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RFC 4133

Entity MIB (Version 3)

Pages: 62
Obsoletes:  2737
Obsoleted by:  6933
Part 1 of 3 – Pages 1 to 14
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Network Working Group                                         A. Bierman
Request for Comments: 4133                                 K. McCloghrie
Obsoletes: 2737                                      Cisco Systems, Inc.
Category: Standards Track                                    August 2005


                         Entity MIB (Version 3)

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 (2005).

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 managed objects used for managing multiple logical and physical entities managed by a single SNMP agent. This document specifies version 3 of the Entity MIB, which obsoletes version 2 (RFC 2737).
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Table of Contents

1. The SNMP Management Framework ...................................3 2. Overview ........................................................3 2.1. Terms ......................................................4 2.2. Relationship to Community Strings ..........................5 2.3. Relationship to SNMP Contexts ..............................5 2.4. Relationship to Proxy Mechanisms ...........................6 2.5. Relationship to a Chassis MIB ..............................6 2.6. Relationship to the Interfaces MIB .........................6 2.7. Relationship to the Other MIBs .............................7 2.8. Relationship to Naming Scopes ..............................7 2.9. Multiple Instances of the Entity MIB .......................7 2.10. Re-Configuration of Entities ..............................8 2.11. Textual Convention Change .................................8 2.12. MIB Structure .............................................8 2.12.1. entityPhysical Group ..............................9 2.12.2. entityLogical Group ..............................11 2.12.3. entityMapping Group ..............................11 2.12.4. entityGeneral Group ..............................12 2.12.5. entityNotifications Group ........................12 2.13. Multiple Agents ..........................................12 2.14. Changes Since RFC 2037 ...................................12 2.14.1. Textual Conventions ..............................12 2.14.2. New entPhysicalTable Objects .....................13 2.14.3. New entLogicalTable Objects ......................13 2.14.4. Bug Fixes ........................................13 2.15. Changes Since RFC 2737 ...................................13 2.15.1. Textual Conventions ..............................13 2.15.2. New Objects ......................................14 2.15.3. Bug Fixes ........................................14 3. Definitions ....................................................14 4. Usage Examples .................................................44 4.1. Router/Bridge .............................................44 4.2. Repeaters .................................................50 5. Security Considerations ........................................57 6. IANA Considerations ............................................58 7. Acknowledgements ...............................................59 8. References .....................................................59 8.1. Normative References ......................................59 8.2. Informative References ....................................59
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1. The SNMP Management Framework

For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer to section 7 of RFC 3410 [RFC3410]. Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. MIB objects are generally accessed through the Simple Network Management Protocol (SNMP). Objects in the MIB are defined using the mechanisms defined in the Structure of Management Information (SMI). This memo specifies a MIB module that is compliant to the SMIv2, which is described in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580 [RFC2580].

2. Overview

There is a need for a standardized way of representing a single agent, which supports multiple instances of one MIB. This is presently true for at least 3 standard MIBs, and is likely to become true for more and more MIBs as time passes. For example: - multiple instances of a bridge supported within a single device that has a single agent; - multiple repeaters supported by a single agent; - multiple OSPF backbone areas, each operating as part of its own Autonomous System, and each identified by the same area-id (e.g., 0.0.0.0), supported inside a single router with one agent. The single agent present in each of these cases implies a relationship binds these entities. Effectively, there is some "overall" physical entity which houses the sum of the things managed by that one agent, i.e., there are multiple "logical" entities within a single physical entity. Sometimes, the overall physical entity contains multiple (smaller) physical entities, and each logical entity is associated with a particular physical entity. Sometimes, the overall physical entity is a "compound" of multiple physical entities (e.g., a stack of stackable hubs). What is needed is a way to determine exactly which logical entities are managed by the agent (with some version of SNMP) in order to communicate with the agent about a particular logical entity. When different logical entities are associated with different physical entities within the overall physical entity, it is also useful to be able to use this information to distinguish between logical entities.
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   In these situations, there is no need for varbinds for multiple
   logical entities to be referenced in the same SNMP message (although
   that might be useful in the future).  Rather, it is sufficient, and
   in some situations preferable, to have the context/community in the
   message identify the logical entity to which the varbinds apply.

