Network Working Group M. Rose Request for Comments: 1212 Performance Systems International K. McCloghrie Hughes LAN Systems Editors March 1991
Concise MIB Definitions Status of this Memo
This memo defines a format for producing MIB modules. This RFC specifies an IAB standards track document for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Table of Contents
1. Abstract.............................................. 2 2. Historical Perspective ............................... 2 3. Columnar Objects ..................................... 3 3.1 Row Deletion ........................................ 4 3.2 Row Addition ........................................ 4 4. Defining Objects ..................................... 5 4.1 Mapping of the OBJECT-TYPE macro .................... 7 4.1.1 Mapping of the SYNTAX clause ...................... 7 4.1.2 Mapping of the ACCESS clause ...................... 8 4.1.3 Mapping of the STATUS clause ...................... 8 4.1.4 Mapping of the DESCRIPTION clause ................. 8 4.1.5 Mapping of the REFERENCE clause ................... 8 4.1.6 Mapping of the INDEX clause ....................... 8 4.1.7 Mapping of the DEFVAL clause ...................... 10 4.1.8 Mapping of the OBJECT-TYPE value .................. 11 4.2 Usage Example ....................................... 11 5. Appendix: DE-osifying MIBs ........................... 13 5.1 Managed Object Mapping .............................. 14 5.1.1 Mapping to the SYNTAX clause ...................... 15 5.1.2 Mapping to the ACCESS clause ...................... 15 5.1.3 Mapping to the STATUS clause ...................... 15 5.1.4 Mapping to the DESCRIPTION clause ................. 15 5.1.5 Mapping to the REFERENCE clause ................... 16 5.1.6 Mapping to the INDEX clause ....................... 16 5.1.7 Mapping to the DEFVAL clause ...................... 16 5.2 Action Mapping ...................................... 16 5.2.1 Mapping to the SYNTAX clause ...................... 16 5.2.2 Mapping to the ACCESS clause ...................... 16
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5.2.3 Mapping to the STATUS clause ...................... 16 5.2.4 Mapping to the DESCRIPTION clause ................. 16 5.2.5 Mapping to the REFERENCE clause ................... 16 6. Acknowledgements ..................................... 17 7. References ........................................... 18 8. Security Considerations............................... 19 9. Authors' Addresses.................................... 19
1. Abstract
This memo describes a straight-forward approach toward producing concise, yet descriptive, MIB modules. It is intended that all future MIB modules be written in this format.
2. Historical Perspective
As reported in RFC 1052, IAB Recommendations for the Development of Internet Network Management Standards [1], a two-prong strategy for network management of TCP/IP-based internets was undertaken. In the short-term, the Simple Network Management Protocol (SNMP), defined in RFC 1067, was to be used to manage nodes in the Internet community. In the long-term, the use of the OSI network management framework was to be examined. Two documents were produced to define the management information: RFC 1065, which defined the Structure of Management Information (SMI), and RFC 1066, which defined the Management Information Base (MIB). Both of these documents were designed so as to be compatible with both the SNMP and the OSI network management framework.
This strategy was quite successful in the short-term: Internet-based network management technology was fielded, by both the research and commercial communities, within a few months. As a result of this, portions of the Internet community became network manageable in a timely fashion.
As reported in RFC 1109, Report of the Second Ad Hoc Network Management Review Group [2], the requirements of the SNMP and the OSI network management frameworks were more different than anticipated. As such, the requirement for compatibility between the SMI/MIB and both frameworks was suspended. This action permitted the operational network management framework, based on the SNMP, to respond to new operational needs in the Internet community by producing MIB-II.
In May of 1990, the core documents were elevated to "Standard Protocols" with "Recommended" status. As such, the Internet-standard network management framework consists of: Structure and Identification of Management Information for TCP/IP-based internets, RFC 1155 [3], which describes how managed objects contained in the
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MIB are defined; Management Information Base for Network Management of TCP/IP-based internets, which describes the managed objects contained in the MIB, RFC 1156 [4]; and, the Simple Network Management Protocol, RFC 1157 [5], which defines the protocol used to manage these objects. Consistent with the IAB directive to produce simple, workable systems in the short-term, the list of managed objects defined in the Internet-standard MIB was derived by taking only those elements which are considered essential. However, the SMI defined three extensibility mechanisms: one, the addition of new standard objects through the definitions of new versions of the MIB; two, the addition of widely-available but non-standard objects through the experimental subtree; and three, the addition of private objects through the enterprises subtree. Such additional objects can not only be used for vendor-specific elements, but also for experimentation as required to further the knowledge of which other objects are essential.
