Network Working Group Dave Thaler
Internet-Draft Microsoft
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Subtree Retrieval MIB
<draft-irtf-nmrg-get-subtree-mib-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
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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 used for
retrieving a subtree of MIB objects without the overshoot problems
of the SNMP GetBulkRequest operation.
2. The SNMP Network Management Framework
The SNMP Management Framework presently consists of five major
components:
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 RFC 1155 [2], RFC 1212 [3] and RFC 1215 [4]. The
second version, called SMIv2, is described in 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 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 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].
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.
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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 (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.
3. Overview
The GetBulkRequest operation in SNMP [13] aims to minimize the
number of protocol exchanges required to retrieve a large amount
of management information by returning a series of variable
bindings in a single response. The requester is required to
specify a "max-repetitions" count, and the agent then fills in as
many variable bindings as it can without exceeding either this
count, or the maximum message size.
One problem with retrieving tables with GetBulkRequest is that the
manager typically does not know the number of rows in the table,
and hence cannot set max-repetitions to the optimal value. As a
result, the manager must either set max-repetitions to some huge
value, resulting in a potentially large waste of bandwidth when
many more variable bindings are returned than are needed
(sometimes called "overshoot"), or else must issue multiple
GetBulkRequests sequentially to traverse a large table such as the
routing table in a backbone router.
This document describes a MIB than can be used by an application
to retrieve subtrees of information, without any change to the
SNMP protocol or SNMP protocol engines, as follows. The
application must have been pre-configured as a legal notification
target in the SNMP-TARGET-MIB [14].
The MIB described herein provides a table of outstanding
GetSubtree operations which allows row creation. To begin a
retrieval, an application issues a SetRequest to perform a row
creation in this table, which identifies the application
(represented by an entry in the snmpTargetAddrTable) as the
response destination. This row creation triggers the agent to
begin sending Traps containing the requested information to the
application. Each trap contains a sequence number object (which
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can be used to detect losses), and an flag object signalling
whether the trap is the final one in the sequence. Once all
information has been sent, the conceptual row is automatically
deleted.
Furthermore, if the request was in error (e.g., a human entered a
different OID from what was intended, causing the application to
receive large amounts of unwanted data), the MIB also provides a
way to halt an operation in progress, if the agent is able to
support this. Halting an operation in progress is accomplished
simply by allowing the application to delete the conceptual row
corresponding to the outstanding operation.
3.1. Limitations
The limitations of this approach that come with not changing SNMP
include:
o To use this MIB to retrieve subtrees of information, the
application must be able to issue SETs (at least to this
MIB), not just GETs.
o The command responder and notification originator need to be
tightly coupled, as well as the command generator and
notification responder.
o The subagent implementing this MIB must be able to call back
into the SNMP engine to walk other MIBs, without causing a
deadlock.
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4. Definitions
GET-SUBTREE-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, NOTIFICATION-TYPE,
Unsigned32, Counter32 FROM SNMPv2-SMI
RowStatus, TruthValue FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP,
NOTIFICATION-GROUP FROM SNMPv2-CONF
SnmpAdminString FROM SNMP-FRAMEWORK-MIB;
getSubtreeMIB MODULE-IDENTITY
LAST-UPDATED "9907161200Z"
ORGANIZATION "IRTF Network Management Research Group"
CONTACT-INFO
" Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
EMail: dthaler@dthaler.microsoft.com"
DESCRIPTION
"This MIB module provides the ability to retrieve an arbitary
subtree of OIDs by receiving traps."
::= { XXX }
getSubtreeMIBObjects OBJECT IDENTIFIER ::= { getSubtreeMIB 1 }
getSubtree OBJECT IDENTIFIER ::= { getSubtreeMIBObjects 1 }
getSubtreeTraps OBJECT IDENTIFIER ::= { getSubtreeMIBObjects 2 }
getSubtreeTable OBJECT-TYPE
SYNTAX SEQUENCE OF GetSubtreeEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table containing information on
GET-SUBTREE operations in progress."
::= { getSubtree 1 }
getSubtreeEntry OBJECT-TYPE
SYNTAX GetSubtreeEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
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"An entry (conceptual row) containing the information on a
particular GET-SUBTREE operation in progress."
INDEX { getSubtreeIndex }
::= { getSubtreeTable 1 }
GetSubtreeEntry ::= SEQUENCE {
getSubtreeIndex Unsigned32,
getSubtreeTargetAddrName SnmpAdminString,
getSubtreeRootOid OBJECT IDENTIFIER,
getSubtreeSequenceNumber Counter32,
getSubtreeDone TruthValue,
getSubtreeStatus RowStatus
}
getSubtreeIndex OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An integer uniquely identifying the GET-SUBTREE operation in
progress. This value should be randomly generated by a
manager before attempting to create the row."
::= { getSubtreeEntry 1 }
getSubtreeTargetAddrName OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object selects a management target defined in the
snmpTargetAddrTable (in the SNMP-TARGET-MIB). The
selected target is defined by an entry in the
snmpTargetAddrTable whose index value (snmpTargetAddrName)
is equal to this object."
::= { getSubtreeEntry 2 }
getSubtreeRootOid OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The OID of the subtree to be sent."
::= { getSubtreeEntry 3 }
getSubtreeSequenceNumber OBJECT-TYPE
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SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of trap responses previously sent for this request."
