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An Architecture for Describing SNMP Management Frameworks 1 August 1997 D. Harrington Cabletron Systems, Inc. dbh@cabletron.com B. Wijnen IBM T.J. Watson Research wijnen@vnet.ibm.com <draft-ietf-snmpv3-next-gen-arch-04.txt> Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Abstract This document describes an architecture for describing SNMP Management Frameworks. The architecture is designed to be modular to allow the evolution of the SNMP protocol standards over time. The major portions of the architecture are an SNMP engine containing a Message Processing Subsystem, a Security Subsystem and an Access Control Subsystem, and possibly multiple SNMP applications which provide specific functional processing of network management data. Harrington/Wijnen Expires February 1998 [Page 1] Draft An Architecture for SNMP Management Frameworks August 1997 0. Issues 0.1. Resolved Issues . contextEngineID in reportPDU = snmpEngineID of report generator . returnResponsePDU - are all parameters needed? overrides allowed? all parameters kept for future flexibility overrides not supported by SNMPv3 . use of IN/OUT indicators in primitives accepted . NT/Unix-like access control - can be defined as future model . user-friendly names? yes, but with limits . SnmpAdminString as index? yes, but restrict sizes . need both MMS and maxSizeResponseScopedPDU? yes. . synchronous vs. asynchronous primitives? synchronous preferred . should we change MIB naming? no, it is acceptable . is it ok that USM is bound to SNMPv3? while undesirable, it is acceptable. A cleaner model may be defined in the future. . should securityModel "any" be supported? for ACM use, not SNMPv3 . what defines SNMPv3? a document will be published after Munich . Is an application-level handle needed for request/response matching? yes. create sendPduhandle . Is wildcard contextEngineID/pduType registration needed? No. This is an internal interface, and wildcarding can be supported by an implementation, but is not required in the standard. . Should indices be integers or SnmpAdminStrings? SnmpAdminStrings is the consensus. . Should protocols be identified as OIDs or Integers? OIDs . terminology: securityLevel rather than LoS msgXXXX to identify message fields in SNMPv3 . OID or Integer for auth/priv protocol identifiers Consensus: use OID . Is Glossary needed to describe primitive parameters, or is the expanded template adequate for this purpose? Consensus: Terms are basically all defined in section 3. . state_reference releases Consensus: documents checked; we think it is OK now . new SnmpEngineID format rules to be discussed yet. Consensus: Limit size to be 1..32 . needs changes to meet STDGUIDE guidelines We think we're meeting them now . we punted snmpEngineMaxMessageSize at 2nd interim because that info travels in each SNMPv3 message. However, we may want to re-introduce it so that SNMPv1/v2c managers can learn the value!! Consensus: Nobody picked up on this, so it seems not needed. . Do we need a mechanism to discover securityModels supported Can be decided after Munich . add a "Decision History" section (as an appendix?) Can be decided after Munich Harrington/Wijnen Expires February 1998 [Page 2] Draft An Architecture for SNMP Management Frameworks August 1997 0.1.1. Issues discussed at second Interim Meeting: . A "readable" introduction supplement may be done after Munich. . Applications are responsible for retries, but implementations may differ. . TCs should not be defined just to describe primitive parameters. If they cannot be described adequately in text, they can be defined in a Glossary. Avoid describing implementation details. . Is SnmpAdminString appropriate for all strings, such as securityIdentifier and context and group? These had different sizes and semantics. size and semantics may be defined in syntax and description of OBJECT . AdminString has size (0..255); revisit for utf8 discussions . securityModel #s - 00 for IETF standards; from v2* documents . protocol IDs - integer or OID? voted 13-0 for OID. . uniqueness of securityName . mapping between principal and securityName is outside scope of WG. . principals may have more than one securityName in an entity . mappings may exist between many types of MDID and a single securityName . mappings may exist between different (model, Name) and the same securityName by varying the model or the Name. . the securityName and a MDID may be identical. This can be defined by the Security Model. (user,"public") may map to securityName "public" . [securityName, securityModel] yields zero or one MDName, with exceptions for backwards compatibility. The exception is defined by the model, and the problems are the province of the model to resolve. Harrington/Wijnen Expires February 1998 [Page 3] Draft An Architecture for SNMP Management Frameworks August 1997 0.2. Change Log [version 4.14] . formatting . pagination [version 4.13] . new acknowledgements . updated references . updated issues list . ordered security, editors, acknowledgements, references sections . checked line lengths [version 4.12] . cleanup . added expectResponse to processIncomingMsg to address Levi-raised concern . acknowledgements . MIB checked by