📄 rfc2576.txt
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- 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.
- A list of variable-bindings (VarBindList). This refers to all
but the first two variable-bindings in an SNMPv2-Trap-PDU or
InformRequest-PDU.
Frye, et al. Standards Track [Page 11]
RFC 2576 Coexistence between SNMP versions March 2000
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 concatentation 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 RFC1907
[12]:
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 [12], and the value SHALL be the SNMPv1
enterprise parameter.
Frye, et al. Standards Track [Page 12]
RFC 2576 Coexistence between SNMP versions March 2000
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 RFC1907 [12], 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 RFC1907 [12].
- If the SNMPv2 snmpTrapOID parameter is not one of the standard
traps as defined in RFC1907 [12], 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 is
zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID with the last 2 sub-identifiers removed,
otherwise
- If the next-to-last sub-identifier of the snmpTrapOID is
non-zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID 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.
Frye, et al. Standards Track [Page 13]
RFC 2576 Coexistence between SNMP versions March 2000
(3) If the SNMPv2 snmpTrapOID parameter is one of the standard traps
as defined in RFC1907 [12], 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 RFC1907 [12], 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. 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 4.1.3 and section 4.2).
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.
Frye, et al. Standards Track [Page 14]
RFC 2576 Coexistence between SNMP versions March 2000
4.1. 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.
4.1.1. 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.
4.1.2. 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. 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 some combination of SNMPv1 and SNMPv2 access to MIB data.
Frye, et al. Standards Track [Page 15]
RFC 2576 Coexistence between SNMP versions March 2000
4.1.2.1. Handling Counter64
The SMIv2 [7] 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.
4.1.2.2. 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
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