RFC 3165
Definitions of Managed Objects for the Delegation of Management Scripts
Network Working Group D. Levi Request for Comments: 3165 Nortel Networks Obsoletes: 2592 J. Schoenwaelder Category: Standards Track TU Braunschweig August 2001 Definitions of Managed Objects for the Delegation of Management Scripts 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 (2001). All Rights Reserved.Abstract
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 a set of managed objects that allow the delegation of management scripts to distributed managers.
Table of Contents
1 Introduction ................................................. 3 2 The SNMP Management Framework ................................ 3 3 Overview ..................................................... 4 3.1 Terms ...................................................... 5 4 Requirements and Design Issues ............................... 6 4.1 Script Languages ........................................... 6 4.2 Script Transfer ............................................ 7 4.3 Script Execution ........................................... 8 5 Structure of the MIB ......................................... 9 5.1 Language Group ............................................. 9 5.2 Script Group ............................................... 10 5.3 Code Group ................................................. 11 5.4 Launch Group ............................................... 11 5.5 Run Group .................................................. 11 6 Definitions .................................................. 12 7 Usage Examples ............................................... 49 7.1 Pushing a Script via SNMP .................................. 49 7.2 Pulling a Script from a URL ................................ 50 7.3 Modifying an Existing Script ............................... 50 7.4 Removing an Existing Script ................................ 51 7.5 Creating a Launch Button ................................... 51 7.6 Launching a Script ......................................... 52 7.7 Suspending a Running Script ................................ 52 7.8 Resuming a Suspended Script ................................ 53 7.9 Terminating a Running Script ............................... 53 7.10 Removing a Terminated Script .............................. 54 7.11 Removing a Launch Button .................................. 54 8 VACM Configuration Examples .................................. 54 8.1 Sandbox for Guests ......................................... 55 8.2 Sharing Scripts ............................................ 55 8.3 Emergency Scripts .......................................... 56 9 IANA Considerations .......................................... 57 10 Security Considerations ..................................... 57 11 Intellectual Property ....................................... 59 12 Changes from RFC 2592 ....................................... 59 13 Acknowledgments ............................................. 61 14 References .................................................. 61 15 Editors' Addresses .......................................... 63 16 Full Copyright Statement .................................... 64
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 a set of managed objects that allow the delegation of management scripts to distributed managers. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].2. The SNMP Management Framework
The SNMP Management Framework presently consists of five major components: o An overall architecture, described in RFC 2571 [RFC2571]. 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 [RFC1155], STD 16, RFC 1212 [RFC1212] and RFC 1215 [RFC1215]. The second version, called SMIv2, is described in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580 [RFC2580]. 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 [RFC1157]. A second version of the SNMP message protocol, which is not an Internet standards track protocol, is called SNMPv2c and described in RFC 1901 [RFC1901] and RFC 1906 [RFC1906]. The third version of the message protocol is called SNMPv3 and described in RFC 1906 [RFC1906], RFC 2572 [RFC2572] and RFC 2574 [RFC2574]. o Protocol operations for accessing management information. The first set of protocol operations and associated PDU formats is described in STD 15, RFC 1157 [RFC1157]. A second set of protocol operations and associated PDU formats is described in RFC 1905 [RFC1905]. o A set of fundamental applications described in RFC 2573 [RFC2573] and the view-based access control mechanism described in RFC 2575 [RFC2575]. A more detailed introduction to the current SNMP Management Framework can be found in RFC 2570 [RFC2570].
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 (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 Script MIB module defined in this memo can be used to delegate management functions to distributed managers. Management functions are defined as management scripts written in a management scripting language. This MIB makes no assumptions about the language itself and even allows distribution of compiled native code, if an implementation is able to execute native code under the control of this MIB. The Script MIB defines a standard interface for the delegation of management functions based on the Internet management framework. In particular, it provides the following capabilities: 1. Capabilities to transfer management scripts to a distributed manager. 2. Capabilities for initiating, suspending, resuming and terminating management scripts. 3. Capabilities to transfer arguments for management scripts. 4. Capabilities to monitor and control running management scripts. 5. Capabilities to transfer the results produced by running management scripts. This memo does not address any additional topics like the generation of notifications or how to address remote agents from a Script MIB implementation.
3.1. Terms
This section defines the terms used throughout this memo. o A `distributed manager' is a processing entity which is capable of performing network management functions. For the scope of this memo, a distributed manager is assumed to implement the Script MIB. o A `higher-level manager', or just `manager', is a processing entity or human who initiates and controls the operations performed by one or more distributed managers. o A `management script' is a set of instructions written in an executable language which implements a management function. o A `management scripting language' is a language used to write management scripts. The term scripting language does not imply that the language must have the characteristics of scripting languages (e.g., string orientation, interpretation, weak typing). The MIB defined in this memo also allows to control management scripts written in arbitrary compiled system programming languages. o A `distributed manager' can be decomposed into an `SNMP entity' which implements the Script MIB defined in this memo and the ` runtime system' that executes scripts. The Script MIB sees the runtime system as the managed resource which is controlled by the MIB. The runtime system can act as an SNMP application, according to the SNMP architecture defined in RFC 2571 [RFC2571]. For example, a runtime system which sends SNMP requests to other SNMP entities will act as a command generator application. The SNMP applications in the runtime system may use the same SNMP engine which also serves the command responder application used to implement the Script MIB, but they are not required to do so. o A `launch button' is the conceptual button used to start the execution of a management script. It assigns control parameters to a management script. In particular, it defines the ownership of the scripts started from a launch button. The ownership can be used by the language runtime system to enforce security profiles on a running management script.