SMICng . post to snmpv3 mailing list [version 4.11] . Change Primitives between MP and SEC to try and address the issue of architectural binding to message format. . Added securityName and securityLevel to the returnResponsePdu primitive so that architecturally it could be different for a request and a response. . Rename processMsg primitive to processIncomingMsg [version 4.10] . spell check [version 4.9] . editorial changes . fix SnmpEngineID TC . add a note to SnmpAdminString . rename title of section 1.1 . expand description of Dispatcher a bit [version 4.8] . Added parameter pduVersion on primitives: sendPdu processPdu returnResponsePdu processResponsePdu prepareDataElements prepareOutgoingMessage prepareResponseMessage . Added parameter messageProcessingModel on the primitive: processPdu processResponsePdu returnResponsePdu . Removed messageProcessingModel parameter from primitives: registerContextEngineID Harrington/Wijnen Expires February 1998 [Page 4] Draft An Architecture for SNMP Management Frameworks August 1997 unregisterContextEngineID . Renamed SNMP Version Multiplexer to Dispatcher . Renamed Version Multiplexer to Message Multiplexer . Renamed Application Multiplexer to PDU Dispatcher . Rearranged some parameters in various Primitives so the sequence of parameters is now more consistent. [version 4.7] . editorial cleanup . changed asterisk text . modified snmpv3 framework description to eliminate dependencies . reorder 4.2.x to reflect transaction order . changed SnmpEngineID size to 1..32 [version 4.6] . Changes to use synchronous primitives where possible . Changes to describe SNMP Version Multiplexer . Remove (empty) glossary . Redraw documentation figure . Redraw Operational Overview Figure . Remove old section 4 (Architectural Elements of Procedure) These moved to the MP document into the SNMP Version Multiplexer section. . Move Overview of all primitives from Appendix to Section 4. . Simplify Appendix A to just described Model Designer Guidelines and refer back to section 4 for specific primitives . Remove Appendix B (An Evolutionary Architecture - Design Goals) . added design decision regarding security . Included latest Snmp SecurityModel TC (as it was actually posted to the SNMPv3 mailing list). [version 4.5] . start with <draft-ietf-snmpv3-next-gen-arch-03.txt> . change vendor to implementor . change LoS to securityLevel . remove mention of enterprise . change Internet Management Framework to SNMP Management Framework . modify usage of "frameworks" to improve internal consistency. . change Message Processing Abstract Service Interface to Application Multiplexor . change description of SNMP engine . moved "one-to-one association" for entity and engine to discussion of engine. . changed distributing to dispatching . added asterisks to indicate v3* items are also not required. . changed "community access control" to "other access control" . added TC for SnmpMessageProcessingModel . modified Security Considerations . modified acknowledgements [version 4.4] Harrington/Wijnen Expires February 1998 [Page 5] Draft An Architecture for SNMP Management Frameworks August 1997 . Fixed one error in the MIB (found with SMICng) . Reformatted text for SnmpAdminString, no change in text. . Changed text for SnmpEngineID.. this is still under discussion. But this new text seems to be getting close to what we want. . Added an issue w.r.t. snmpEngineMaxMessageSize . adapt Primitive names and parameters to very latest (july 11) names . removed blank lines before the .p page controls. . publish as <draft-ietf-snmpv3-next-gen-arch-03.txt> [version 4.3] . some minor editing adjustments [version 4.2] . modify abstract so there is no requirement for one entity to contain both a command generator and a notification receiver. . modify Introduction list of entities which are meant to be supported . reorganized sections 1 through 4 for more consistency in contents. . described section contents in Introduction:Target Audience . move documentation descriptions to section 2 . rewrite section 4 to be more like a real elements of procedure. . modified SnmpSecurityModel and SnmpEngineID definitions . replaced MIB with Bert's replacement . added Randy's TC for SnmpAdminString . modified the example algorithm text for SnmpEngineID . rewrote security considerations for brevity. . modified "context" description . moved "Threats" to Goals/Requirements . eliminated snmpEngineMaxMessageSize object . posted to snmpv3 (by DBH) [version 4.1] . Adopt "abstract" to new terminology . Addressed all comments I (BW) made to DBH in an earlier email . Changed Introduction section to new terminology . changed wording for "implementation" to indicate it may contain multiple models. . Section 2. Started some wording on Goals and Design decisions . Added the overview picture of a traditional agent and a traditional manager. This is in section 2. . Changed overview figure in section 3. to address the comments by Dave Levi. It now lists the type of applications . At various places ensure that text (easily) fits within 72 columns as required by RFC-editors Guidelines document. . Section 2.3 (new section) has the documents set overview. I verified the claims about standards. Not sure I worded the SNMPv2 