As more objects are defined using the second method, experience has shown that the resulting MIB descriptions contain redundant information. In order to provide for MIB descriptions which are more concise, and yet as informative, an enhancement is suggested. This enhancement allows the author of a MIB to remove the redundant information, while retaining the important descriptive text.
Before presenting the approach, a brief presentation of columnar object handling by the SNMP is necessary. This explains and further motivates the value of the enhancement.
3. Columnar Objects
The SNMP supports operations on MIB objects whose syntax is ObjectSyntax as defined in the SMI. Informally stated, SNMP operations apply exclusively to scalar objects. However, it is convenient for developers of management applications to impose imaginary, tabular structures on the ordered collection of objects that constitute the MIB. Each such conceptual table contains zero or more rows, and each row may contain one or more scalar objects, termed columnar objects. Historically, this conceptualization has been formalized by using the OBJECT-TYPE macro to define both an object which corresponds to a table and an object which corresponds to a row in that table. (The ACCESS clause for such objects is "not-accessible", of course.) However, it must be emphasized that, at the protocol level, relationships among columnar objects in the same row is a matter of convention, not of protocol.
Note that there are good reasons why the tabular structure is not a matter of protocol. Consider the operation of the SNMP Get-Next-PDU acting on the last columnar object of an instance of a conceptual
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row; it returns the next column of the first conceptual row or the first object instance occurring after the table. In contrast, if the rows were a matter of protocol, then it would instead return an error. By not returning an error, a single PDU exchange informs the manager that not only has the end of the conceptual row/table been reached, but also provides information on the next object instance, thereby increasing the information density of the PDU exchange.
3.1. Row Deletion
Nonetheless, it is highly useful to provide a means whereby a conceptual row may be removed from a table. In MIB-II, this was achieved by defining, for each conceptual row, an integer-valued columnar object. If a management station sets the value of this object to some value, usually termed "invalid", then the effect is one of invalidating the corresponding row in the table. However, it is an implementation-specific matter as to whether an agent removes an invalidated entry from the table. Accordingly, management stations must be prepared to receive tabular information from agents that corresponds to entries not currently in use. Proper interpretation of such entries requires examination of the columnar object indicating the in-use status.
3.2. Row Addition
It is also highly useful to have a clear understanding of how a conceptual row may be added to a table. In the SNMP, at the protocol level, a management station issues an SNMP set operation containing an arbitrary set of variable bindings. In the case that an agent detects that one or more of those variable bindings refers to an object instance not currently available in that agent, it may, according to the rules of the SNMP, behave according to any of the following paradigms:
(1) It may reject the SNMP set operation as referring to non-existent object instances by returning a response with the error-status field set to "noSuchName" and the error-index field set to refer to the first vacuous reference.
(2) It may accept the SNMP set operation as requesting the creation of new object instances corresponding to each of the object instances named in the variable bindings. The value of each (potentially) newly created object instance is specified by the "value" component of the relevant variable binding. In this case, if the request specifies a value for a newly (or previously) created object that it deems inappropriate by reason of value or
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syntax, then it rejects the SNMP set operation by responding with the error-status field set to badValue and the error-index field set to refer to the first offending variable binding.
(3) It may accept the SNMP set operation and create new object instances as described in (2) above and, in addition, at its discretion, create supplemental object instances to complete a row in a conceptual table of which the new object instances specified in the request may be a part.
It should be emphasized that all three of the above behaviors are fully conformant to the SNMP specification and are fully acceptable, subject to any restrictions which may be imposed by access control and/or the definitions of the MIB objects themselves.
4. Defining Objects
The Internet-standard SMI employs a two-level approach towards object definition. A MIB definition consists of two parts: a textual part, in which objects are placed into groups, and a MIB module, in which objects are described solely in terms of the ASN.1 macro OBJECT-TYPE, which is defined by the SMI.
An example of the former definition might be:
OBJECT: ------- sysLocation { system 6 }
Syntax: DisplayString (SIZE (0..255))
Definition: The physical location of this node (e.g., "telephone closet, 3rd floor").
