RFC 3584
Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework
Network Working Group R. Frye Request for Comments: 3584 Vibrant Solutions BCP: 74 D. Levi Obsoletes: 2576 Nortel Networks Category: Best Current Practice S. Routhier Wind River Systems, Inc. B. Wijnen Lucent Technologies August 2003 Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework Status of this Memo This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.Abstract
The purpose of this document is to describe coexistence between version 3 of the Internet-standard Network Management Framework, (SNMPv3), version 2 of the Internet-standard Network Management Framework (SNMPv2), and the original Internet-standard Network Management Framework (SNMPv1). This document also describes how to convert MIB modules from SMIv1 format to SMIv2 format. This document obsoletes RFC 2576.
Table Of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. SNMPv1 . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. SNMPv2 . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. SNMPv3 . . . . . . . . . . . . . . . . . . . . . . . . 5 2. SMI and Management Information Mappings. . . . . . . . . . . 5 2.1. MIB Modules. . . . . . . . . . . . . . . . . . . . . . 6 2.1.1. Object Definitions . . . . . . . . . . . . . . 6 2.1.2. Trap and Notification Definitions . . . . . . 8 2.2. Compliance Statements. . . . . . . . . . . . . . . . . 9 2.3. Capabilities Statements. . . . . . . . . . . . . . . . 9 3. Translating Notification Parameters. . . . . . . . . . . . . 10 3.1. Translating SNMPv1 Notification Parameters to SNMPv2 Notification Parameters . . . . . . . . . . . . 11 3.2. Translating SNMPv2 Notification Parameters to SNMPv1 Notification Parameters . . . . . . . . . . . . 12 4. Approaches to Coexistence in a Multi-lingual Network . . . . 14 4.1. SNMPv1 and SNMPv2 Access to MIB Data . . . . . . . . . 14 4.2. Multi-lingual implementations. . . . . . . . . . . . . 15 4.2.1. Command Generator. . . . . . . . . . . . . . . 15 4.2.2. Command Responder. . . . . . . . . . . . . . . 16 4.2.2.1. Handling Counter64 . . . . . . . . . 16 4.2.2.2. Mapping SNMPv2 Exceptions. . . . . . 17 4.2.2.2.1. Mapping noSuchObject and noSuchInstance. . . . 18 4.2.2.2.2. Mapping endOfMibView. . . 18 4.2.2.3. Processing An SNMPv1 GetReques . . . 18 4.2.2.4. Processing An SNMPv1 GetNextRequest. 19 4.2.2.5. Processing An SNMPv1 SetRequest. . . 20 4.2.3. Notification Originator. . . . . . . . . . . . 21 4.2.4. Notification Receiver. . . . . . . . . . . . . 21 4.3. Proxy Implementations. . . . . . . . . . . . . . . . . 22 4.3.1. Upstream Version Greater Than Downstream Version. . . . . . . . . . . . . . . . . . . . 22 4.3.2. Upstream Version Less Than Downstream Version. 23 4.4. Error Status Mappings. . . . . . . . . . . . . . . . . 25 5. Message Processing Models and Security Models. . . . . . . . 26 5.1. Mappings . . . . . . . . . . . . . . . . . . . . . . . 26 5.2. The SNMPv1 MP Model and SNMPv1 Community-based Security Model . . . . . . . . . . . . . . . . . . . . 26 5.2.1. Processing An Incoming Request . . . . . . . . 27 5.2.2. Generating An Outgoing Response. . . . . . . . 29 5.2.3. Generating An Outgoing Notification. . . . . . 29 5.2.4. Proxy Forwarding Of Requests . . . . . . . . . 30 5.3. The SNMP Community MIB Module. . . . . . . . . . . . . 30 6. Intellectual Property Statement. . . . . . . . . . . . . . . 42 7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . 43
8. Security Considerations. . . . . . . . . . . . . . . . . . . 43 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 9.1. Normative References . . . . . . . . . . . . . . . . . 44 9.2. Informative References . . . . . . . . . . . . . . . . 46 Appendix A. Change Log. . . . . . . . . . . . . . . . . . . . . 47 A.1. Changes From RFC 2576 . . . . . . . . . . . . . . . . . 47 A.2. Changes Between RFC 1908 and RFC 2576 . . . . . . . . . 49 Editors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 511. Overview
The purpose of this document is to describe coexistence between version 3 of the Internet-standard Network Management Framework, termed the SNMP version 3 framework (SNMPv3), version 2 of the Internet-standard Network Management Framework, termed the SNMP version 2 framework (SNMPv2), and the original Internet-standard Network Management Framework (SNMPv1). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. There are four general aspects of coexistence described in this document. Each of these is described in a separate section: - Conversion of MIB documents between SMIv1 and SMIv2 formats is documented in section 2. - Mapping of notification parameters is documented in section 3. - Approaches to coexistence between entities which support the various versions of SNMP in a multi-lingual network is documented in section 4. This section addresses the processing of protocol operations in multi-lingual implementations, as well as behaviour of proxy implementations. - The SNMPv1 Message Processing Model and Community-Based Security Model, which provides mechanisms for adapting SNMPv1 into the View-Based Access Control Model (VACM) [20], is documented in section 5 (this section also addresses the SNMPv2c Message Processing Model and Community-Based Security Model).