std correctly,. We'll hear it if we did it wrong. . Section 2.4 (new section) gives overview of SNMP entities based on modified Dave Levi figure. I (Bert) wonder however if it would not be better to move it to after section 3.1.13 . Section 3. Added more figures... please let us know if you find then useful and/or helpful. We could also move these back to section 2 if such makes more sense. Harrington/Wijnen Expires February 1998 [Page 6] Draft An Architecture for SNMP Management Frameworks August 1997 . Added a picture in section 3.2. It also shows some of access control, so not sure it really fits here, although it does map principal to model dependent security ID to securityName . Replace "<" with "is lower than" in section 3.4.3 which seems better in a text document. . Renamed section 4.1 to "SNMP engine processing" instead of "The Message Processing Subsystem" because the transport mappings, mpc multiplexor and such is done in ARCH document so it is done "in general in the engine" and it passes a specific message to a Message Processing Subsystem. . "bulletized" some stuff in section 4.2 and 4.3. Dave, this is just how I (Bert) like it better. Feel free to undo it if you strongly disagree . Section 4.3 changed "initiate a transaction" to "originate a notification". . Inserted title line for section 4.4 (I think it was missing) I have named it "Information Model" in accordance with the change I made (after Russ's comments) in the document figure to lump SMI, TC and Conformance together. . Inserted a title for section 4.5 named "Operational Model" to get in sync with the the lumping together of ProtoOps and Transport Mappings in document overview . Renumber section 4.4.4 to 4,5,1 and added 4.5.2 to follow the document overview figure. If we really want to follow it, then maybe we should also reorder some of these sections. Like Access Control seems specifically misplaced. So I decided to move it before applications as section 4.3, so the 4.x above should all be read as 4.x+1 . Removed size from SnmpEngineID TC... why did you limit it to (0..2048). Did we not decide to leave it open? . Should we not remove snmpEngineMaxMessageSize from the MIB. That was agreed at 2nd interim. It travels in every message and so seems to be useless. However, I think it could indeed still help SNMPv1 or SNMPv2c managers. . I kept your definitions of registration-points for auth and priv protocols, but my recollection is that they would be completely removed from ARCH and that it would all be done in SEC document. . Modified Security Considerations. Was still talking about LPM. . Appendix. I am still wondering if we need to use capitals for things like "Security Model" "Subsystem" and such. This is only an appendix... but we better be consistent, no? Anyway I changed it so it is consistent (at least I tried). . Appendix, renamed imf to snmpFramework . Appendix, changed state_reference and state_release to stateReference and stateRelease to be consistent with other names for abstract data and primitives. . A.2 changed MessageEngine to SNMP engine . Fixed ASI primitives to be in sync with SEC document. I also thought that our ARCH document-outline wanted to at least have the primitives listed within the main body of the text, no? Harrington/Wijnen Expires February 1998 [Page 7] Draft An Architecture for SNMP Management Frameworks August 1997 . Adapted send_pdu to sendPdu primitive as reconciled by Randy In fact I made sure all primitives are in-line with current agreement on names and parameters. . Rename title of A.2.4 and A.2.5 so it fits on 1 line in contents . I did not look at appendix B. That is your (DBH) specialty is it not ? ;-). . Quick simple spell check done with "spell" on AIX [version 4.0] . move section 7 - Model Requirements to an appendix . move Section 3 - Design Goals to an appendix . modified Section 5 - Naming . remove "possibly multiple" . moved Section 5 to Section 3 . change orangelets to applications . modify description of applications . change scopedPDU-MMS and PDU-MMS to maxSizeResponseScopedPDU . change Scoped-PDU and ScopedPDU to scopedPDU (no dash, lower case S) . change imfxxx to snmpFrameworkxxx . change security-entity to principal . change securityIdentity to securityName . change MIID to securityName . eliminate all reference to groupName or group . LoS ordering noAuthNoPriv < authNoPriv < authPriv . Los TC naming - noAuthNoPriv(1), authNoPriv(2), authPriv(3) . remove TCs not used in MIBs - securityIdentity TC etc . changed Message Processing and Control to Message Processing . changed future tense to present tense . eliminate messageEngine . added/updated primitives . addressed issues raised on the mailing list [version 3.1] . change securityIdentity to MIID . write text to explain the differences between security-identities, model-dependent identifiers, and model-independent identifiers. . write text to explain distinction within the LCD of the security data, the access control data, and the orangelet data. . identify issues . publish as <draft-ietf-snmpv3-next-gen-arch-02.txt> [version 3.0] . add section on threats for message security . add section on threats for access control . change application to orangelet . remove references to F-Ts . change securityIdentity to security-identity . change securityCookie to securityIdentity . the format of securityIdentity is defined by the model . add securityModel to passed parameters as needed . eliminate group from passed parameters . remove unused IMPORTS Harrington/Wijnen Expires February 1998 [Page 8] Draft An Architecture for SNMP Management Frameworks August 1997 . add glossary section with initial set of words to define . differentiate the messageEngine from the contextEngine . eliminate the term SNMPng . rewrote 1.1. A Note on Terminology . eliminated assumptions about SNMP processing always being message related . rewrote 4.x to reflect new thinking . rewrote 5.x to reflect new thinking . rewrote 6.x (the MIB) to reflect new thinking . added MIB objects at this level (previously only TCs) . rewrote 7.x . sent to v3edit list Harrington/Wijnen Expires February 1998 [Page 9] Draft An Architecture for SNMP Management Frameworks August 1997 1. Introduction 1.1. Overview This document assumes an audience with varying levels of technical understanding of SNMP. This document does not provide a general introduction to SNMP. Other documents and books can provide a much better introduction to SNMP. Nor does this document provide a history of SNMP. That also can be found in books and other documents. This document defines a vocabulary for describing SNMP Management Frameworks, and an architecture for describing the major portions of SNMP Management Frameworks. Section 1 describes the purpose, goals, and design decisions of this architecture. Section 2 describes various types of documents which define SNMP Frameworks, and how they fit into this architecture. It also provides a minimal roadmap to the documents which have previously defined SNMP frameworks. Section 3 details the vocabulary of this architecture and its pieces. This section is important for understanding the remaining sections, and for understanding documents which are written to fit within this architecture. Section 4 describes the primitives used for the abstract service interfaces between the various subsystems, models and applications within this architecture. Section 5 defines a collection of managed objects used to instrument SNMP entities within this architecture. Sections 6, 7, 8, and 9 are administrative in nature. Appendix A contains guidelines for designers of Models which are expected to fit within this architecture. 1.2. SNMP Management Systems An SNMP management system contains: - several (potentially many) nodes, each with an SNMP entity containing command responder and notification originator applications, which have access to management instrumentation; - at least one SNMP entity containing command generator and/or notification receiver applications; and, - a management protocol, used to convey management information between the SNMP entities. Harrington/Wijnen Expires February 1998 [Page 10] Draft An Architecture for SNMP Management Frameworks August 1997 SNMP entities executing command generator and notification receiver applications monitor and control managed elements. Managed elements are devices such as hosts, routers, terminal servers, etc., which are monitored and controlled via access to their management information. It is the purpose of this document to define an architecture which can evolve to realize effective network management in a variety of configurations and environments. The architecture has been designed to meet the needs of implementations of: - minimal SNMP entities with command responder and/or notification originator applications (traditionally called SNMP agents), - SNMP entities with proxy forwarder applications (traditionally called SNMP proxy agent), - command line driven SNMP entities with command generator and/or notification receiver applications (traditionally called SNMP command line managers), - SNMP entities with command generator and/or notification receiver, plus command responder and/or notification originator applications (traditionally called SNMP mid-level managers or dual-role entities), - SNMP entities with command generator and/or notification receiver and possibly other types of applications for managing a potentially very large number of managed nodes (traditionally called network management stations). 1.3. Goals of this Architecture This architecture was driven by the following goals: - Use existing materials as much as possible. It is heavily based on previous work, informally known as SNMPv2u and SNMPv2*. - Address the need for secure SET support, which is considered the most important deficiency in SNMPv1 and SNMPv2c. - Make it possible to move portions of the architecture forward in the standards track, even if consensus has not been reached on all pieces. - Define an architecture that allows for longevity of the SNMP Frameworks that have been and will be defined. - Keep SNMP as simple as possible. - Make it relatively inexpensive to deploy a minimal conformant implementation - Make it possible to upgrade portions of SNMP as new approaches become available, without disrupting an entire SNMP framework. - Make it possible to support features required in large networks, but make the expense of supporting a feature directly related to the