   Version 2 of this MIB addresses new requirements, which have emerged
   since the publication of the first Entity MIB (RFC 2037 [RFC2037]).
   There is a need for a standardized way of providing non-volatile,
   administratively-assigned identifiers for physical components
   represented with the Entity MIB.  There is also a need to align the
   Entity MIB with the SNMPv3 administrative framework (STD 62, RFC 3411
   [RFC3411]).  Implementation experience has shown that additional
   physical component attributes are also desirable.

   Version 3 of this MIB addresses new requirements, which have emerged
   since the publication of the second Entity MIB (RFC 2737 [RFC2737]).
   There is a need to identify physical entities that are central
   processing units (CPUs) and a need to provide a textual convention
   that identifies an entPhysicalIndex value or zero, where the value
   zero has application-specific semantics.  Two new objects have been
   added to the entPhysicalTable to identify the manufacturing date and
   provide additional URIs for a particular physical entity.

2.1. Terms

Some new terms are used throughout this document: - Naming Scope A "naming scope" represents the set of information that may be potentially accessed through a single SNMP operation. All instances within the naming scope share the same unique identifier space. For SNMPv1, a naming scope is identified by the value of the associated 'entLogicalCommunity' instance. For SNMPv3, the term 'context' is used instead of 'naming scope'. The complete definition of an SNMP context can be found in section 3.3.1 of RFC 3411 [RFC3411]. - Multi-Scoped Object A MIB object, for which identical instance values identify different managed information in different naming scopes, is called a "multi-scoped" MIB object. - Single-Scoped Object A MIB object, for which identical instance values identify the same managed information in different naming scopes, is called a "single-scoped" MIB object.
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   - Logical Entity
     A managed system contains one or more logical entities, each
     represented by at most one instantiation of each of a particular
     set of MIB objects.  A set of management functions is associated
     with each logical entity.  Examples of logical entities include
     routers, bridges, print-servers, etc.

   - Physical Entity
     A "physical entity" or "physical component" represents an
     identifiable physical resource within a managed system.  Zero or
     more logical entities may utilize a physical resource at any given
     time.  Determining which physical components are represented by an
     agent in the EntPhysicalTable is an implementation-specific matter.
     Typically, physical resources (e.g., communications ports,
     backplanes, sensors, daughter-cards, power supplies, the overall
     chassis), which can be managed via functions associated with one or
     more logical entities, are included in the MIB.

   - Containment Tree
     Each physical component may be modeled as 'contained' within
     another physical component.  A "containment-tree" is the conceptual
     sequence of entPhysicalIndex values that uniquely specifies the
     exact physical location of a physical component within the managed
     system.  It is generated by 'following and recording' each
     'entPhysicalContainedIn' instance 'up the tree towards the root',
     until a value of zero indicating no further containment is found.

2.2. Relationship to Community Strings

For community-based SNMP, differentiating logical entities is one (but not the only) purpose of the community string (RFC 1157 [RFC1157]). This is accommodated by representing each community string as a logical entity. Note that different logical entities may share the same naming scope and, therefore, the same values of entLogicalCommunity. This is possible, providing they have no need for the same instance of a MIB object to represent different managed information.

2.3. Relationship to SNMP Contexts

Version 2 of the Entity MIB contains support for associating SNMPv3 contexts with logical entities. Two new MIB objects, defining an SnmpEngineID and ContextName pair, are used together to identify an SNMP context associated with a logical entity. This context can be used (in conjunction with the entLogicalTAddress and entLogicalTDomain MIB objects) to send SNMPv3 messages on behalf of a particular logical entity.
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2.4. Relationship to Proxy Mechanisms

The Entity MIB is designed to allow functional component discovery. The administrative relationships between different logical entities are not visible in any Entity MIB tables. A Network Management System (NMS) cannot determine whether MIB instances in different naming scopes are realized locally or remotely (e.g., via some proxy mechanism) by examining any particular Entity MIB objects. The management of administrative framework functions is not an explicit goal of the Entity MIB WG at this time. This new area of functionality may be revisited after some operational experience with the Entity MIB is gained. Note that for community-based versions of SNMP, a network administrator will likely be able to associate community strings with naming scopes that have proprietary mechanisms, as a matter of configuration. There are no mechanisms for managing naming scopes defined in this MIB.