1.1. SNMPv1
SNMPv1 is defined by these documents: - STD 15, RFC 1157 [RFC1157] which defines the Simple Network Management Protocol (SNMPv1), the protocol used for network access to managed objects. - STD 16, RFC 1155 [RFC1155] which defines the Structure of Management Information (SMIv1), the mechanisms used for describing and naming objects for the purpose of management. - STD 16, RFC 1212 [RFC1212] which defines a more concise description mechanism, which is wholly consistent with the SMIv1. - RFC 1215 [RFC1215] which defines a convention for defining Traps for use with the SMIv1. Note that throughout this document, the term 'SMIv1' is used. This term generally refers to the information presented in RFC 1155, RFC 1212, and RFC 1215.1.2. SNMPv2
SNMPv2 is defined by these documents: - STD 58, RFC 2578 which defines Version 2 of the Structure of Management Information (SMIv2) [RFC2578]. - STD 58, RFC 2579 which defines common MIB "Textual Conventions" [RFC2579]. - STD 58, RFC 2580 which defines Conformance Statements and requirements for defining agent and manager capabilities [RFC2580]. - STD 62, RFC 3416 which defines the Protocol Operations used in processing [RFC3416]. - STD 62, RFC 3417 which defines the Transport Mappings used "on the wire" [RFC3417]. - STD 62, RFC 3418 which defines the basic Management Information Base for monitoring and controlling some basic common functions of SNMP entities [RFC3418]. Note that SMIv2 as used throughout this document refers to the first three documents listed above (RFCs 2578, 2579, and 2580).
The following document augments the definition of SNMPv2: - RFC 1901 [RFC1901] is an Experimental definition for using SNMPv2 PDUs within a community-based message wrapper. This is referred to throughout this document as SNMPv2c.1.3. SNMPv3
SNMPv3 is defined by these documents: - STD 62, RFC 3411 which defines an Architecture for Describing SNMP Management Frameworks [RFC3411]. - STD 62, RFC 3412 which defines Message Processing and Dispatching [RFC3412]. - STD 62, RFC 3413 which defines various SNMP Applications [RFC3413]. - STD 62, RFC 3414 which defines the User-based Security Model (USM), providing for both Authenticated and Private (encrypted) SNMP messages [RFC3414]. - STD 62, RFC 3415 which defines the View-based Access Control Model (VACM), providing the ability to limit access to different MIB objects on a per-user basis [RFC3415]. SNMPv3 also uses the SNMPv2 definitions of RFCs 3416 through 3418 and the SMIv2 definitions of 2578 through 2580 described above. Note that text throughout this document that refers to SNMPv2 PDU types and protocol operations applies to both SNMPv2c and SNMPv3.2. SMI and Management Information Mappings
The SMIv2 approach towards describing collections of managed objects is nearly a proper superset of the approach defined in the SMIv1. For example, both approaches use an adapted subset of ASN.1 [ASN1] as the basis for a formal descriptive notation. Indeed, one might note that the SMIv2 approach largely codifies the existing practice for defining MIB modules, based on extensive experience with the SMIv1. The following sections consider the three areas: MIB modules, compliance statements, and capabilities statements.
2.1. MIB Modules
MIB modules defined using the SMIv1 may continue to be used with protocol versions which use SNMPv2 PDUs. However, for SMIv1 MIB modules to conform to the SMIv2, the following changes SHALL be made:2.1.1. Object Definitions
In general, conversion of a MIB module does not require the deprecation of the objects contained therein. If the definition of an object is truly inadequate for its intended purpose, the object SHALL be deprecated or obsoleted, otherwise deprecation is not required. (1) The IMPORTS statement MUST reference SNMPv2-SMI, instead of RFC1155-SMI and RFC-1212. (2) The MODULE-IDENTITY macro MUST be invoked immediately after any IMPORTs statement. (3) For any object with a SYNTAX clause value of Counter, the object MUST have the value of its SYNTAX clause changed to Counter32. (4) For any object with a SYNTAX clause value of Gauge, the object MUST have the value of its SYNTAX clause changed to Gauge32, or Unsigned32 where appropriate. (5) For all objects, the ACCESS clause MUST be replaced by a MAX- ACCESS clause. The value of the MAX-ACCESS clause SHALL be the same as that of the ACCESS clause unless some other value makes "protocol sense" as the maximal level of access for the object. In particular, object types for which instances can be explicitly created by a protocol set operation, SHALL have a MAX-ACCESS clause of "read-create". If the value of the ACCESS clause is "write-only", then the value of the MAX-ACCESS clause MUST be "read-write", and the DESCRIPTION clause SHALL note that reading this object will result in implementation-specific results. Note that in SMIv1, the ACCESS clause specifies the minimal required access, while in SMIv2, the MAX-ACCESS clause specifies the maximum allowed access. This should be considered when converting an ACCESS clause to a MAX-ACCESS clause. (6) For all objects, if the value of the STATUS clause is "mandatory" or "optional", the value MUST be replaced with "current", "deprecated", or "obsolete" depending on the current usage of such objects.
(7) For any object not containing a DESCRIPTION clause, the object
MUST have a DESCRIPTION clause defined.
(8) For any object corresponding to a conceptual row which does not
have an INDEX clause, the object MUST have either an INDEX
clause or an AUGMENTS clause defined.
(9) If any INDEX clause contains a reference to an object with a
syntax of NetworkAddress, then a new object MUST be created and
placed in this INDEX clause immediately preceding the object
whose syntax is NetworkAddress. This new object MUST have a
syntax of INTEGER, it MUST be not-accessible, and its value MUST
always be 1. The effect of this, and the preceding bullet, is
to allow one to convert a MIB module in SMIv1 format to one in
SMIv2 format, and then use it with the SNMPv1 protocol with no
impact to existing SNMPv1 agents and managers.
(10) For any object with a SYNTAX of NetworkAddress, the SYNTAX MUST
be changed to IpAddress. Note that the use of NetworkAddress in
new MIB documents is strongly discouraged (in fact, new MIB
documents should be written using SMIv2, which does not define
NetworkAddress).