ACCESS read-only STATUS mandatory ::= { system 6 }
In the interests of brevity and to reduce the chance of editing errors, it would seem useful to combine the two definitions. This can be accomplished by defining an extension to the OBJECT-TYPE macro:
IMPORTS ObjectName FROM RFC1155-SMI DisplayString FROM RFC1158-MIB;
OBJECT-TYPE MACRO ::= BEGIN TYPE NOTATION ::= -- must conform to -- RFC1155's ObjectSyntax "SYNTAX" type(ObjectSyntax) "ACCESS" Access "STATUS" Status DescrPart ReferPart IndexPart DefValPart VALUE NOTATION ::= value (VALUE ObjectName)
DescrPart ::= "DESCRIPTION" value (description DisplayString) | empty
ReferPart ::= "REFERENCE" value (reference DisplayString) | empty
IndexPart ::= "INDEX" "{" IndexTypes "}"
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| empty IndexTypes ::= IndexType | IndexTypes "," IndexType IndexType ::= -- if indexobject, use the SYNTAX -- value of the correspondent -- OBJECT-TYPE invocation value (indexobject ObjectName) -- otherwise use named SMI type -- must conform to IndexSyntax below | type (indextype)
DefValPart ::= "DEFVAL" "{" value (defvalue ObjectSyntax) "}" | empty
It should be noted that the expansion of the OBJECT-TYPE macro is something which conceptually happens during implementation and not during run-time.
4.1.1. Mapping of the SYNTAX clause
The SYNTAX clause, which must be present, defines the abstract data structure corresponding to that object type. The ASN.1 language [6] is used for this purpose. However, the SMI purposely restricts the ASN.1 constructs which may be used. These restrictions are made expressly for simplicity.
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4.1.2. Mapping of the ACCESS clause
The ACCESS clause, which must be present, defines the minimum level of support required for that object type. As a local matter, implementations may support other access types (e.g., an implementation may elect to permitting writing a variable marked as read-only). Further, protocol-specific "views" (e.g., those indirectly implied by an SNMP community) may make further restrictions on access to a variable.
4.1.3. Mapping of the STATUS clause
The STATUS clause, which must be present, defines the implementation support required for that object type.
4.1.4. Mapping of the DESCRIPTION clause
The DESCRIPTION clause, which need not be present, contains a textual definition of that object type which provides all semantic definitions necessary for implementation, and should embody any information which would otherwise be communicated in any ASN.1 commentary annotations associated with the object. Note that, in order to conform to the ASN.1 syntax, the entire value of this clause must be enclosed in double quotation marks, although the value may be multi-line.
Further, note that if the MIB module does not contain a textual description of the object type elsewhere then the DESCRIPTION clause must be present.
4.1.5. Mapping of the REFERENCE clause
The REFERENCE clause, which need not be present, contains a textual cross-reference to an object defined in some other MIB module. This is useful when de-osifying a MIB produced by some other organization.
4.1.6. Mapping of the INDEX clause
The INDEX clause, which may be present only if that object type corresponds to a conceptual row, defines instance identification information for that object type. (Historically, each MIB definition contained a section entitled "Identification of OBJECT instances for use with the SNMP". By using the INDEX clause, this section need no longer occur as this clause concisely captures the precise semantics needed for instance identification.)
If the INDEX clause is not present, and the object type corresponds to a non-columnar object, then instances of the object are identified
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by appending a sub-identifier of zero to the name of that object. Further, note that if the MIB module does not contain a textual description of how instance identification information is derived for columnar objects, then the INDEX clause must be present.
To define the instance identification information, determine which object value(s) will unambiguously distinguish a conceptual row. The syntax of those objects indicate how to form the instance-identifier:
(1) integer-valued: a single sub-identifier taking the integer value (this works only for non-negative integers);
(2) string-valued, fixed-length strings: `n' sub-identifiers, where `n' is the length of the string (each octet of the string is encoded in a separate sub-identifier);
(3) string-valued, variable-length strings: `n+1' sub- identifiers, where `n' is the length of the string (the first sub-identifier is `n' itself, following this, each octet of the string is encoded in a separate sub- identifier);
(4) object identifier-valued: `n+1' sub-identifiers, where `n' is the number of sub-identifiers in the value (the first sub-identifier is `n' itself, following this, each sub-identifier in the value is copied);
(5) NetworkAddress-valued: `n+1' sub-identifiers, where `n' depends on the kind of address being encoded (the first sub-identifier indicates the kind of address, value 1 indicates an IpAddress); or,
(6) IpAddress-valued: 4 sub-identifiers, in the familiar a.b.c.d notation.
