Network Working Group K. McCloghrie

Network Working Group K. McCloghrie
Request for Comments: 2864 Cisco Systems
Category: Standards Track G. Hanson
ADC Telecommunications
June 2000

The Inverted Stack Table Extension to the Interfaces Group MIB

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Table of Contents

1 Introduction .................................................. 1
2 The SNMP Network Management Framework ......................... 1
3 Interface Sub-Layers and the ifStackTable ..................... 3
4 Definitions ................................................... 4
5 Acknowledgements .............................................. 7
6 References .................................................... 7
7 Security Considerations ....................................... 8
8 Authors' Addresses ............................................ 9
9 Notice on Intellectual Property ............................... 10
10 Full Copyright Statement ..................................... 11

1. Introduction

This memo defines a portion of the Management Information Base (MIB)
for use with network management protocols in the Internet community.
In particular, it describes managed objects which provide an inverted
mapping of the interface stack table used for managing network
interfaces.

2. The SNMP Network Management Framework

The SNMP Management Framework presently consists of five major
components:

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o An overall architecture, described in RFC 2571 [1].

o Mechanisms for describing and naming objects and events for the
purpose of management. The first version of this Structure of
Management Information (SMI) is called SMIv1 and described in STD
16, RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4]. The
second version, called SMIv2, is described in STD 58, which
consists of RFC 2578 [5], RFC 2579 [6] and RFC 2580 [7].

o Message protocols for transferring management information. The
first version of the SNMP message protocol is called SNMPv1 and
described in STD 15, RFC 1157 [8]. A second version of the SNMP
message protocol, which is not an Internet standards track
protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC
1906 [10]. The third version of the message protocol is called
SNMPv3 and described in RFC 1906 [10], RFC 2572 [11] and RFC 2574
[12].

o Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats is
described in STD 15, RFC 1157 [8]. A second set of protocol
operations and associated PDU formats is described in RFC 1905
[13].

o A set of fundamental applications described in RFC 2573 [14] and
the view-based access control mechanism described in RFC 2575
[15].

A more detailed introduction to the current SNMP Management Framework
can be found in RFC 2570 [18].

Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. Objects in the MIB are
defined using the mechanisms defined in the SMI.

This memo specifies a MIB module that is compliant to the SMIv2. A
MIB conforming to the SMIv1 can be produced through the appropriate
translations. The resulting translated MIB must be semantically
equivalent, except where objects or events are omitted because no
translation is possible (e.g., use of Counter64). Some machine
readable information in SMIv2 will be converted into textual
descriptions in SMIv1 during the translation process. However, this
loss of machine readable information is not considered to change the
semantics of the MIB.

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3. Interface Sub-Layers and the ifStackTable

MIB-II [16] defines objects for managing network interfaces by
providing a generic interface definition together with the ability to
define media-specific extensions. The generic objects are known as
the 'interfaces' group.

Experience in defining media-specific extensions showed the need to
distinguish between the multiple sub-layers beneath the
internetwork-layer. Consider, for example, an interface with PPP
running over an HDLC link which uses a RS232-like connector. Each of
these sub-layers has its own media-specific MIB module.

The latest definition of the 'interfaces' group in the IF-MIB [17]
satisfies this need by having each sub-layer be represented by its
own conceptual row in the ifTable. It also defines an additional MIB
table, the ifStackTable, to identify the "superior" and "subordinate"
sub-layers through ifIndex "pointers" to the appropriate conceptual
rows in the ifTable.

Each conceptual row in the ifStackTable represents a relationship
between two interfaces, where this relationship is that the "higher-
layer" interface runs "on top" of the "lower-layer" interface. For
example, if a PPP module operated directly over a serial interface,
the PPP module would be a "higher layer" to the serial interface, and
the serial interface would be a "lower layer" to the PPP module.
This concept of "higher-layer" and "lower-layer" is the same as
embodied in the definitions of the ifTable's packet counters.