(11) For any object containing a DEFVAL clause with an OBJECT
IDENTIFIER value which is expressed as a collection of sub-
identifiers, the value MUST be changed to reference a single
ASN.1 identifier. This may require defining a series of new
administrative assignments (OBJECT IDENTIFIERS) in order to
define the single ASN.1 identifier.
(12) One or more OBJECT-GROUPS MUST be defined, and related objects
MUST be collected into appropriate groups. Note that SMIv2
requires all OBJECT-TYPEs to be a member of at least one
OBJECT-GROUP.
(13) For any non-columnar object that is instanced as if it were
immediately subordinate to a conceptual row, the value of the
STATUS clause of that object MUST be changed to "obsolete".
(14) For any conceptual row object that is not immediately
subordinate to a conceptual table, the value of the STATUS
clause of that object (and all subordinate objects) MUST be
changed to "obsolete".
Other changes are desirable, but not necessary:
(1) Creation and deletion of conceptual rows is inconsistent using
the SMIv1. The SMIv2 corrects this. As such, if the MIB module
undergoes review early in its lifetime, and it contains
conceptual tables which allow creation and deletion of
conceptual rows, then the objects relating to those tables MAY
be deprecated and replaced with objects defined using the new
approach. The approach based on SMIv2 can be found in section 7
of RFC 2578 [RFC2578], and the RowStatus and StorageType
TEXTUAL-CONVENTIONs are described in section 2 of RFC 2579
[RFC2579].
(2) For any object with an integer-valued SYNTAX clause, in which
the corresponding INTEGER does not have a range restriction
(i.e., the INTEGER has neither a defined set of named-number
enumerations nor an assignment of lower- and upper-bounds on its
value), the object SHOULD have the value of its SYNTAX clause
changed to Integer32, or have an appropriate range specified.
(3) For any object with a string-valued SYNTAX clause, in which the
corresponding OCTET STRING does not have a size restriction
(i.e., the OCTET STRING has no assignment of lower- and upper-
bounds on its length), the bounds for the size of the object
SHOULD be defined.
(4) All textual conventions informally defined in the MIB module
SHOULD be redefined using the TEXTUAL-CONVENTION macro. Such a
change would not necessitate deprecating objects previously
defined using an informal textual convention.
(5) For any object which represents a measurement in some kind of
units, a UNITS clause SHOULD be added to the definition of that
object.
(6) For any conceptual row which is an extension of another
conceptual row, i.e., for which subordinate columnar objects
both exist and are identified via the same semantics as the
other conceptual row, an AUGMENTS clause SHOULD be used in place
of the INDEX clause for the object corresponding to the
conceptual row which is an extension.
2.1.2. Trap and Notification Definitions
If a MIB module is changed to conform to the SMIv2, then each
occurrence of the TRAP-TYPE macro MUST be changed to a corresponding
invocation of the NOTIFICATION-TYPE macro:
(1) The IMPORTS statement MUST NOT reference RFC-1215 [RFC1215], and MUST reference SNMPv2-SMI instead. (2) The ENTERPRISE clause MUST be removed. (3) The VARIABLES clause MUST be renamed to the OBJECTS clause. (4) A STATUS clause MUST be added, with an appropriate value. Normally the value should be 'current', although 'deprecated' or 'obsolete' may be used as needed. (5) The value of an invocation of the NOTIFICATION-TYPE macro is an OBJECT IDENTIFIER, not an INTEGER, and MUST be changed accordingly. Specifically, if the value of the ENTERPRISE clause is not 'snmp' then the value of the invocation SHALL be the value of the ENTERPRISE clause extended with two sub- identifiers, the first of which has the value 0, and the second has the value of the invocation of the TRAP-TYPE. If the value of the ENTERPRISE clause is 'snmp', then the value of the invocation of the NOTIFICATION-TYPE macro SHALL be mapped in the same manner as described in section 3.1 in this document. (6) A DESCRIPTION clause MUST be added, if not already present. (7) One or more NOTIFICATION-GROUPs MUST be defined, and related notifications MUST be collected into those groups. Note that SMIv2 requires that all NOTIFICATION-TYPEs be a member of at least one NOTIFICATION-GROUP.2.2. Compliance Statements
For those information modules which are "standards track", a corresponding invocation of the MODULE-COMPLIANCE macro and related OBJECT-GROUP and/or NOTIFICATION-GROUP macros MUST be included within the information module (or in a companion information module), and any commentary text in the information module which relates to compliance SHOULD be removed. Typically this editing can occur when the information module undergoes review. Note that a MODULE-COMPLIANCE statement is not required for a MIB document that is not on the standards track (for example, an enterprise MIB), though it may be useful in some circumstances to define a MODULE-COMPLIANCE statement for such a MIB document.2.3. Capabilities Statements
RFC 1303 [RFC1303] uses the MODULE-CONFORMANCE macro to describe an agent's capabilities with respect to one or more MIB modules.
Converting such a description for use with the SMIv2 requires these
changes:
(1) The macro name AGENT-CAPABILITIES MUST be used instead of
MODULE-CONFORMANCE.
(2) The STATUS clause MUST be added, with a value of 'current'.
(3) All occurrences of the CREATION-REQUIRES clause MUST either be
omitted if appropriate, or be changed such that the semantics
are consistent with RFC 2580 [RFC2580].
In order to ease coexistence, object groups defined in an SMIv1
compliant MIB module may be referenced by the INCLUDES clause of an
invocation of the AGENT-CAPABILITIES macro: upon encountering a
reference to an OBJECT IDENTIFIER subtree defined in an SMIv1 MIB
module, all leaf objects which are subordinate to the subtree and
have a STATUS clause value of mandatory are deemed to be INCLUDEd.