2.5. Relationship to a Chassis MIB

Some readers may recall that a previous IETF working group attempted to define a Chassis MIB. No consensus was reached by that working group, possibly because its scope was too broad. As such, it is not the purpose of this MIB to be a "Chassis MIB replacement", nor is it within the scope of this MIB to contain all the information which might be necessary to manage a "chassis". On the other hand, the entities represented by an implementation of this MIB might well be contained in a chassis.

2.6. Relationship to the Interfaces MIB

The Entity MIB contains a mapping table identifying physical components that have 'external values' (e.g., ifIndex) associated with them within a given naming scope. This table can be used to identify the physical location of each interface in the ifTable (RFC 2863 [RFC2863]). Because ifIndex values in different contexts are not related to one another, the interface to physical component associations are relative to the same logical entity within the agent. The Entity MIB also contains 'entPhysicalName' and 'entPhysicalAlias' objects, which approximate the semantics of the 'ifName' and 'ifAlias' objects (respectively) from the Interfaces MIB [RFC2863], for all types of physical components.
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2.7. Relationship to the Other MIBs

The Entity MIB contains a mapping table identifying physical components that have identifiers from other standard MIBs associated with them. For example, this table can be used along with the physical mapping table to identify the physical location of each repeater port in the rptrPortTable, or each interface in the ifTable.

2.8. Relationship to Naming Scopes

There is some question as to which MIB objects may be returned within a given naming scope. MIB objects which are not multi-scoped within a managed system are likely to ignore context information in implementation. In such a case, it is likely such objects will be returned in all naming scopes (e.g., not just the 'default' naming scope or the SNMPv3 default context). For example, a community string used to access the management information for logical device 'bridge2' may allow access to all the non-bridge related objects in the 'default' naming scope, as well as a second instance of the Bridge MIB (RFC 1493 [RFC1493]). The isolation of single-scoped MIB objects by the agent is an implementation-specific matter. An agent may wish to limit the objects returned in a particular naming scope to only the multi- scoped objects in that naming scope (e.g., system group and the Bridge MIB). In this case, all single-scoped management information would belong to a common naming scope (e.g., 'default'), which itself may contain some multi-scoped objects (e.g., system group).

2.9. Multiple Instances of the Entity MIB

It is possible that more than one agent may exist in a managed system. In such cases, multiple instances of the Entity MIB (representing the same managed objects) may be available to an NMS. In order to reduce complexity for agent implementation, multiple instances of the Entity MIB are not required to be equivalent or even consistent. An NMS may be able to 'align' instances returned by different agents by examining the columns of each table, but vendor- specific identifiers and (especially) index values are likely to be different. Each agent may be managing different subsets of the entire chassis as well. When all of a physically-modular device is represented by a single agent, the entry (for which entPhysicalContainedIn has the value zero) would likely have 'chassis' as the value of its entPhysicalClass. Alternatively, for an agent on a module where the
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   agent represents only the physical entities on that module (not those
   on other modules), the entry (for which entPhysicalContainedIn has
   the value zero) would likely have 'module' as the value of its
   entPhysicalClass.

   An agent implementation of the entLogicalTable is not required to
   contain information about logical entities managed primarily by other
   agents.  That is, the entLogicalTAddress and entLogicalTDomain
   objects in the entLogicalTable are provided to support an historical
   multiplexing mechanism, not to identify other SNMP agents.

   Note that the Entity MIB is a single-scoped MIB, in the event an
   agent represents the MIB in different naming scopes.

2.10. Re-Configuration of Entities

Most of the MIB objects defined in this MIB have, at most, a read- only MAX-ACCESS clause. This is a conscious decision by the working group to limit this MIB's scope. The second version of the Entity MIB allows a network administrator to configure some common attributes of physical components.

2.11. Textual Convention Change

Version 1 of the Entity MIB contains three MIB objects defined with the (now obsolete) DisplayString textual convention. In version 2 of the Entity MIB, the syntax for these objects has been updated to use the (now preferred) SnmpAdminString textual convention. The working group realizes that this change is not strictly supported by SMIv2. In our judgment, the alternative of deprecating the old objects and defining new objects would have a more adverse impact on backward compatibility and interoperability, given the particular semantics of these objects.