4. Requirements and Design Issues
This section discusses some general requirements that have influenced the design of the Script MIB. o The Script MIB must not make any assumptions about specific languages or runtime systems. o The Script MIB must provide mechanisms that help to avoid new management problems (e.g., script version problems). o The Script MIB must provide SNMP interfaces to all functions required to delegate management scripts. However, other protocols might be used in addition if they provide a significant improvement in terms of convenience for implementation or performance. o The Script MIB must be organized so that access can be controlled effectively by using view-based access control [RFC2575]. The following sections discuss some design issues in more detail.4.1. Script Languages
The Script MIB defined in this memo makes no assumption about the script language. This MIB can therefore be used in combination with different languages (such as Tcl or Java) and/or different versions of the same language. No assumptions are made about the format in which management scripts are transferred. The Script MIB provides access to information about the language versions supported by a Script MIB implementation so that a manager can learn about the capabilities provided by an implementation. Languages and language versions are identified as follows: 1. The language is identified by an object identifier. Object identifier for well-known languages will be registered by the Internet Assigned Numbers Authority (IANA). Enterprise specific languages can also be registered in the enterprise specific OID subtree. 2. A particular version of a language is identified by a language version number. The combination of a language object identifier and a language version is in most cases sufficient to decide whether a script can be executed or not.
3. Different implementations of the same language version might have
differences due to ambiguities in the language definition or
additional language features provided by an implementor. An
additional object identifier value is provided which identifies
the organization which provides the implementation of a language.
This might be used by scripts that require a particular
implementation of a language.
4. Finally, there might be different versions of a language
implementation. A version number for the language implementation
is provided so that the manager can also distinguish between
different implementations from the same organization of a
particular language version.
The version numbers can either be used by a manager to select the
language version required to execute a particular script or to select
a script that fits the language versions supported by a particular
Script MIB implementation.
An additional table lists language extensions that provide features
not provided by the core language. Language extensions are usually
required to turn a general purpose language into a management
language. In many cases, language extensions will come in the form
of libraries that provide capabilities like sending SNMP requests to
remote SNMP agents or accessing the local MIB instrumentation. Every
extension is associated with a language and carries its own version
numbers.
4.2. Script Transfer
There are two different ways to transfer management scripts to a
distributed manager. The first approach requires that the manager
pushes the script to the distributed manager. This is therefore
called the `push model'. The second approach is the `pull model'
where the manager tells the distributed manager the location of the
script and the distributed manager retrieves the script itself.
The MIB defined in this memo supports both models. The `push model'
is realized by a table which allows a manager to write scripts by
sending a sequence of SNMP set requests. The script can be split
into several fragments in order to deal with SNMP message size
limitations.
The `pull model' is realized by the use of Uniform Resource Locators
(URLs) [RFC2396] that point to the script source. The manager writes
the URL which points to the script source to the distributed manager
by sending an SNMP set request. The distributed manager is then responsible for retrieving the document using the protocol specified in the URL. This allows the use of protocols like FTP [RFC959] or HTTP [RFC2616] to transfer large management scripts efficiently. The Script MIB also allows management scripts that are hard-wired into the Script MIB implementation. Built-in scripts can either be implemented in a language runtime system, or they can be built natively into the Script MIB implementation. The implementation of the `push model' or the `pull model' is not required. Scripts can be stored in non-volatile storage. This allows a distributed manager to restart scripts if it is restarted (off-line restart). A manager is not required to push scripts back into the distributed manager after a restart if the script is backed up in non-volatile storage. Every script is identified by an administratively assigned name. This name may be used to derive the name which is used to access the script in non-volatile storage. This mapping is implementation specific. However, the mapping must ensure that the Script MIB implementation can handle scripts with the same administrative name owned by different managers. One way to achieve this is to use the script owner in addition to the script name in order to derive the internal name used to refer to a particular script in non-volatile storage.4.3. Script Execution
The Script MIB permits execution of several instances of the same or different management scripts. Script arguments are passed as OCTET STRING values. Scripts return a single result value which is also an OCTET STRING value. The semantic interpretation of result values is left to the invoking manager or other management scripts. A script invoker must understand the format and semantics of both the arguments and the results of the scripts that it invokes. Scripts can also export complex results through a MIB interface. This allows a management application to access and use script results in the same manner as it processes any other MIB data. However, the Script MIB does not provide any special support for the implementation of MIBs through scripts. Runtime errors terminate active scripts. An exit code and a human readable error message is left in the MIB. A notification containing the exit code, the error message and a timestamp is generated when a script terminates with an error exit code.