(Note that this method is ambiguous when different revisions of an
SMIv1 MIB have different sets of mandatory objects under the same
subtree; in such cases, the only solution is to rewrite the MIB using
the SMIv2 in order to define the object groups unambiguously.)
3. Translating Notification Parameters
This section describes how parameters used for generating
notifications are translated between the format used for SNMPv1
notification protocol operations and the format used for SNMPv2
notification protocol operations. The parameters used to generate a
notification are called 'notification parameters'. The format of
parameters used for SNMPv1 notification protocol operations is
referred to in this document as 'SNMPv1 notification parameters'.
The format of parameters used for SNMPv2 notification protocol
operations is referred to in this document as 'SNMPv2 notification
parameters'.
The situations where notification parameters MUST be translated are:
- When an entity generates a set of notification parameters in a
particular format, and the configuration of the entity indicates
that the notification must be sent using an SNMP message version
that requires the other format for notification parameters.
- When a proxy receives a notification that was sent using an SNMP
message version that requires one format of notification
parameters, and must forward the notification using an SNMP
message version that requires the other format of notification
parameters.
In addition, it MAY be desirable to translate notification parameters
in a notification receiver application in order to present
notifications to the end user in a consistent format.
Note that for the purposes of this section, the set of notification
parameters is independent of whether the notification is to be sent
as a trap or an inform.
SNMPv1 notification parameters consist of:
- An enterprise parameter (OBJECT IDENTIFIER).
- An agent-addr parameter (NetworkAddress).
- A generic-trap parameter (INTEGER).
- A specific-trap parameter (INTEGER).
- A time-stamp parameter (TimeTicks).
- A list of variable-bindings (VarBindList).
SNMPv2 notification parameters consist of:
- A sysUpTime parameter (TimeTicks). This appears in the first
variable-binding in an SNMPv2-Trap-PDU or InformRequest-PDU.
- An snmpTrapOID parameter (OBJECT IDENTIFIER). This appears in the
second variable-binding in an SNMPv2-Trap-PDU or InformRequest-
PDU, and is equal to the value portion of that variable-binding
(not the name portion, as both the name and value are OBJECT
IDENTIFIERs).
- A list of variable-bindings (VarBindList). This refers to all but
the first two variable-bindings in an SNMPv2-Trap-PDU or
InformRequest-PDU.
3.1. Translating SNMPv1 Notification Parameters to SNMPv2 Notification
Parameters
The following procedure describes how to translate SNMPv1
notification parameters into SNMPv2 notification parameters:
(1) The SNMPv2 sysUpTime parameter SHALL be taken directly from the
SNMPv1 time-stamp parameter.
(2) If the SNMPv1 generic-trap parameter is 'enterpriseSpecific(6)',
the SNMPv2 snmpTrapOID parameter SHALL be the concatenation of
the SNMPv1 enterprise parameter and two additional sub-
identifiers, '0', and the SNMPv1 specific-trap parameter.
(3) If the SNMPv1 generic-trap parameter is not
'enterpriseSpecific(6)', the SNMPv2 snmpTrapOID parameter SHALL
be the corresponding trap as defined in section 2 of RFC 3418
[RFC3418]:
generic-trap
parameter snmpTrapOID.0
============ =============
0 1.3.6.1.6.3.1.1.5.1 (coldStart)
1 1.3.6.1.6.3.1.1.5.2 (warmStart)
2 1.3.6.1.6.3.1.1.5.3 (linkDown)
3 1.3.6.1.6.3.1.1.5.4 (linkUp)
4 1.3.6.1.6.3.1.1.5.5 (authenticationFailure)
5 1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss)
(4) The SNMPv2 variable-bindings SHALL be the SNMPv1 variable-
bindings. In addition, if the translation is being performed by
a proxy in order to forward a received trap, three additional
variable-bindings will be appended, if these three additional
variable-bindings do not already exist in the SNMPv1 variable-
bindings. The name portion of the first additional variable
binding SHALL contain snmpTrapAddress.0, and the value SHALL
contain the SNMPv1 agent-addr parameter. The name portion of
the second additional variable binding SHALL contain
snmpTrapCommunity.0, and the value SHALL contain the value of
the community-string field from the received SNMPv1 message
which contained the SNMPv1 Trap-PDU. The name portion of the
third additional variable binding SHALL contain
snmpTrapEnterprise.0 [RFC3418], and the value SHALL be the
SNMPv1 enterprise parameter.
3.2. Translating SNMPv2 Notification Parameters to SNMPv1 Notification
Parameters
The following procedure describes how to translate SNMPv2
notification parameters into SNMPv1 notification parameters:
(1) The SNMPv1 enterprise parameter SHALL be determined as follows:
- If the SNMPv2 snmpTrapOID parameter is one of the standard
traps as defined in RFC 3418 [RFC3418], then the SNMPv1
enterprise parameter SHALL be set to the value of the
variable-binding in the SNMPv2 variable-bindings whose name is
snmpTrapEnterprise.0 if that variable-binding exists. If it
does not exist, the SNMPv1 enterprise parameter SHALL be set
to the value 'snmpTraps' as defined in RFC 3418 [RFC3418].
- If the SNMPv2 snmpTrapOID parameter is not one of the standard
traps as defined in RFC 3418 [RFC3418], then the SNMPv1
enterprise parameter SHALL be determined from the SNMPv2
snmpTrapOID parameter as follows:
- If the next-to-last sub-identifier of the snmpTrapOID value
is zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID value with the last 2 sub-identifiers removed,
otherwise
- If the next-to-last sub-identifier of the snmpTrapOID value
is non-zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID value with the last sub-identifier removed.
(2) The SNMPv1 agent-addr parameter SHALL be determined based on the
situation in which the translation occurs.
