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RFC 4133


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Entity MIB (Version 3)

Part 1 of 3, p. 1 to 14
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Obsoleted by:    6933
Obsoletes:    2737


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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.



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