Network Working Group Dave Thaler Internet-Draft Microsoft Expires: April 2000 21 October 1999 Subtree Retrieval MIB Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Expires April 2000 [Page 1] Draft GET-SUBTREE MIB October 1999 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. Expires April 2000 [Page 2] Draft GET-SUBTREE MIB October 1999 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 Expires April 2000 [Page 3] Draft GET-SUBTREE MIB October 1999 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. Expires April 2000 [Page 4] Draft GET-SUBTREE MIB October 1999 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 Expires April 2000 [Page 5] Draft GET-SUBTREE MIB October 1999 "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 Expires April 2000 [Page 6] Draft GET-SUBTREE MIB October 1999 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 Expires April 2000 [Page 7] Draft GET-SUBTREE MIB October 1999 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 Expires April 2000 [Page 8] Draft GET-SUBTREE MIB October 1999 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. Expires April 2000 [Page 9] Draft GET-SUBTREE MIB October 1999 [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, Expires April 2000 [Page 10] Draft GET-SUBTREE MIB October 1999 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. 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