- If the translation occurs within a notification originator
application, and the notification is to be sent over IP, the
SNMPv1 agent-addr parameter SHALL be set to the IP address of
the SNMP entity in which the notification originator resides.
If the notification is to be sent over some other transport,
the SNMPv1 agent-addr parameter SHALL be set to 0.0.0.0.
- If the translation occurs within a proxy application, the
proxy must attempt to extract the original source of the
notification from the variable-bindings. If the SNMPv2
variable-bindings contains a variable binding whose name is
snmpTrapAddress.0, the agent-addr parameter SHALL be set to
the value of that variable binding. Otherwise, the SNMPv1
agent-addr parameter SHALL be set to 0.0.0.0.
(3) If the SNMPv2 snmpTrapOID parameter is one of the standard traps
as defined in RFC 3418 [RFC3418], the SNMPv1 generic-trap
parameter SHALL be set as follows:
snmpTrapOID.0 parameter generic-trap
=============================== ============
1.3.6.1.6.3.1.1.5.1 (coldStart) 0
1.3.6.1.6.3.1.1.5.2 (warmStart) 1
1.3.6.1.6.3.1.1.5.3 (linkDown) 2
1.3.6.1.6.3.1.1.5.4 (linkUp) 3
1.3.6.1.6.3.1.1.5.5 (authenticationFailure) 4
1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss) 5
Otherwise, the SNMPv1 generic-trap parameter SHALL be set to 6.
(4) If the SNMPv2 snmpTrapOID parameter is one of the standard traps
as defined in RFC 3418 [RFC3418], the SNMPv1 specific-trap
parameter SHALL be set to zero. Otherwise, the SNMPv1
specific-trap parameter SHALL be set to the last sub-identifier
of the SNMPv2 snmpTrapOID parameter.
(5) The SNMPv1 time-stamp parameter SHALL be taken directly from the
SNMPv2 sysUpTime parameter.
(6) The SNMPv1 variable-bindings SHALL be the SNMPv2 variable-
bindings (and note that the SNMPv2 variable-bindings do not
include the variable-bindings containing sysUpTime.0,
snmpTrapOID.0). Note, however, that if the SNMPv2 variable-
bindings contain any objects whose type is Counter64, the
translation to SNMPv1 notification parameters cannot be
performed. In this case, the notification cannot be encoded in
an SNMPv1 packet (and so the notification cannot be sent using
SNMPv1, see section 4.2.3 and section 4.3).
4. Approaches to Coexistence in a Multi-lingual Network
There are two basic approaches to coexistence in a multi-lingual
network, multi-lingual implementations and proxy implementations.
Multi-lingual implementations allow elements in a network to
communicate with each other using an SNMP version which both elements
support. This allows a multi-lingual implementation to communicate
with any mono-lingual implementation, regardless of the SNMP version
supported by the mono-lingual implementation.
Proxy implementations provide a mechanism for translating between
SNMP versions using a third party network element. This allows
network elements which support only a single, but different, SNMP
version to communicate with each other. Proxy implementations are
also useful for securing communications over an insecure link between
two locally secure networks.
4.1. SNMPv1 and SNMPv2 Access to MIB Data
Throughout section 4., this document refers to 'SNMPv1 Access to MIB
Data' and 'SNMPv2 Access to MIB Data'. These terms refer to the part
of an SNMP agent which actually accesses instances of MIB objects,
and which actually initiates generation of notifications.
Differences between the two types of access to MIB data are:
- Error-status values generated.
- Generation of exception codes.
- Use of the Counter64 data type.
- The format of parameters provided when a notification is
generated.
SNMPv1 access to MIB data may generate SNMPv1 error-status values,
will never generate exception codes nor use the Counter64 data type,
and will provide SNMPv1 format parameters for generating
notifications. Note also that SNMPv1 access to MIB data will
actually never generate a readOnly error (a noSuchName error would
always occur in the situation where one would expect a readOnly
error).
SNMPv2 access to MIB data may generate SNMPv2 error-status values,
may generate exception codes, may use the Counter64 data type, and
will provide SNMPv2 format parameters for generating notifications.
Note that SNMPv2 access to MIB data will never generate readOnly,
noSuchName, or badValue errors.
Note that a particular multi-lingual implementation may choose to
implement all access to MIB data as SNMPv2 access to MIB data, and
perform the translations described herein for SNMPv1-based
transactions.
Further, note that there is no mention of 'SNMPv3 access to MIB data'
in this document, as SNMPv3 uses SNMPv2 PDU types and protocol
operations.
4.2. Multi-lingual implementations
This approach requires an entity to support multiple SNMP message
versions. Typically this means supporting SNMPv1, SNMPv2c, and
SNMPv3 message versions. The behaviour of various types of SNMP
applications which support multiple message versions is described in
the following sections. This approach allows entities which support
multiple SNMP message versions to coexist with and communicate with
entities which support only a single SNMP message version.
4.2.1. Command Generator
A command generator must select an appropriate message version when
sending requests to another entity. One way to achieve this is to
consult a local database to select the appropriate message version.
