Updated document headers and footers;
- Deleted the old clause 2.3, entitled "Access to Management
Information";
- Changed the way in which request-id was defined, though with
the same ultimate syntax and semantics, to avoid coupling with
SMI. This does not affect the protocol in any way;
- Replaced the word "exception" with the word "error" in the old
clause 4.1. This does not affect the protocol in any way;
- Deleted the first two paragraphs of the old clause 4.2;
- Clarified the maximum number of variable bindings that an
implementation must support in a PDU. This does not affect the
protocol in any way;
- Replaced occurrences of "SNMPv2 application" with
"application";
- Deleted three sentences in old clause 4.2.3 describing the
handling of an impossible situation. This does not affect the
protocol in any way;
- Clarified the use of the SNMPv2-Trap-Pdu in the old clause
4.2.6. This does not affect the protocol in any way;
- Aligned description of the use of the InformRequest-Pdu in old
clause 4.2.7 with the architecture. This does not affect the
protocol in any way;
- Updated references;
- Re-wrote introduction clause;
- Replaced manager/agent/SNMPv2 entity terminology with
terminology from RFC 2571. This does not affect the protocol
in any way;
- Eliminated IMPORTS from the SMI, replaced with equivalent in-
line ASN.1. This does not affect the protocol in any way;
Presuhn, et al. Standards Track [Page 29]
RFC 3416 Protocol Operations for SNMP December 2002
- Added notes calling attention to two different manifestations
of reaching the end of a table in the table walk examples;
- Added content to security considerations clause;
- Updated ASN.1 comment on use of Report-PDU. This does not
affect the protocol in any way;
- Updated acknowledgments section;
- Included information on handling of BITS;
- Deleted spurious comma in ASN.1 definition of PDUs;
- Added abstract;
- Made handling of additional variable bindings in informs
consistent with that for traps. This was a correction of an
editorial oversight, and reflects implementation practice;
- Added reference to RFC 2914.
Randy Presuhn
BMC Software, Inc.
2141 North First Street
San Jose, CA 95131
USA
Phone: +1 408 546 1006
EMail: randy_presuhn@bmc.com
Presuhn, et al. Standards Track [Page 30]
RFC 3416 Protocol Operations for SNMP December 2002
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Presuhn, et al. Standards Track [Page 31]