The ifStackTable is INDEX-ed by the ifIndex values of the two
interfaces involved in the relationship. By necessity, one of these
ifIndex values must come first, and the IF-MIB chose to have the
higher-layer interface first, and the lower-layer interface second.
Due to this, it is straight-forward for a Network Management
application to read a subset of the ifStackTable and thereby
determine the interfaces which run underneath a particular interface.
However, to determine which interfaces run on top of a particular
interface, a Network Management application has no alternative but to
read the whole table. This is very inefficient when querying a
device which has many interfaces, and many conceptual rows in its
ifStackTable.

This MIB provides an inverted Interfaces Stack Table, the
ifInvStackTable. While it contains no additional information beyond
that already contained in the ifStackTable, the ifInvStackTable has
the ifIndex values in its INDEX clause in the reverse order, i.e.,
the lower-layer interface first, and the higher-layer interface
second. As a result, the ifInvStackTable is an inverted version of

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the same information contained in the ifStackTable. Thus, the
ifInvStackTable provides an efficient means for a Network Management
application to read a subset of the ifStackTable and thereby
determine which interfaces run on top of a particular interface.

4. Definitions

IF-INVERTED-STACK-MIB DEFINITIONS ::= BEGIN

IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, mib-2 FROM SNMPv2-SMI
RowStatus FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
ifStackGroup2,
ifStackHigherLayer, ifStackLowerLayer FROM IF-MIB;

ifInvertedStackMIB MODULE-IDENTITY
LAST-UPDATED "200006140000Z"
ORGANIZATION "IETF Interfaces MIB Working Group"
CONTACT-INFO
" Keith McCloghrie
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
US

408-526-5260
[email protected]"
DESCRIPTION
"The MIB module which provides the Inverted Stack Table for
interface sub-layers."
REVISION "200006140000Z"
DESCRIPTION
"Initial revision, published as RFC 2864"
::= { mib-2 77 }

ifInvMIBObjects OBJECT IDENTIFIER ::= { ifInvertedStackMIB 1 }

--
-- The Inverted Interface Stack Group
--

ifInvStackTable OBJECT-TYPE
SYNTAX SEQUENCE OF IfInvStackEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table containing information on the relationships between

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the multiple sub-layers of network interfaces. In
particular, it contains information on which sub-layers run
'underneath' which other sub-layers, where each sub-layer
corresponds to a conceptual row in the ifTable. For
example, when the sub-layer with ifIndex value x runs
underneath the sub-layer with ifIndex value y, then this
table contains:

ifInvStackStatus.x.y=active

For each ifIndex value, z, which identifies an active
interface, there are always at least two instantiated rows
in this table associated with z. For one of these rows, z
is the value of ifStackHigherLayer; for the other, z is the
value of ifStackLowerLayer. (If z is not involved in
multiplexing, then these are the only two rows associated
with z.)

For example, two rows exist even for an interface which has
no others stacked on top or below it:

ifInvStackStatus.z.0=active
ifInvStackStatus.0.z=active

This table contains exactly the same number of rows as the
ifStackTable, but the rows appear in a different order."
REFERENCE
"ifStackTable of RFC 2863"
::= { ifInvMIBObjects 1 }

ifInvStackEntry OBJECT-TYPE
SYNTAX IfInvStackEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Information on a particular relationship between two sub-
layers, specifying that one sub-layer runs underneath the
other sub-layer. Each sub-layer corresponds to a conceptual
row in the ifTable."
INDEX { ifStackLowerLayer, ifStackHigherLayer }
::= { ifInvStackTable 1 }

IfInvStackEntry ::=
SEQUENCE {
ifInvStackStatus RowStatus
}

ifInvStackStatus OBJECT-TYPE

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SYNTAX RowStatus
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The status of the relationship between two sub-layers.

An instance of this object exists for each instance of the
ifStackStatus object, and vice versa. For example, if the
variable ifStackStatus.H.L exists, then the variable
ifInvStackStatus.L.H must also exist, and vice versa. In
addition, the two variables always have the same value.