In addition, a command generator MUST 'downgrade' GetBulk requests to
GetNext requests when selecting SNMPv1 as the message version for an
outgoing request. This is done by simply changing the operation type to GetNext, ignoring any non-repeaters and max-repetitions values, and setting error-status and error-index to zero.4.2.2. Command Responder
A command responder must be able to deal with both SNMPv1 and SNMPv2 access to MIB data. There are three aspects to dealing with this. A command responder must: - Deal correctly with SNMPv2 access to MIB data that returns a Counter64 value while processing an SNMPv1 message, - Deal correctly with SNMPv2 access to MIB data that returns one of the three exception values while processing an SNMPv1 message, and - Map SNMPv2 error codes returned from SNMPv2 access to MIB data into SNMPv1 error codes when processing an SNMPv1 message. Note that SNMPv1 error codes SHOULD NOT be used without any change when processing SNMPv2c or SNMPv3 messages, except in the case of proxy forwarding. Also, SNMPv1 access to MIB data SHOULD NOT be used when processing SNMPv2c or SNMPv3 messages. In the case of proxy forwarding, for backwards compatibility, SNMPv1 error codes may be used without any change in a forwarded SNMPv2c or SNMPv3 message. The following sections describe the behaviour of a command responder application which supports multiple SNMP message versions, and which uses SNMPv2 access to MIB data when processing an SNMPv1 message.4.2.2.1. Handling Counter64
The SMIv2 [RFC2578] defines one new syntax that is incompatible with SMIv1. This syntax is Counter64. All other syntaxes defined by SMIv2 are compatible with SMIv1. The impact on multi-lingual command responders is that they MUST NOT ever return a variable binding containing a Counter64 value in a response to a request that was received using the SNMPv1 message version. Multi-lingual command responders SHALL take the approach that object instances whose type is Counter64 are implicitly excluded from view when processing an SNMPv1 message. So: - On receipt of an SNMPv1 GetRequest-PDU containing a variable binding whose name field points to an object instance of type Counter64, a GetResponsePDU SHALL be returned, with an error-
status of noSuchName and the error-index set to the variable
binding that caused this error.
- On an SNMPv1 GetNextRequest-PDU, any object instance which
contains a syntax of Counter64 SHALL be skipped, and the next
accessible object instance that does not have the syntax of
Counter64 SHALL be retrieved. If no such object instance exists,
then an error-status of noSuchName SHALL be returned, and the
error-index SHALL be set to the variable binding that caused this
error.
- Any SNMPv1 request which contains a variable binding with a
Counter64 value is ill-formed, so the foregoing rules do not
apply. If that error is detected, a response SHALL NOT be
returned, since it would contain a copy of the ill-formed variable
binding. Instead, the offending PDU SHALL be discarded and the
counter snmpInASNParseErrs SHALL be incremented.
4.2.2.2. Mapping SNMPv2 Exceptions
SNMPv2 provides a feature called exceptions, which allow an SNMPv2
Response PDU to return as much management information as possible,
even when an error occurs. However, SNMPv1 does not support
exceptions, and so an SNMPv1 Response PDU cannot return any
management information, and can only return an error-status and an
error-index value.
When an SNMPv1 request is received, a command responder MUST check
any variable bindings returned using SNMPv2 access to MIB data for
exception values, and convert these exception values into SNMPv1
error codes.
The type of exception that can be returned when accessing MIB data
and the action taken depends on the type of SNMP request.
- For a GetRequest, a noSuchObject or noSuchInstance exception may
be returned.
- For a GetNextRequest, an endOfMibView exception may be returned.
- No exceptions will be returned for a SetRequest, and a
GetBulkRequest should only be received in an SNMPv2c or SNMPv3
message, so these request types may be ignored when mapping
exceptions.
Note that when a response contains multiple exceptions, it is an
implementation choice as to which variable binding the error-index
should reference.
4.2.2.2.1. Mapping noSuchObject and noSuchInstance
A noSuchObject or noSuchInstance exception generated by an SNMPv2 access to MIB data indicates that the requested object instance can not be returned. The SNMPv1 error code for this condition is noSuchName, and so the error-status field of the response PDU SHALL be set to noSuchName. Also, the error-index field SHALL be set to the index of the variable binding for which an exception occurred (if there is more than one then it is an implementation decision as to which is used), and the variable binding list from the original request SHALL be returned with the response PDU.4.2.2.2.2. Mapping endOfMibView
When an SNMPv2 access to MIB data returns a variable binding containing an endOfMibView exception, it indicates that there are no object instances available which lexicographically follow the object in the request. In an SNMPv1 agent, this condition normally results in a noSuchName error, and so the error-status field of the response PDU SHALL be set to noSuchName. Also, the error-index field SHALL be set to the index of the variable binding for which an exception occurred (if there is more than one then it is an implementation decision as to which is used), and the variable binding list from the original request SHALL be returned with the response PDU.4.2.2.3. Processing An SNMPv1 GetRequest
When processing an SNMPv1 GetRequest, the following procedures MUST be followed when using an SNMPv2 access to MIB data. When such an access to MIB data returns response data using SNMPv2 syntax and error-status values, then: (1) If the error-status is anything other than noError, - The error status SHALL be translated to an SNMPv1 error- status using the table in section 4.4, "Error Status Mappings". - The error-index SHALL be set to the position (in the original request) of the variable binding that caused the error-status. - The variable binding list of the response PDU SHALL be made exactly the same as the variable binding list that was received in the original request.
(2) If the error-status is noError, the variable bindings SHALL be
checked for any SNMPv2 exception (noSuchObject or
noSuchInstance) or an SNMPv2 syntax that is unknown to SNMPv1
(Counter64). If there are any such variable bindings, one of
those variable bindings SHALL be selected (it is an
implementation choice as to which is selected), and:
- The error-status SHALL be set to noSuchName,
- The error-index SHALL be set to the position (in the
variable binding list of the original request) of the
selected variable binding, and
- The variable binding list of the response PDU SHALL be
exactly the same as the variable binding list that was
received in the original request.
(3) If there are no such variable bindings, then:
- The error-status SHALL be set to noError,
- The error-index SHALL be set to zero, and
- The variable binding list of the response SHALL be composed
from the data as it is returned by the access to MIB data.
