A MIB designer should choose between the two latter
algorithms based on the size of the table (and therefore the
efficiency of each algorithm). For tables in which a large
number of entries are expected, it is recommended that a MIB
object be defined that returns an acceptable index for
creation. For tables with small numbers of entries, it is
recommended that the latter pseudo-random index mechanism be
used.
Interaction 2: Creating the Conceptual Row
Once an unused instance-identifier has been selected, the
management station determines if it wishes to create and
activate the conceptual row in one transaction or in a
negotiated set of interactions.
Interaction 2a: Creating and Activating the Conceptual Row
The management station must first determine the column
requirements, i.e., it must determine those columns for
which it must or must not provide values. Depending on the
complexity of the table and the management station’s
knowledge of the agent’s capabilities, this determination
can be made locally by the management station. Alternately,
the management station issues a management protocol get
operation to examine all columns in the conceptual row that
it wishes to create. In response, for each column, there
are three possible outcomes:
- a value is returned, indicating that some other
management station has already created this conceptual
row. We return to interaction 1.
- the exception `noSuchInstance’ is returned,
indicating that the agent implements the object-type
associated with this column, and that this column in at
least one conceptual row would be accessible in the MIB
view used by the retrieval were it to exist. For those
columns to which the agent provides read-create access,
the `noSuchInstance’ exception tells the management
station that it should supply a value for this column
when the conceptual row is to be created.
- the exception `noSuchObject’ is returned, indicating
that the agent does not implement the object-type
associated with this column or that there is no
conceptual row for which this column would be
accessible in the MIB view used by the retrieval. As
such, the management station can not issue any
management protocol set operations to create an
instance of this column.
Once the column requirements have been determined, a
management protocol set operation is accordingly issued.
This operation also sets the new instance of the status
column to `createAndGo’.
When the agent processes the set operation, it verifies that
it has sufficient information to make the conceptual row
available for use by the managed device. The information
available to the agent is provided by two sources: the
management protocol set operation which creates the
conceptual row, and, implementation-specific defaults
supplied by the agent (note that an agent must provide
implementation-specific defaults for at least those objects
which it implements as read-only). If there is sufficient
information available, then the conceptual row is created, a
`noError’ response is returned, the status column is set to
`active’, and no further interactions are necessary (i.e.,
interactions 3 and 4 are skipped). If there is insufficient
information, then the conceptual row is not created, and the
set operation fails with an error of `inconsistentValue’.
On this error, the management station can issue a management
protocol retrieval operation to determine if this was
because it failed to specify a value for a required column,
or, because the selected instance of the status column
already existed. In the latter case, we return to
interaction 1. In the former case, the management station
can re-issue the set operation with the additional
information, or begin interaction 2 again using
`createAndWait’ in order to negotiate creation of the
conceptual row.
NOTE WELL
Regardless of the method used to determine the column
requirements, it is possible that the management
station might deem a column necessary when, in fact,
the agent will not allow that particular columnar
instance to be created or written. In this case, the
management protocol set operation will fail with an
error such as `noCreation’ or `notWritable’. In this
case, the management station decides whether it needs
to be able to set a value for that particular columnar
instance. If not, the management station re-issues the
management protocol set operation, but without setting
a value for that particular columnar instance;
otherwise, the management station aborts the row
creation algorithm.
Interaction 2b: Negotiating the Creation of the Conceptual
Row
The management station issues a management protocol set
operation which sets the desired instance of the status
column to `createAndWait’. If the agent is unwilling to
process a request of this sort, the set operation fails with
an error of `wrongValue’. (As a consequence, such an agent
must be prepared to accept a single management protocol set
operation, i.e., interaction 2a above, containing all of the
columns indicated by its column requirements.) Otherwise,
the conceptual row is created, a `noError’ response is
returned, and the status column is immediately set to either
`notInService’ or `notReady’, depending on whether it has
sufficient information to make the conceptual row available
for use by the managed device. If there is sufficient
information available, then the status column is set to
`notInService’; otherwise, if there is insufficient
information, then the status column is set to `notReady’.
Regardless, we proceed to interaction 3.
