Network Working Group K. McCloghrie Request for Comments: 2037 A. Bierman Category: Standards Track Cisco Systems October 1996 Entity MIB using SMIv2 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. Table of Contents 1. Introduction .............................................. 2 2. The SNMP Network Management Framework ..................... 2 2.1 Object Definitions ....................................... 2 3. Overview .................................................. 3 3.1 Terms .................................................... 4 3.2 Relationship to Community Strings ........................ 5 3.3 Relationship to Proxy Mechanisms ......................... 5 3.4 Relationship to a Chassis MIB ............................ 5 3.5 Relationship to the Interfaces MIB ....................... 6 3.6 Relationship to the Other MIBs ........................... 6 3.7 Relationship to Naming Scopes ............................ 6 3.8 Multiple Instances of the Entity MIB ..................... 7 3.9 Re-Configuration of Entities ............................. 7 3.10 MIB Structure ........................................... 7 3.10.1 entityPhysical Group .................................. 8 3.10.2 entityLogical Group ................................... 8 3.10.3 entityMapping Group ................................... 8 3.10.4 entityGeneral Group ................................... 9 3.10.5 entityNotifications Group ............................. 9 3.11 Multiple Agents ......................................... 9 4. Definitions ............................................... 10 5. Usage Examples ............................................ 26 5.1 Router/Bridge ............................................ 26 5.2 Repeaters ................................................ 30 6. Acknowledgements .......................................... 33 7. References ................................................ 34 8. Security Considerations ................................... 35 9. Authors' Addresses ........................................ 35 McCloghrie & Bierman Standards Track [Page 1] RFC 2037 Entity MIB using SMIv2 October 1996 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 managing multiple logical and physical entities managed by a single SNMP agent. 2. The SNMP Network Management Framework The SNMP Network Management Framework presently consists of three major components. They are: o the SMI, described in RFC 1902 [1], - the mechanisms used for describing and naming objects for the purpose of management. o the MIB-II, STD 17, RFC 1213 [2], - the core set of managed objects for the Internet suite of protocols. o the protocol, RFC 1157 [6] and/or RFC 1905 [4], - the protocol for accessing managed information. Textual conventions are defined in RFC 1903 [3], and conformance statements are defined in RFC 1904 [5]. The Framework permits new objects to be defined for the purpose of experimentation and evaluation. This memo specifies a MIB module that is compliant to the SNMPv2 SMI. A semantically identical MIB conforming to the SNMPv1 SMI can be produced through the appropriate translation. 2.1. Object Definitions Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the subset of Abstract Syntax Notation One (ASN.1) defined in the SMI. In particular, each object type is named by an OBJECT IDENTIFIER, an administratively assigned name. The object type together with an object instance serves to uniquely identify a specific instantiation of the object. For human convenience, we often use a textual string, termed the descriptor, to refer to the object type. McCloghrie & Bierman Standards Track [Page 2] RFC 2037 Entity MIB using SMIv2 October 1996 3. 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 having a single agent; - multiple repeaters supported by a single agent; - multiple OSPF backbone areas, each one 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 fact that it is a single agent in each of these cases implies there is some relationship which binds all of these entities together. 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 what logical entities are managed by the agent (either by SNMPv1 or SNMPv2), and thereby to be able 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. 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. McCloghrie & Bierman Standards Track [Page 3] RFC 2037 Entity MIB using SMIv2 October 1996 3.1. 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. - 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. - 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. It is an implementation-specific manner as to which physical components are represented by an agent in the EntPhysicalTable. 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 optionally be modeled as 'contained' within another physical component. A "containment-tree" is the conceptual sequence of entPhysicalIndex values which 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. McCloghrie & Bierman Standards Track [Page 4] RFC 2037 Entity MIB using SMIv2 October 1996 Note that chassis slots, which are capable of accepting one or more module types from one or more vendors, are modeled as containers in this MIB. The value of entPhysicalContainedIn for a particular 'module' entity (entPhysicalClass value of 'module(9)') must be equal to an entPhysicalIndex that represents the parent 'container' entity (associated entPhysicalClass value of ('container(5)'). An agent must represent both empty and full containers in the entPhysicalTable. 3.2. Relationship to Community Strings For community-based SNMP, distinguishing between different logical entities is one (but not the only) purpose of the community string [6]. 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. 3.3. 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. An 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 a network administrator will likely be able to associate community strings with naming scopes with proprietary mechanisms, as a matter of configuration. There are no mechanisms for managing naming scopes defined in this MIB. 3.4. 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 McCloghrie & Bierman Standards Track [Page 5] RFC 2037 Entity MIB using SMIv2 October 1996 entities represented by an implementation of this MIB might well be contained in a chassis. 3.5. 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 [7]. Since 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 an 'entPhysicalName' object, which approximates the semantics of the ifName object from the Interfaces MIB [7] for all types of physical components. 3.6. 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. 3.7. 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 'main' naming scope). 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 'main' naming scope, as well as a second instance of the Bridge MIB. It is an implementation-specific matter as to the isolation of single-scoped MIB objects by the agent. An agent may wish to limit the objects returned in a particular naming scope to just 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. 'main'), which itself may contain some multi-scoped objects (e.g. system group). McCloghrie & Bierman Standards Track [Page 6] RFC 2037 Entity MIB using SMIv2 October 1996 3.8. Multiple Instances of the Entity MIB It is possible that more than one agent exists in a managed system, and 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 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. 3.9. Re-Configuration of Entities All the MIB objects defined in this MIB have at most a read-only MAX-ACCESS clause, i.e., none