4.2.2.4. Processing An SNMPv1 GetNextRequest
When processing an SNMPv1 GetNextRequest, the following procedures
MUST be followed when SNMPv2 access to MIB data is used as part of
processing the request. There may be repetitive accesses to MIB data
to try to find the first object which lexicographically follows each
of the objects in the request. This is implementation specific.
These procedures are followed only for data returned when using
SNMPv2 access to MIB data. Data returned using SNMPv1 access to MIB
data may be treated in the normal manner for an SNMPv1 request.
First, if the access to MIB data returns an error-status of anything
other than noError:
(1) The error status SHALL be translated to an SNMPv1 error-status
using the table in section 4.4, "Error Status Mappings".
(2) The error-index SHALL be set to the position (in the original
request) of the variable binding that caused the error-status.
(3) The variable binding list of the response PDU SHALL be exactly
the same as the variable binding list that was received in the
original request.
Otherwise, if the access to MIB data returns an error-status of
noError:
(1) Any variable bindings containing an SNMPv2 syntax of Counter64
SHALL be considered to be not in view, and MIB data SHALL be
accessed as many times as is required until either a value other
than Counter64 is returned, or an error or endOfMibView
exception occurs.
(2) If there is any variable binding that contains an SNMPv2
exception endOfMibView (if there is more than one then it is an
implementation decision as to which is chosen):
- The error-status SHALL be set to noSuchName,
- The error-index SHALL be set to the position (in the
variable binding list of the original request) of the
variable binding that returned such an SNMPv2 exception, and
- The variable binding list of the response PDU SHALL be
exactly the same as the variable binding list that was
received in the original request.
(3) If there are no such variable bindings, then:
- The error-status SHALL be set to noError,
- The error-index SHALL be set to zero, and
- The variable binding list of the response SHALL be composed
from the data as it is returned by the access to MIB data.
4.2.2.5. Processing An SNMPv1 SetRequest
When processing an SNMPv1 SetRequest, the following procedures MUST
be followed when using SNMPv2 access to MIB data.
When such MIB access returns response data using SNMPv2 syntax and
error-status values, and the error-status is anything other than
noError, then:
- The error status SHALL be translated to an SNMPv1 error-status
using the table in section 4.4, "Error Status Mappings".
- The error-index SHALL be set to the position (in the original
request) of the variable binding that caused the error-status.
- The variable binding list of the response PDU SHALL be made
exactly the same as the variable binding list that was received in
the original request.
4.2.3. Notification Originator
A notification originator must be able to translate between SNMPv1
notification parameters and SNMPv2 notification parameters in order
to send a notification using a particular SNMP message version. If a
notification is generated using SNMPv1 notification parameters, and
configuration information specifies that notifications be sent using
SNMPv2c or SNMPv3, the notification parameters must be translated to
SNMPv2 notification parameters. Likewise, if a notification is
generated using SNMPv2 notification parameters, and configuration
information specifies that notifications be sent using SNMPv1, the
notification parameters must be translated to SNMPv1 notification
parameters. In this case, if the notification cannot be translated
(due to the presence of a Counter64 type), it will not be sent using
SNMPv1.
When a notification originator generates a notification, using
parameters obtained from the SNMP-TARGET-MIB and SNMP-NOTIFICATION-
MIB, if the SNMP version used to generate the notification is SNMPv1,
the PDU type used will always be a TrapPDU, regardless of whether the
value of snmpNotifyType is trap(1) or inform(2).
Note also that access control and notification filtering are
performed in the usual manner for notifications, regardless of the
SNMP message version to be used when sending a notification. The
parameters for performing access control are found in the usual
manner (i.e., from inspecting the SNMP-TARGET-MIB and SNMP-
NOTIFICATION-MIB). In particular, when generating an SNMPv1 Trap, in
order to perform the access check specified in [RFC3413], section
3.3, bullet (3), the notification originator may need to generate a
value for snmpTrapOID.0 as described in section 3.1, bullets (2) and
(3) of this document. If the SNMPv1 notification parameters being
used were previously translated from a set of SNMPv2 notification
parameters, this value may already be known, in which case it need
not be generated.
4.2.4. Notification Receiver
There are no special requirements of a notification receiver.
However, an implementation may find it useful to allow a higher level
application to request whether notifications should be delivered to a
higher level application using SNMPv1 notification parameter or SNMPv2 notification parameters. The notification receiver would then translate notification parameters when required in order to present a notification using the desired set of parameters.4.3. Proxy Implementations
A proxy implementation may be used to enable communication between entities which support different SNMP message versions. This is accomplished in a proxy forwarder application by performing translations on PDUs. These translations depend on the PDU type, the SNMP version of the packet containing a received PDU, and the SNMP version to be used to forward a received PDU. The following sections describe these translations. In all cases other than those described below, the proxy SHALL forward a received PDU without change, subject to size constraints as defined in section 5.3 (Community MIB) of this document. Note that in the following sections, the 'Upstream Version' refers to the version used between the command generator or notification receiver and the proxy, and the 'Downstream Version' refers to the version used between the proxy and the command responder or notification originator, regardless of the PDU type or direction.4.3.1. Upstream Version Greater Than Downstream Version
- If a GetBulkRequest-PDU is received and must be forwarded using the SNMPv1 message version, the proxy forwarder SHALL act as if the non-repeaters and max-repetitions fields were both set to 0, and SHALL set the tag of the PDU to GetNextRequest-PDU. - If a GetResponse-PDU is received whose error-status field has a value of 'tooBig', and the message will be forwarded using the SNMPv2c or SNMPv3 message version, and the original request received by the proxy was not a GetBulkRequest-PDU, the proxy forwarder SHALL remove the contents of the variable-bindings field and ensure that the error-index field is set to 0 before forwarding the response. - If a GetResponse-PDU is received whose error-status field has a value of 'tooBig', and the message will be forwarded using the SNMPv2c or SNMPv3 message version, and the original request received by the proxy was a GetBulkRequest-PDU, the proxy forwarder SHALL re-send the forwarded request (which would have been altered to be a GetNextRequest-PDU) with all but the first variable-binding removed. The proxy forwarder SHALL only re-send such a request a single time. If the resulting GetResponse-PDU also contains an error-status field with a value of 'tooBig', then the proxy forwarder SHALL remove the contents of the variable-
bindings field, and change the error-status field to 'noError',
and ensure that the error-index field is set to 0 before
forwarding the response. Note that if the original request only
contained a single variable-binding, the proxy may skip re-sending
the request and simply remove the variable-bindings and change the
error-status to 'noError'. Further note that, while it might have
been possible to fit more variable bindings if the proxy only re-
sent the request multiple times, and stripped only a single
variable binding from the request at a time, this is deemed too
expensive. The approach described here preserves the behaviour of
a GetBulkRequest as closely as possible, without incurring the
cost of re-sending the request multiple times.