Note that if an "indextype" value is present (e.g., INTEGER rather than ifIndex), then a DESCRIPTION clause must be present; the text contained therein indicates the semantics of the "indextype" value.
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By way of example, in the context of MIB-II [7], the following INDEX clauses might be present:
The DEFVAL clause, which need not be present, defines an acceptable default value which may be used when an object instance is created at the discretion of the agent acting in conformance with the third paradigm described in Section 4.2 above.
During conceptual row creation, if an instance of a columnar object is not present as one of the operands in the correspondent SNMP set operation, then the value of the DEFVAL clause, if present, indicates an acceptable default value that the agent might use.
The value of the DEFVAL clause must, of course, correspond to the SYNTAX clause for the object. Note that if an operand to the SNMP set operation is an instance of a read-only object, then the error noSuchName will be returned. As such, the DEFVAL clause can be used to provide an acceptable default value that the agent might use.
It is possible that no acceptable default value may exist for any of the columnar objects in a conceptual row for which the creation of new object instances is allowed. In this case, the objects specified in the INDEX clause must have a corresponding ACCESS clause value of read-write.
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By way of example, consider the following possible DEFVAL clauses:
The value of an invocation of the OBJECT-TYPE macro is the name of the object, which is an object identifier.
4.2. Usage Example
Consider how the ipNetToMediaTable from MIB-II might be fully described:
-- the IP Address Translation tables
-- The Address Translation tables contain IpAddress to -- "physical" address equivalences. Some interfaces do not -- use translation tables for determining address equivalences -- (e.g., DDN-X.25 has an algorithmic method); if all -- interfaces are of this type, then the Address Translation -- table is empty, i.e., has zero entries.
ipNetToMediaTable OBJECT-TYPE SYNTAX SEQUENCE OF IpNetToMediaEntry ACCESS not-accessible STATUS mandatory DESCRIPTION "The IP Address Translation table used for mapping from IP addresses to physical addresses." ::= { ip 22 }
ipNetToMediaEntry OBJECT-TYPE SYNTAX IpNetToMediaEntry ACCESS not-accessible STATUS mandatory DESCRIPTION "Each entry contains one IpAddress to 'physical'
ipNetToMediaIfIndex OBJECT-TYPE SYNTAX INTEGER ACCESS read-write STATUS mandatory DESCRIPTION "The interface on which this entry's equivalence is effective. The interface identified by a particular value of this index is the same interface as identified by the same value of ifIndex." ::= { ipNetToMediaEntry 1 }
ipNetToMediaPhysAddress OBJECT-TYPE SYNTAX OCTET STRING ACCESS read-write STATUS mandatory DESCRIPTION "The media-dependent 'physical' address." ::= { ipNetToMediaEntry 2 }
ipNetToMediaNetAddress OBJECT-TYPE SYNTAX IpAddress ACCESS read-write STATUS mandatory DESCRIPTION "The IpAddress corresponding to the media- dependent 'physical' address." ::= { ipNetToMediaEntry 3 }
ipNetToMediaType OBJECT-TYPE SYNTAX INTEGER {
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other(1), -- none of the following invalid(2), -- an invalidated mapping dynamic(3), static(4) } ACCESS read-write STATUS mandatory DESCRIPTION "The type of mapping.
Setting this object to the value invalid(2) has the effect of invalidating the corresponding entry in the ipNetToMediaTable. That is, it effectively disassociates the interface identified with said entry from the mapping identified with said entry. It is an implementation-specific matter as to whether the agent removes an invalidated entry from the table. Accordingly, management stations must be prepared to receive tabular information from agents that corresponds to entries not currently in use. Proper interpretation of such entries requires examination of the relevant ipNetToMediaType object." ::= { ipNetToMediaEntry 4 }
5. Appendix: DE-osifying MIBs
There has been an increasing amount of work recently on taking MIBs defined by other organizations (e.g., the IEEE) and de-osifying them for use with the Internet-standard network management framework. The steps to achieve this are straight-forward, though tedious. Of course, it is helpful to already be experienced in writing MIB modules for use with the Internet-standard network management framework.