support of the feature. Harrington/Wijnen Expires February 1998 [Page 11] Draft An Architecture for SNMP Management Frameworks August 1997 1.4. Security Requirements of this Architecture Several of the classical threats to network protocols are applicable to the network management problem and therefore would be applicable to any Security Model used in an SNMP Management Framework. Other threats are not applicable to the network management problem. This section discusses principal threats, secondary threats, and threats which are of lesser importance. The principal threats against which any Security Model used within this architecture SHOULD provide protection are: Modification of Information The modification threat is the danger that some unauthorized SNMP entity may alter in-transit SNMP messages generated on behalf of an authorized principal in such a way as to effect unauthorized management operations, including falsifying the value of an object. Masquerade The masquerade threat is the danger that management operations not authorized for some principal may be attempted by assuming the identity of another principal that has the appropriate authorizations. Message Stream Modification The SNMP protocol is typically based upon a connectionless transport service which may operate over any subnetwork service. The re-ordering, delay or replay of messages can and does occur through the natural operation of many such subnetwork services. The message stream modification threat is the danger that messages may be maliciously re-ordered, delayed or replayed to an extent which is greater than can occur through the natural operation of a subnetwork service, in order to effect unauthorized management operations. Disclosure The disclosure threat is the danger of eavesdropping on the exchanges between SNMP engines. Protecting against this threat may be required as a matter of local policy. There are at least two threats against which a Security Model within this architecture need not protect. Denial of Service A Security Model need not attempt to address the broad range of attacks by which service on behalf of authorized users is denied. Indeed, such denial-of-service attacks are in many cases indistinguishable from the type of network failures with which any viable network management protocol must cope as a matter of course. Traffic Analysis Harrington/Wijnen Expires February 1998 [Page 12] Draft An Architecture for SNMP Management Frameworks August 1997 A Security Model need not attempt to address traffic analysis attacks. Many traffic patterns are predictable - entities may be managed on a regular basis by a relatively small number of management stations - and therefore there is no significant advantage afforded by protecting against traffic analysis. 1.5. Design Decisions Various designs decision were made in support of the goals of the architecture and the security requirements: - Architecture An architecture should be defined which identifies the conceptual boundaries between the documents. Subsystems should be defined which describe the abstract services provided by specific portions of an SNMP framework. Abstract service interfaces, as described by service primitives, define the abstract boundaries between documents, and the abstract services that are provided by the conceptual subsystems of an SNMP framework. - Self-contained Documents Elements of procedure plus the MIB objects which are needed for processing for a specific portion of an SNMP framework should be defined in the same document, and as much as possible, should not be referenced in other documents. This allows pieces to be designed and documented as independent and self-contained parts, which is consistent with the general SNMP MIB module approach. As portions of SNMP change over time, the documents describing other portions of SNMP are not directly impacted. This modularity allows, for example, Security Models, authentication and privacy mechanisms, and message formats to be upgraded and supplemented as the need arises. The self-contained documents can move along the standards track on different time-lines. - The Security Models in the Security Subsystem SHOULD protect against the principal threats: modification of information, masquerade, message stream modification and disclosure. They do not need to protect against denial of service and traffic analysis. - Remote Configuration The Security and Access Control Subsystems add a whole new set of SNMP configuration parameters. The Security Subsystem also requires frequent changes of secrets at the various SNMP entities. To make this deployable in a large operational environment, these SNMP parameters must be able to be remotely configured. - Controlled Complexity It is recognized that simple managed devices want to keep the resources used by SNMP to a minimum. At the same time, there Harrington/Wijnen Expires February 1998 [Page 13] Draft An Architecture for SNMP Management Frameworks August 1997 is a need for more complex configurations which can spend more resources for SNMP and thus provide more functionality. The design tries to keep the competing requirements of these two environments in balance and allows the more complex environments to logically