2.12. MIB Structure

The Entity MIB contains five groups of MIB objects: - entityPhysical group Describes the physical entities managed by a single agent. - entityLogical group Describes the logical entities managed by a single agent.
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   - entityMapping group
     Describes the associations between the physical entities, logical
     entities, interfaces, and non-interface ports managed by a single
     agent.

   - entityGeneral group
     Describes general system attributes shared by potentially all types
     of entities managed by a single agent.

   - entityNotifications group
     Contains status indication notifications.

2.12.1. entityPhysical Group

This group contains a single table to identify physical system components, called the entPhysicalTable. The entPhysicalTable contains one row per physical entity, and must always contain at least one row for an "overall" physical entity, which should have an entPhysicalClass value of 'stack(11)', 'chassis(3)' or 'module(9)'. Each row is indexed by an arbitrary, small integer, and contains a description and type of the physical entity. It also optionally contains the index number of another entPhysicalEntry, indicating a containment relationship between the two. Version 2 of the Entity MIB provides additional MIB objects for each physical entity. Some common read-only attributes have been added, as well as three writable string objects. - entPhysicalAlias This string can be used by an NMS as a non-volatile identifier for the physical component. Maintaining a non-volatile string for every physical component represented in the entPhysicalTable can be costly and unnecessary. An agent may algorithmically generate 'entPhysicalAlias' strings for particular entries (e.g., based on the entPhysicalClass value). - entPhysicalAssetID This string is provided to store a user-specific asset identifier for removable physical components. In order to reduce the non- volatile storage needed by a particular agent, a network administrator should only assign asset identifiers to physical entities that are field-replaceable (i.e., not permanently contained within another physical entity).
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   - entPhysicalSerialNum
     This string is provided to store a vendor-specific serial number
     string for physical components.  This writable object is used when
     an agent cannot identify the serial numbers of all installed
     physical entities, and a network administrator wishes to configure
     the non-volatile serial number strings manually (via an NMS
     application).

   Version 3 of the Entity MIB provides two additional MIB objects for
   each physical entity:

   - entPhysicalMfgDate
     This object contains the date of manufacturing of the managed
     entity.  If the manufacturing date is unknown or not supported the
     object is not instantiated.  The special value '0000000000000000'H
     may also be returned in this case.

   - entPhysicalUris
     This object provides additional identification information about
     the physical entity.

     This object contains one or more Uniform Resource Identifiers
     (URIs) and, therefore, the syntax of this object must conform to
     RFC 3986 [RFC3986] section 2.  Uniform Resource Names (URNs), RFC
     3406 [RFC3406], are resource identifiers with the specific
     requirements for enabling location independent identification of a
     resource, as well as longevity of reference.  URNs are part of the
     larger URI family with the specific goal of providing persistent
     naming of resources.  URI schemes and URN name spaces are
     registered by IANA (see http://www.iana.org/assignments/uri-schemes
     and http://www.iana.org/assignments/urn-namespaces).

     For example, the entPhysicalUris object may be used to encode a URI
     containing a Common Language Equipment Identifier (CLEI) URN for
     the managed physical entity.  The URN name space for CLEIs is
     defined in [RFC4152], and the CLEI format is defined in
     [T1.213][T1.213a].  For example, an entPhysicalUris instance may
     have the value of

        URN:CLEI:D4CE18B7AA

     [RFC3986] and [RFC4152] identify this as a URI in the CLEI URN name
     space.  The specific CLEI code, D4CE18B7AA, is based on the example
     provided in [T1.213a].

     Multiple URIs may be present and are separated by white space
     characters.  Leading and trailing white space characters are
     ignored.
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     If no additional identification information is known about the
     physical entity or supported, the object is not instantiated.

2.12.2. entityLogical Group

This group contains a single table to identify logical entities, called the entLogicalTable. The entLogicalTable contains one row per logical entity. Each row is indexed by an arbitrary, small integer and contains a name, description, and type of the logical entity. It also contains information to allow access to the MIB information for the logical entity. This includes SNMP versions that use a community name (with some form of implied context representation) and SNMP versions that use the SNMP ARCH [RFC3411] method of context identification. If an agent represents multiple logical entities with this MIB, then this group must be implemented for all logical entities known to the agent. If an agent represents a single logical entity, or multiple logical entities within a single naming scope, then implementation of this group may be omitted by the agent.