Interaction 3: Initializing non-defaulted Objects
The management station must now determine the column
requirements. It issues a management protocol get operation
to examine all columns in the created conceptual row. In
the response, for each column, there are three possible
outcomes:
- a value is returned, indicating that the agent
implements the object-type associated with this column
and had sufficient information to provide a value. For
those columns to which the agent provides read-create
access (and for which the agent allows their values to
be changed after their creation), a value return tells
the management station that it may issue additional
management protocol set operations, if it desires, in
order to change the value associated with this column.
- the exception `noSuchInstance’ is returned,
indicating that the agent implements the object-type
associated with this column, and that this column in at
least one conceptual row would be accessible in the MIB
view used by the retrieval were it to exist. However,
the agent does not have sufficient information to
provide a value, and until a value is provided, the
conceptual row may not be made available for use by the
managed device. For those columns to which the agent
provides read-create access, the `noSuchInstance’
exception tells the management station that it must
issue additional management protocol set operations, in
order to provide a value associated with this column.
- the exception `noSuchObject’ is returned, indicating
that the agent does not implement the object-type
associated with this column or that there is no
conceptual row for which this column would be
accessible in the MIB view used by the retrieval. As
such, the management station can not issue any
management protocol set operations to create an
instance of this column.
If the value associated with the status column is
`notReady’, then the management station must first deal with
all `noSuchInstance’ columns, if any. Having done so, the
value of the status column becomes `notInService’, and we
proceed to interaction 4.
Interaction 4: Making the Conceptual Row Available
Once the management station is satisfied with the values
associated with the columns of the conceptual row, it issues
a management protocol set operation to set the status column
to `active’. If the agent has sufficient information to
make the conceptual row available for use by the managed
device, the management protocol set operation succeeds (a
`noError’ response is returned). Otherwise, the management
protocol set operation fails with an error of
`inconsistentValue’.
NOTE WELL
A conceptual row having a status column with value
`notInService’ or `notReady’ is unavailable to the
managed device. As such, it is possible for the
managed device to create its own instances during the
time between the management protocol set operation
which sets the status column to `createAndWait’ and the
management protocol set operation which sets the status
column to `active’. In this case, when the management
protocol set operation is issued to set the status
column to `active’, the values held in the agent
supersede those used by the managed device.
If the management station is prevented from setting the
status column to `active’ (e.g., due to management station or
network failure) the conceptual row will be left in the
`notInService’ or `notReady’ state, consuming resources
indefinitely. The agent must detect conceptual rows that
have been in either state for an abnormally long period of
time and remove them. It is the responsibility of the
DESCRIPTION clause of the status column to indicate what an
abnormally long period of time would be. This period of time
should be long enough to allow for human response time
(including `think time’) between the creation of the
conceptual row and the setting of the status to `active’. In
the absence of such information in the DESCRIPTION clause, it
is suggested that this period be approximately 5 minutes in
length. This removal action applies not only to newly-
created rows, but also to previously active rows which are
set to, and left in, the notInService state for a prolonged
period exceeding that which is considered normal for such a
conceptual row.
Conceptual Row Suspension
When a conceptual row is `active’, the management station
may issue a management protocol set operation which sets the
instance of the status column to `notInService’. If the
agent is unwilling to do so, the set operation fails with an
error of `wrongValue’ or `inconsistentValue’.
Otherwise, the conceptual row is taken out of service, and a
`noError’ response is returned. It is the responsibility of
the DESCRIPTION clause of the status column to indicate
under what circumstances the status column should be taken
out of service (e.g., in order for the value of some other
column of the same conceptual row to be modified).
Conceptual Row Deletion
For deletion of conceptual rows, a management protocol set
operation is issued which sets the instance of the status
column to `destroy’. This request may be made regardless of
the current value of the status column (e.g., it is possible
to delete conceptual rows which are either `notReady’,
`notInService’ or `active’.) If the operation succeeds, then
all instances associated with the conceptual row are
immediately removed.";
};
typedef StorageType {
type Enumeration (other(1), volatile(2),
nonVolatile(3), permanent(4),
readOnly(5));
description
"Describes the memory realization of a conceptual row. A
row which is volatile(2) is lost upon reboot. A row
which is either nonVolatile(3), permanent(4) or
readOnly(5), is backed up by stable storage. A row which
is permanent(4) can be changed but not deleted. A row
which is readOnly(5) cannot be changed nor deleted.