::= { getSubtreeEntry 4 }
getSubtreeDone OBJECT-TYPE
SYNTAX TruthValue
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This is set to true in the last trap sent, and is set to
false otherwise."
::= { getSubtreeEntry 5 }
getSubtreeStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this row, by which new entries may be
created, or old entries deleted from this table. Once
created, the row may be deleted, but other objects in the
row may not be modified. A row will be deleted automatically
by the agent once the operation has completed.
Creating a row will cause the subtree retrieval operation
to commence. If the agent allows aborting operations in
progress, deleting a row will cause the operation to halt."
::= { getSubtreeEntry 6 }
-- traps
getSubtreeTrapPrefix OBJECT IDENTIFIER ::= { getSubtreeTraps 0 }
getSubtreeResponse NOTIFICATION-TYPE
OBJECTS { getSubtreeSequenceNumber, getSubtreeDone }
STATUS current
DESCRIPTION
"In addition to the two objects above, this trap also
contains a series of varbinds containing the next chunk of
the subtree. The generating entity will append, in order,
as many variables to the variable-bindings field as it can
without exceeding the maximum message size, and without going
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beyond the subtree of OIDs requested. A series of such
traps will be generated until the end of the subtree is
reached."
::= { getSubtreeTrapPrefix 1 }
-- conformance information
getSubtreeMIBConformance
OBJECT IDENTIFIER ::= { getSubtreeMIB 2 }
getSubtreeMIBCompliances
OBJECT IDENTIFIER ::= { getSubtreeMIBConformance 1 }
getSubtreeMIBGroups OBJECT IDENTIFIER ::= { getSubtreeMIBConformance 2 }
-- compliance statements
getSubtreeMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for the GetSubtree MIB."
MODULE -- this module
MANDATORY-GROUPS { getSubtreeObjectGroup,
getSubtreeNotificationGroup }
::= { getSubtreeMIBCompliances 1 }
-- units of conformance
getSubtreeObjectGroup OBJECT-GROUP
OBJECTS { getSubtreeTargetAddrName, getSubtreeRootOid,
getSubtreeSequenceNumber, getSubtreeDone,
getSubtreeStatus }
STATUS current
DESCRIPTION
"A collection of objects to support requests for
subtree retrieval operations."
::= { getSubtreeMIBGroups 1 }
getSubtreeNotificationGroup NOTIFICATION-GROUP
NOTIFICATIONS { getSubtreeResponse }
STATUS current
DESCRIPTION
"The notification which an entity is required to implement."
::= { getSubtreeMIBGroups 2 }
END
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5. Security Considerations
While unauthorized read access to the objects in this MIB is
relatively innocuous, unauthorized write access could trigger
sending of a potentially large amount of data to an authorized
notification receiver, which could be viewed as a denial-of-
service attack.
Hence, the support for SNMP operations in a non-secure environment
without proper protection can have a negative effect on network
operations.
SNMPv1 by itself is such an insecure environment. Even if the
network itself is secure (for example by using IPSec [16]), even
then, there is no control as to who on the secure network is
allowed to access and SET (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 2274 [12] and the View-
based Access Control Model RFC 2275 [15] is recommended.
It is then a customer/user responsibility to ensure that the SNMP
entity giving access to this MIB, is properly configured to give
access to those objects only to those principals (users) that have
legitimate rights to access them.
6. Authors' Addresses
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
7. References
[1] Wijnen, B., Harrington, D., and R. Presuhn, "An Architecture
for Describing SNMP Management Frameworks", RFC 2571,
Cabletron Systems, Inc., BMC Software, Inc., IBM T. J. Watson
Research, April 1999.
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[2] Rose, M., and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16,
RFC 1155, Performance Systems International, Hughes LAN
Systems, May 1990.
[3] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD
16, RFC 1212, Performance Systems International, Hughes LAN
Systems, March 1991.
[4] M. Rose, "A Convention for Defining Traps for use with the
SNMP", RFC 1215, Performance Systems International, March
1991.
[5] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Structure
of Management Information Version 2 (SMIv2)", STD 58, RFC
2578, April 1999.
[6] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Textual
Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[7] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580, April
1999.
[8] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, SNMP
Research, Performance Systems International, Performance
Systems International, MIT Laboratory for Computer Science,
May 1990.
[9] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901, SNMP
Research, Inc., Cisco Systems, Inc., Dover Beach Consulting,
Inc., International Network Services, January 1996.
[10] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Transport Mappings for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1906, SNMP Research, Inc.,
Cisco Systems, Inc., Dover Beach Consulting, Inc.,
International Network Services, 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, SNMP Research, Inc., Cabletron
Systems, Inc., BMC Software, Inc., IBM T. J. Watson Research,
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April 1999.
[12] Blumenthal, U., and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management Protocol
(SNMPv3)", RFC 2574, IBM T. J. Watson Research, April 1999.
[13] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1905, SNMP Research, Inc.,
Cisco Systems, Inc., Dover Beach Consulting, Inc.,
International Network Services, January 1996.
[14] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications",
RFC 2573, SNMP Research, Inc., Secure Computing Corporation,
Cisco Systems, April 1999.
[15] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network Management
Protocol (SNMP)", RFC 2575, IBM T. J. Watson Research, BMC
Software, Inc., Cisco Systems, Inc., April 1999.
8. Full Copyright Statement
Copyright (C) The Internet Society (1999). 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 implmentation 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
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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.
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