2.12.3. entityMapping Group

This group contains three tables to identify associations between different system components. - entLPMappingTable This table contains mappings between entLogicalIndex values (logical entities) and entPhysicalIndex values (the physical components supporting that entity). A logical entity can map to more than one physical component, and more than one logical entity can map to (share) the same physical component. If an agent represents a single logical entity, or multiple logical entities within a single naming scope, then implementation of this table may be omitted by the agent. - entAliasMappingTable This table contains mappings between entLogicalIndex, entPhysicalIndex pairs, and 'alias' object identifier values. This allows resources managed with other MIBs (e.g., repeater ports, bridge ports, physical and logical interfaces) to be identified in the physical entity hierarchy. Note that each alias identifier is only relevant in a particular naming scope. If an agent represents
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     a single logical entity, or multiple logical entities within a
     single naming scope, then implementation of this table may be
     omitted by the agent.

   - entPhysicalContainsTable
     This table contains simple mappings between
     'entPhysicalContainedIn' values for each container/'containee'
     relationship in the managed system.  The indexing of this table
     allows an NMS to quickly discover the 'entPhysicalIndex' values for
     all children of a given physical entity.

2.12.4. entityGeneral Group

This group contains general information relating to the other object groups. At this time, the entGeneral group contains a single scalar object (entLastChangeTime), which represents the value of sysUptime when any part of the Entity MIB configuration last changed.

2.12.5. entityNotifications Group

This group contains notification definitions relating to the overall status of the Entity MIB instantiation.

2.13. Multiple Agents

Even though a primary motivation for this MIB is to represent the multiple logical entities supported by a single agent, another motivation is to represent multiple logical entities supported by multiple agents (in the same "overall" physical entity). Indeed, it is implicit in the SNMP architecture that the number of agents is transparent to a network management station. However, there is no agreement at this time as to the degree of cooperation that should be expected for agent implementations. Therefore, multiple agents within the same managed system are free to implement the Entity MIB independently. (For more information, refer to Section 2.9, "Multiple Instances of the Entity MIB".)

2.14. Changes Since RFC 2037

2.14.1. Textual Conventions

The PhysicalClass TC text has been clarified, and a new enumeration to support 'stackable' components has been added. The SnmpEngineIdOrNone TC has been added to support SNMPv3.
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2.14.2. New entPhysicalTable Objects

The entPhysicalHardwareRev, entPhysicalFirmwareRev, and entPhysicalSoftwareRev objects have been added for revision identification. The entPhysicalSerialNum, entPhysicalMfgName, entPhysicalModelName, and entPhysicalIsFru objects have been added for better vendor identification for physical components. In the event the agent cannot identify this information, the entPhysicalSerialNum object can be set by a management station. The entPhysicalAlias and entPhysicalAssetID objects have been added for better user component identification. These objects are intended to be set by a management station and preserved by the agent across restarts.

2.14.3. New entLogicalTable Objects

The entLogicalContextEngineID and entLogicalContextName objects have been added to provide an SNMP context for SNMPv3 access on behalf of a logical entity.

2.14.4. Bug Fixes

A bug was fixed in the entLogicalCommunity object. The subrange was incorrect (1..255) and is now (0..255). The description clause has also been clarified. This object is now deprecated. The entLastChangeTime object description has been changed to generalize the events that cause an update to the last change timestamp. The syntax was changed from DisplayString to SnmpAdminString for the entPhysicalDescr, entPhysicalName, and entLogicalDescr objects.

2.15. Changes Since RFC 2737

2.15.1. Textual Conventions

The PhysicalIndexOrZero TC has been added to allow objects to reference an entPhysicalIndex value or zero. The PhysicalClass TC has been extended to support a new enumeration for central processing units.
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2.15.2. New Objects

The entPhysicalMfgDate object has been added to the entPhysicalTable to provide the date of manufacturing of the managed entity. The entPhysicalUris object has been added to the entPhysicalTable to provide additional identification information about the physical entity, such as a Common Language Equipment Identifier (CLEI) URN.

2.15.3. Bug Fixes

The syntax was changed from INTEGER to Integer32 for the entPhysicalParentRelPos, entLogicalIndex, and entAliasLogicalIndexOrZero objects, and from INTEGER to PhysicalIndexOrZero for the entPhysicalContainedIn object.


(page 14 continued on part 2)

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