If the value of an object with this syntax is either
permanent(4) or readOnly(5), it cannot be modified.
Conversely, if the value is either other(1), volatile(2)
or nonVolatile(3), it cannot be modified to be
permanent(4) or readOnly(5). (All illegal modifications
result in a ’wrongValue’ error.)
Every usage of this textual convention is required to
specify the columnar objects which a permanent(4) row
must at a minimum allow to be writable.";
};
typedef TDomain {
type Pointer;
description
"Denotes a kind of transport service.
Some possible values, such as snmpUDPDomain, are defined
in the SNMPv2-TM MIB module. Other possible values are
defined in other MIB modules."
reference
"The SNMPv2-TM MIB module is defined in RFC 3417."
};
typedef TAddressOrZero {
type OctetString (0..255);
description
"Denotes a transport service address.
A TAddress value is always interpreted within the context
of a TDomain value. Thus, each definition of a TDomain
value must be accompanied by a definition of a textual
convention for use with that TDomain. Some possible
textual conventions, such as SnmpUDPAddress for
snmpUDPDomain, are defined in the SNMPv2-TM MIB module.
Other possible textual conventions are defined in other
MIB modules.
A zero-length TAddress value denotes an unknown transport
service address."
reference
"The SNMPv2-TM MIB module is defined in RFC 3417."
};
typedef TAddress {
type TAddressOrZero (1..255);
description
"Denotes a transport service address.
This type does not allow a zero-length TAddress value."
};
};
7. Security Considerations
This document presents an extension of the SMIng data definition
language which supports the mapping of SMIng data definitions so that
they can be used with the SNMP management framework. The language
extension and the mapping itself has no security impact on the
Internet.
8. Acknowledgements
Since SMIng started as a close successor of SMIv2, some paragraphs
and phrases are directly taken from the SMIv2 specifications
[RFC2578], [RFC2579], [RFC2580] written by Jeff Case, Keith
McCloghrie, David Perkins, Marshall T. Rose, Juergen Schoenwaelder,
and Steven L. Waldbusser.
The authors would like to thank all participants of the 7th NMRG
meeting held in Schloss Kleinheubach from 6-8 September 2000, which
was a major step towards the current status of this memo, namely
Heiko Dassow, David Durham, Keith McCloghrie, and Bert Wijnen.
Furthermore, several discussions within the SMING Working Group
reflected experience with SMIv2 and influenced this specification at
some points.
9. References
9.1. Normative References
[RFC3780] Strauss, F. and J. Schoenwaelder, "SMIng - Next Generation
Structure of Management Information", RFC 3780, May 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
9.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet
Standard Management Framework", RFC 3410, December 2002.
[RFC2578] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Structure of Management Information Version 2 (SMIv2)",
STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Textual
Conventions for SMIv2", STD 59, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 60, RFC 2580,
April 1999.
[ASN1] International Organization for Standardization,
"Specification of Abstract Syntax Notation One (ASN.1)",
International Standard 8824, December 1987.
[RFC3159] McCloghrie, K., Fine, M., Seligson, J., Chan, K., Hahn,
S., Sahita, R., Smith, A. and F. Reichmeyer, "Structure of
Policy Provisioning Information (SPPI)", RFC 3159, August
2001.
[IEEE754] Institute of Electrical and Electronics Engineers, "IEEE
Standard for Binary Floating-Point Arithmetic", ANSI/IEEE
Standard 754-1985, August 1985.
[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.
[RFC3416] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Version 2 of the Protocol Operations for the
Simple Network Management Protocol (SNMP)", STD 62, RFC
3416, December 2002.
Authors’ Addresses
Frank Strauss
TU Braunschweig
Muehlenpfordtstrasse 23
38106 Braunschweig
Germany
Phone: +49 531 391 3266
EMail: strauss@ibr.cs.tu-bs.de
URI: http://www.ibr.cs.tu-bs.de/
Juergen Schoenwaelder
International University Bremen
P.O. Box 750 561
28725 Bremen
Germany
Phone: +49 421 200 3587
EMail: j.schoenwaelder@iu-bremen.de
URI: http://www.eecs.iu-bremen.de/
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