extend the simple environment. Harrington/Wijnen Expires February 1998 [Page 14] Draft An Architecture for SNMP Management Frameworks August 1997 2. Documentation Overview The following figure shows the set of documents that fit within the SNMP Architecture. +-------------------------- Document Set ----------------------------+ | | | +------------+ +-----------------+ +----------------+ | | | Document * | | Applicability * | | Coexistence * | | | | Roadmap | | Statement | | & Transition | | | +------------+ +-----------------+ +----------------+ | | | | +----------------------------------------------------------------+ | | | Message Handling | | | | +-----------------+ +-----------------+ +-----------------+ | | | | | Transport | | Message | | Security | | | | | | Mappings | | Processing and | | | | | | | | | | Dispatching | | | | | | | +-----------------+ +-----------------+ +-----------------+ | | | +----------------------------------------------------------------+ | | | | +----------------------------------------------------------------+ | | | PDU Handling | | | | +-----------------+ +-----------------+ +-----------------+ | | | | | Protocol | | Applications | | Access | | | | | | Operations | | | | Control | | | | | +-----------------+ +-----------------+ +-----------------+ | | | +----------------------------------------------------------------+ | | | | +----------------------------------------------------------------+ | | | Information Model | | | | +--------------+ +--------------+ +---------------+ | | | | | Structure of | | Textual | | Conformance | | | | | | Management | | Conventions | | Statements | | | | | | Information | | | | | | | | | +--------------+ +--------------+ +---------------+ | | | +----------------------------------------------------------------+ | | | | +----------------------------------------------------------------+ | | | MIBs | | | | +-------------+ +-------------+ +----------+ +----------+ | | | | | Standard v1 | | Standard v1 | | Historic | | Draft v2 | | | | | | RFC1157 | | RFC1212 | | RFC14xx | | RFC19xx | | | | | | format | | format | | format | | format | | | | | +-------------+ +-------------+ +----------+ +----------+ | | | +----------------------------------------------------------------+ | | | +--------------------------------------------------------------------+ Those marked with an asterisk (*) are expected to be written in the future. Each of these documents may be replaced or supplemented. Harrington/Wijnen Expires February 1998 [Page 15] Draft An Architecture for SNMP Management Frameworks August 1997 This Architecture document specifically describes how new documents fit into the set of documents in the area of Message and PDU handling. 2.1. Document Roadmap One or more documents may be written to describe how sets of documents taken together form specific Frameworks. The configuration of document sets might change over time, so the "roadmap" should be maintained in a document separate from the standards documents themselves. 2.2. Applicability Statement SNMP is used in networks that vary widely in size and complexity, by organizations that vary widely in their requirements of network management. Some models will be designed to address specific problems of network management, such as message security. One or more documents may be written to describe the environments to which certain versions of SNMP or models within SNMP would be appropriately applied, and those to which a given model might be inappropriately applied. 2.3. Coexistence and Transition The purpose of an evolutionary architecture is to permit new models to replace or supplement existing models. The interactions between models could result in incompatibilities, security "holes", and other undesirable effects. The purpose of Coexistence documents is to detail recognized anomalies and to describe required and recommended behaviors for resolving the interactions between models within the architecture. It would be very difficult to document all the possible interactions between a model and all other previously existing models while in the process of developing a new model. Coexistence documents are therefore expected to be prepared separately from model definition documents, to describe and resolve interaction anomalies between a model definition and one or more other model definitions. Additionally, recommendations for transitions between models may also be described, either in a coexistence document or in a separate document. Harrington/Wijnen Expires February 1998 [Page 16] Draft An Architecture for SNMP Management Frameworks August 1997 2.4. Transport Mappings SNMP messages are sent over various transports. It is the purpose of Transport Mapping documents to define how the mapping between SNMP and the transport is done. 2.5. Message Processing A Message Processing Model document defines a message format, which is typically identified by a version field in an SNMP message header. The document may also define a MIB module for use in message processing and for instrumentation of version-specific interactions. An SNMP engine includes one or more Message Processing Models, and thus may support sending and receiving multiple versions of SNMP messages. 