However, unlike ifStackStatus, the ifInvStackStatus object
is NOT write-able. A network management application wishing
to change a relationship between sub-layers H and L cannot
do so by modifying the value of ifInvStackStatus.L.H, but
must instead modify the value of ifStackStatus.H.L. After
the ifStackTable is modified, the change will be reflected
in this table."
::= { ifInvStackEntry 1 }

-- conformance information

ifInvConformance OBJECT IDENTIFIER ::= { ifInvMIBObjects 2 }

ifInvGroups OBJECT IDENTIFIER ::= { ifInvConformance 1 }
ifInvCompliances OBJECT IDENTIFIER ::= { ifInvConformance 2 }

-- compliance statements

ifInvCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP entities which provide
inverted information on the layering of network interfaces."

MODULE -- this module
MANDATORY-GROUPS { ifInvStackGroup }

OBJECT ifInvStackStatus
SYNTAX INTEGER { active(1) }
DESCRIPTION
"Support is only required for 'active'."

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MODULE IF-MIB
MANDATORY-GROUPS { ifStackGroup2 }

::= { ifInvCompliances 1 }

-- units of conformance

ifInvStackGroup OBJECT-GROUP
OBJECTS { ifInvStackStatus }
STATUS current
DESCRIPTION
"A collection of objects providing inverted information on
the layering of MIB-II interfaces."
::= { ifInvGroups 1 }

END

5. Acknowledgements

This memo has been produced by the IETF's Interfaces MIB working-
group.

6. References

[1] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
Describing SNMP Management Frameworks", RFC 2571, January 1998.

[2] Rose, M. and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16, RFC
1155, May 1990.

[3] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.

[4] Rose, M., "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.

[5] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

[6] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
RFC 2579, April 1999.

[7] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
58, RFC 2580, April 1999.

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[8] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.

[9] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901,
January 1996.

[10] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
Waldbusser, "Transport Mappings for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1906, January 1996.

[11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", RFC 2572, January 1998.

[12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
for version 3 of the Simple Network Management Protocol
(SNMPv3)", RFC 2574, January 1998.

[13] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Protocol Operations for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1905, January 1996.

[14] Levi, D., Meyer, P. and B. Stewart, "SNMP Applications", RFC
2573, January 1998.

[15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
Control Model (VACM) for the Simple Network Management Protocol
(SNMP)", RFC 2575, January 1998.

[16] McCloghrie, K. and M. Rose, "Management Information Base for
Network Management of TCP/IP-based internets - MIB-II", STD 17,
RFC 1213, March 1991.

[17] McCloghrie, K. and F. Kastenholz, "The Interface Group MIB", RFC
2863, June 2000.

[18] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction
to Version 3 of the Internet-standard Network Management
Framework", RFC 2570, April 1999.

7. Security Considerations

There are no management objects defined in this MIB that have a MAX-
ACCESS clause of read-write and/or read-create. So, if this MIB is
implemented correctly, then there is no risk that an intruder can
alter or create any management objects of this MIB via direct SNMP
SET operations.

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SNMPv1 by itself is not a secure environment. Even if the network
itself is secure (for example by using IPSec), even then, there is no
control as to who on the secure network is allowed to access and
GET/SET (read/change/create/delete) the objects in this MIB.

It is recommended that the implementers consider the security
features as provided by the SNMPv3 framework. Specifically, the use
of the User-based Security Model RFC 2574 [12] and the View- based
Access Control Model RFC 2575 [15] is recommended.

It is then a customer/user responsibility to ensure that the SNMP
entity giving access to an instance of this MIB, is properly
configured to give access to the objects only to those principals
(users) that have legitimate rights to indeed GET or SET
(change/create/delete) them.

8. Authors' Addresses

Keith McCloghrie
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706

Phone: 408-526-5260
EMail: [email protected]

Gary Hanson
ADC Telecommunications
14375 NW Science Park Drive
Portland, Oregon, 97229

Phone: (800)733-5511 x6333
EMail: [email protected]

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9. Notice on Intellectual Property

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

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10. Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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