Script arguments and results do not have any size limitations other than the limits imposed by the SMI and the SNMP protocol. However, implementations of this MIB might have further restrictions. A script designer might therefore choose to return the results via other mechanisms if the script results can be very large. One possibility is to return a URL as a script result which points to the file containing the script output. Executing scripts have a status object attached which allows script execution to be suspended, resumed, or aborted. The precise semantics of the suspend and resume operations are language and runtime system dependent. Some runtime systems may choose to not implement the suspend/resume operations. A history of finished scripts is kept in the MIB. A script invoker can collect results at a later point in time (offline operation). Control objects can be used to control how entries in the history are aged out if the table fills up.5. Structure of the MIB
This section presents the structure of the MIB. The objects are arranged into the following groups: o language group (smLangTable, smExtsnTable) o script group (smScriptTable) o script code group (smCodeTable) o script launch group (smLaunchTable) o running script group (smRunTable)5.1. Language Group
The smLanguageGroup is used to provide information about the languages and the language extensions supported by a Script MIB implementation. This group includes two tables. The smLangTable lists all languages supported by a Script MIB implementation and the smExtsnTable lists the extensions that are available for a given language.
5.2. Script Group
The smScriptGroup consists of a single table, called the smScriptTable. The smScriptTable lists all scripts known to a Script MIB implementation. The smScriptTable contains objects that allow the following operations: o download scripts from a URL (pull model) o read scripts from local non-volatile storage o store scripts in local non-volatile storage o delete scripts from local non-volatile storage o list permanent scripts (that can not be changed or removed) o read and modify the script status (enabled, disabled, editing) A status object called smScriptOperStatus allows a manager to obtain the current status of a script. It is also used to provide an error indication if an attempt to invoke one of the operations listed above fails. The status change of a script can be requested by modifying the associated smScriptAdminStatus object. The source of a script is defined by the smScriptSource object. This object may contain a URL pointing to a remote location which provides access to the management script. The script source is read from the smCodeTable (described below) or from non-volatile storage if the smScriptSource object contains an empty URL. The smScriptStorageType object is used to distinguish between scripts read from non-volatile storage and scripts read from the smCodeTable. Scripts are automatically loaded once the smScriptAdminStatus object is set to `enabled'. Loading a script includes retrieving the script (probably from a remote location), compiling the script for languages that require a compilation step, and making the code available to the runtime system. The smScriptOperStatus object is used to indicate the status of the loading process. This object will start in the state `retrieving', switch to the state `compiling' and finally reach the state `enabled'. Errors during the retrieval or compilation phase will result in an error state such as `compilationFailed'.
5.3. Code Group
The smCodeGroup consists of a single table, called the smCodeTable, which provides the ability to transfer and modify scripts via SNMP set requests. In particular, the smCodeTable allows the following operations: o download scripts via SNMP (push model) o modify scripts via SNMP (editing) The smCodeTable lists the code of a script. A script can be fragmented over multiple rows of the smCodeTable in order to handle SNMP message size limitations. Modifications of the smCodeTable are only possible if the associated smScriptOperStatus object has the value `editing'. The Script MIB implementation reloads the modified script code once the smScriptOperStatus changes to `enabled' again. The implementation of the smCodeGroup is optional.5.4. Launch Group
The smLaunchGroup contains a single table, the smLaunchTable. An entry in the smLaunchTable represents a launch button which can be used to start a script. The smLaunchTable allows the following operations: o associate a script with an owner used during script execution o provide arguments and parameters for script invocation o invoke scripts with a single set operation The smLaunchTable describes scripts and their parameters that are ready to be launched. An entry in the smLaunchTable attaches an argument to a script and control values which, for example, define the maximum number of times that a script invoked from a particular row in the smLaunchTable may be running concurrently. An entry in the smLaunchTable also defines the owner which will be used to associate permissions with the script execution.5.5. Run Group
The smRunGroup contains a single table, called the smRunTable, which lists all scripts that are currently running or have terminated recently. The smRunTable contains objects that allow the following operations:
o retrieve status information from running scripts o control running scripts (suspend, resume, abort) o retrieve results from recently terminated scripts o control the remaining maximum lifetime of a running script o control how long script results are accessible Every row in the smRunTable contains the argument passed during script invocation, the result produced by the script and the script exit code. The smRunTable also provides information about the current run state as well as start and end time-stamps. There are three writable objects in the smRunTable. The smRunLifeTime object defines the maximum time a running script may run before it is terminated by the Script MIB implementation. The smRunExpireTime object defines the time that a completed script can stay in the smRunTable before it is aged out. The smRunControl object allows running scripts to be suspended, resumed, or aborted.
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