- If a Trap-PDU is received, and will be forwarded using the SNMPv2c
or SNMPv3 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as an SNMPv2-Trap-PDU.
Note that when an SNMPv1 agent generates a message containing a
Trap-PDU which is subsequently forwarded by one or more proxy
forwarders using SNMP versions other than SNMPv1, the community
string and agent-addr fields from the original message generated
by the SNMPv1 agent will be preserved through the use of the
snmpTrapAddress and snmpTrapCommunity objects.
4.3.2. Upstream Version Less Than Downstream Version
- If a GetResponse-PDU is received in response to a GetRequest-PDU
(previously generated by the proxy) which contains variable-
bindings of type Counter64 or which contain an SNMPv2 exception
code, and the message would be forwarded using the SNMPv1 message
version, the proxy MUST generate an alternate response PDU
consisting of the request-id and variable bindings from the
original SNMPv1 request, containing a noSuchName error-status
value, and containing an error-index value indicating the position
of the variable-binding containing the Counter64 type or exception
code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings that contain an SNMPv2 exception code, and the message
would be forwarded using the SNMPv1 message version, the proxy
MUST generate an alternate response PDU consisting of the
request-id and variable bindings from the original SNMPv1 request,
containing a noSuchName error-status value, and containing an
error-index value indicating the position of the variable-binding
containing the exception code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings of type Counter64, the proxy MUST re-send the entire
GetNextRequest-PDU, with the following modifications. For any
variable bindings in the received GetResponse which contained
Counter64 types, the proxy substitutes the object names of these
variable bindings for the corresponding object names in the
previously-sent GetNextRequest. The proxy MUST repeat this
process until no Counter64 objects are returned. Note that an
implementation may attempt to optimize this process of skipping
Counter64 objects. One approach to such an optimization would be
to replace the last sub-identifier of the object names of varbinds
containing a Counter64 type with 65535 if that sub-identifier is
less than 65535, or with 4294967295 if that sub-identifier is
greater than 65535. This approach should skip multiple instances
of the same Counter64 object, while maintaining compatibility with
some broken agent implementations (which only use 16-bit integers
for sub-identifiers).
Deployment Hint: The process of repeated GetNext requests used by
a proxy when Counter64 types are returned can be expensive. When
deploying a proxy, this can be avoided by configuring the target
agents to which the proxy forwards requests in a manner such that
any objects of type Counter64 are in fact not-in-view for the
principal that the proxy is using when communicating with these
agents. However, when using such a configuration, one should be
careful to use a different principal for communicating with the
target agent when an incoming SNMPv2c or SNMPv3 request is
received, to ensure that objects of type Counter64 are properly
returned.
- If a GetResponse-PDU is received which contains an SNMPv2 error-
status value of wrongValue, wrongEncoding, wrongType, wrongLength,
inconsistentValue, noAccess, notWritable, noCreation,
inconsistentName, resourceUnavailable, commitFailed, undoFailed,
or authorizationError, and the message would be forwarded using
the SNMPv1 message version, the error-status value is modified
using the mappings in section 4.4.
- If an SNMPv2-Trap-PDU is received, and will be forwarded using the
SNMPv1 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as a Trap-PDU. Note that if the translation fails due to the
existence of a Counter64 data-type in the received SNMPv2-Trap-
PDU, the trap cannot be forwarded using SNMPv1.
- If an InformRequest-PDU is received, any configuration information
indicating that it would be forwarded using the SNMPv1 message
version SHALL be ignored. An InformRequest-PDU can only be
forwarded using the SNMPv2c or SNMPv3 message version. The
InformRequest-PDU may still be forwarded if there is other
configuration information indicating that it should be forwarded
using SNMPv2c or SNMPv3.
4.4. Error Status Mappings
The following tables shows the mappings of SNMPv1 error-status values
into SNMPv2 error-status values, and the mappings of SNMPv2 error-
status values into SNMPv1 error-status values.
SNMPv1 error-status SNMPv2 error-status
=================== ===================
noError noError
tooBig tooBig
noSuchName noSuchName
badValue badValue
genErr genErr
SNMPv2 error-status SNMPv1 error-status
=================== ===================
noError noError
tooBig tooBig
genErr genErr
wrongValue badValue
wrongEncoding badValue
wrongType badValue
wrongLength badValue
inconsistentValue badValue
noAccess noSuchName
notWritable noSuchName
noCreation noSuchName
inconsistentName noSuchName
resourceUnavailable genErr
commitFailed genErr
undoFailed genErr
authorizationError noSuchName
Whenever the SNMPv2 error-status value of authorizationError is
translated to an SNMPv1 error-status value of noSuchName, the value
of snmpInBadCommunityUses MUST be incremented.