The first step is to construct a skeletal MIB module, e.g.,
RFC1213-MIB DEFINITIONS ::= BEGIN
IMPORTS experimental, OBJECT-TYPE, Counter FROM RFC1155-SMI;
-- contact IANA for actual number root OBJECT IDENTIFIER ::= { experimental xx }
END
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The next step is to categorize the objects into groups. For experimental MIBs, optional objects are permitted. However, when a MIB module is placed in the Internet-standard space, these optional objects are either removed, or placed in a optional group, which, if implemented, all objects in the group must be implemented. For the first pass, it is wisest to simply ignore any optional objects in the original MIB: experience shows it is better to define a core MIB module first, containing only essential objects; later, if experience demands, other objects can be added.
It must be emphasized that groups are "units of conformance" within a MIB: everything in a group is "mandatory" and implementations do either whole groups or none.
5.1. Managed Object Mapping
Next for each managed object class, determine whether there can exist multiple instances of that managed object class. If not, then for each of its attributes, use the OBJECT-TYPE macro to make an equivalent definition.
Otherwise, if multiple instances of the managed object class can exist, then define a conceptual table having conceptual rows each containing a columnar object for each of the managed object class's attributes. If the managed object class is contained within the containment tree of another managed object class, then the assignment of an object type is normally required for each of the "distinguished attributes" of the containing managed object class. If they do not already exist within the MIB module, then they can be added via the definition of additional columnar objects in the conceptual row corresponding to the contained managed object class.
In defining a conceptual row, it is useful to consider the optimization of network management operations which will act upon its columnar objects. In particular, it is wisest to avoid defining more columnar objects within a conceptual row, than can fit in a single PDU. As a rule of thumb, a conceptual row should contain no more than approximately 20 objects. Similarly, or as a way to abide by the "20 object guideline", columnar objects should be grouped into tables according to the expected grouping of network management operations upon them. As such, the content of conceptual rows should reflect typical access scenarios, e.g., they should be organized along functional lines such as one row for statistics and another row for parameters, or along usage lines such as commonly-needed objects versus rarely-needed objects.
On the other hand, the definition of conceptual rows where the number of columnar objects used as indexes outnumbers the number used to
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hold information, should also be avoided. In particular, the splitting of a managed object class's attributes into many conceptual tables should not be used as a way to obtain the same degree of flexibility/complexity as is often found in MIB's with a myriad of optionals.
5.1.1. Mapping to the SYNTAX clause
When mapping to the SYNTAX clause of the OBJECT-type macro:
(1) An object with BOOLEAN syntax becomes an INTEGER taking either of values true(1) or false(2).
(2) An object with ENUMERATED syntax becomes an INTEGER, taking any of the values given.
(3) An object with BIT STRING syntax containing no more than 32 bits becomes an INTEGER defined as a sum; otherwise if more than 32 bits are present, the object becomes an OCTET STRING, with the bits numbered from left-to-right, in which the least significant bits of the last octet may be "reserved for future use".
(4) An object with a character string syntax becomes either an OCTET STRING or a DisplayString, depending on the repertoire of the character string.
(5) An non-tabular object with a complex syntax, such as REAL or EXTERNAL, must be decomposed, usually into an OCTET STRING (if sensible). As a rule, any object with a complicated syntax should be avoided.
(6) Tabular objects must be decomposed into rows of columnar objects.
5.1.2. Mapping to the ACCESS clause
This is straight-forward.
5.1.3. Mapping to the STATUS clause
This is usually straight-forward; however, some osified-MIBs use the term "recommended". In this case, a choice must be made between "mandatory" and "optional".
5.1.4. Mapping to the DESCRIPTION clause
This is straight-forward: simply copy the text, making sure that any
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embedded double quotation marks are sanitized (i.e., replaced with single-quotes or removed).
5.1.5. Mapping to the REFERENCE clause
This is straight-forward: simply include a textual reference to the object being mapped, the document which defines the object, and perhaps a page number in the document.
5.1.6. Mapping to the INDEX clause
Decide how instance-identifiers for columnar objects are to be formed and define this clause accordingly.
5.1.7. Mapping to the DEFVAL clause
Decide if a meaningful default value can be assigned to the object being mapped, and if so, define the DEFVAL clause accordingly.
5.2. Action Mapping
Actions are modeled as read-write objects, in which writing a particular value results in the action taking place.
5.2.1. Mapping to the SYNTAX clause
Usually an INTEGER syntax is used with a distinguished value provided for each action that the object provides access to. In addition, there is usually one other distinguished value, which is the one returned when the object is read.
5.2.2. Mapping to the ACCESS clause
Always use read-write.
5.2.3. Mapping to the STATUS clause
This is straight-forward.
5.2.4. Mapping to the DESCRIPTION clause
This is straight-forward: simply copy the text, making sure that any embedded double quotation marks are sanitized (i.e., replaced with single-quotes or removed).
5.2.5. Mapping to the REFERENCE clause
This is straight-forward: simply include a textual reference to the
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action being mapped, the document which defines the action, and perhaps a page number in the document.
6. Acknowledgements
This document was produced by the SNMP Working Group:
Anne Ambler, Spider Karl Auerbach, Sun Fred Baker, ACC Ken Brinkerhoff Ron Broersma, NOSC Jack Brown, US Army Theodore Brunner, Bellcore Jeffrey Buffum, HP John Burress, Wellfleet Jeffrey D. Case, University of Tennessee at Knoxville Chris Chiptasso, Spartacus Paul Ciarfella, DEC Bob Collet John Cook, Chipcom Tracy Cox, Bellcore James R. Davin, MIT-LCS Eric Decker, cisco Kurt Dobbins, Cabletron Nadya El-Afandi, Network Systems Gary Ellis, HP Fred Engle Mike Erlinger Mark S. Fedor, PSI Richard Fox, Synoptics Karen Frisa, CMU Chris Gunner, DEC Fred Harris, University of Tennessee at Knoxville Ken Hibbard, Xylogics Ole Jacobsen, Interop Ken Jones Satish Joshi, Synoptics Frank Kastenholz, Racal-Interlan Shimshon Kaufman, Spartacus Ken Key, University of Tennessee at Knoxville Jim Kinder, Fibercom Alex Koifman, BBN Christopher Kolb, PSI Cheryl Krupczak, NCR Paul Langille, DEC Peter Lin, Vitalink John Lunny, TWG
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Carl Malamud Randy Mayhew, University of Tennessee at Knoxville Keith McCloghrie, Hughes LAN Systems Donna McMaster, David Systems Lynn Monsanto, Sun Dave Perkins, 3COM Jim Reinstedler, Ungerman Bass Anil Rijsinghani, DEC Kathy Rinehart, Arnold AFB Kary Robertson Marshall T. Rose, PSI (chair) L. Michael Sabo, NCSC Jon Saperia, DEC Greg Satz, cisco Martin Schoffstall, PSI John Seligson Steve Sherry, Xyplex Fei Shu, NEC Sam Sjogren, TGV Mark Sleeper, Sparta Lance Sprung Mike St.Johns Bob Stewart, Xyplex Emil Sturniold Kaj Tesink, Bellcore Dean Throop, Data General Bill Townsend, Xylogics Maurice Turcotte, Racal-Milgo Kannan Varadhou Sudhanshu Verma, HP Bill Versteeg, Network Research Corporation Warren Vik, Interactive Systems David Waitzman, BBN Steve Waldbusser, CMU Dan Wintringhan David Wood Wengyik Yeong, PSI Jeff Young, Cray Research
7. References
[1] Cerf, V., "IAB Recommendations for the Development of Internet Network Management Standards", RFC 1052, NRI, April 1988.
[2] Cerf, V., "Report of the Second Ad Hoc Network Management Review Group", RFC 1109, NRI, August 1989.
[3] Rose M., and K. McCloghrie, "Structure and Identification of
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Management Information for TCP/IP-based internets", RFC 1155, Performance Systems International, Hughes LAN Systems, May 1990.
[4] McCloghrie K., and M. Rose, "Management Information Base for Network Management of TCP/IP-based internets", RFC 1156, Hughes LAN Systems, Performance Systems International, May 1990.
[5] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network Management Protocol", RFC 1157, SNMP Research, Performance Systems International, Performance Systems International, MIT Laboratory for Computer Science, May 1990.
[6] Information processing systems - Open Systems Interconnection - Specification of Abstract Syntax Notation One (ASN.1), International Organization for Standardization International Standard 8824, December 1987.
[7] Rose M., Editor, "Management Information Base for Network Management of TCP/IP-based internets: MIB-II", RFC 1213, Performance Systems International, March 1991.
8. Security Considerations
Security issues are not discussed in this memo.
9. Authors' Addresses
Marshall T. Rose Performance Systems International 5201 Great America Parkway Suite 3106 Santa Clara, CA 95054