2.6. Security Some environments require secure protocol interactions. Security is normally applied at two different stages: - in the transmission/receipt of messages, and - in the processing of the contents of messages. For purposes of this document, "security" refers to message-level security; "access control" refers to the security applied to protocol operations. Authentication, encryption, and timeliness checking are common functions of message level security. A security document describes a Security Model, the threats against which the model protects, the goals of the Security Model, the protocols which it uses to meet those goals, and it may define a MIB module to describe the data used during processing, and to allow the remote configuration of message-level security parameters, such as passwords. An SNMP engine may support multiple Security Models concurrently. 2.7. Access Control During processing, it may be required to control access to certain instrumentation for certain operations. An Access Control Model determines whether access to an object should be allowed. The mechanism by which access control is checked is defined by the Access Control Model. An Access Control Model document defines the mechanisms used to determine whether access to a managed object should be allowed, and may define a MIB module used during processing, and to allow Harrington/Wijnen Expires February 1998 [Page 17] Draft An Architecture for SNMP Management Frameworks August 1997 the remote configuration of access control policies. 2.8. Protocol Operations SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). It is the purpose of a Protocol Operations document to define the operations of the protocol with respect to the processing of the PDUs. An application document defines which Protocol Operations documents are supported by the application. 2.9. Applications An SNMP entity normally includes a number of applications. Applications use the services of an SNMP engine to accomplish specific tasks. They coordinate the processing of management information operations, and may use SNMP messages to communicate with other SNMP entities. Applications documents describe the purpose of an application, the services required of the associated SNMP engine, and the protocol operations and informational model that the application uses to perform network management operations. An application document defines which set of documents are used to specifically define the structure of management information, textual conventions, conformance requirements, and operations supported by the application. 2.10. Structure of Management Information Management information is viewed as a collection of managed objects, residing in a virtual information store, termed the Management Information Base (MIB). Collections of related objects are defined in MIB modules. It is the purpose of a Structure of Management Information document to establish the syntax for defining objects, modules, and other elements of managed information. 2.11. Textual Conventions When designing a MIB module, it is often useful to define new types similar to those defined in the SMI, but with more precise semantics, or which have special semantics associated with them. These newly defined types are termed textual conventions, and may defined in separate documents, or within a MIB module. 2.12. Conformance Statements Harrington/Wijnen Expires February 1998 [Page 18] Draft An Architecture for SNMP Management Frameworks August 1997 It may be useful to define the acceptable lower-bounds of implementation, along with the actual level of implementation achieved. It is the purpose of Conformance Statements to define the notation used for these purposes. 2.13. Management Information Base Modules MIB documents describe collections of managed objects which instrument some aspect of a managed node. 2.13.1. SNMP Instrumentation MIBs An SNMP MIB document may define a collection of managed objects which instrument the SNMP protocol itself. In addition, MIB modules may be defined within the documents which describe portions of the SNMP architecture, such as the documents for Message processing Models, Security Models, etc. for the purpose of instrumenting those Models, and for the purpose of allowing remote configuration of the Model. 2.14. SNMP Framework Documents This architecture is designed to allow an orderly evolution of portions of SNMP Frameworks. Throughout the rest of this document, the term "subsystem" refers to an abstract and incomplete specification of a portion of a Framework, that is further refined by a model specification. A "model" describes a specific design of a subsystem, defining additional constraints and rules for conformance to the model. A model is sufficiently detailed to make it possible to implement the specification. An "implementation" is an instantiation of a subsystem, conforming to one or more specific models. SNMP version 1 (SNMPv1), is the original Internet-standard Network Management Framework, as described in RFCs 1155, 1157, and 1212. SNMP version 2 (SNMPv2), is the SNMPv2 Framework as derived from the SNMPv1 Framework. It is described in RFCs 1902-1907. SNMPv2 has no message definition. Community-based SNMP version 2 (SNMPv2c), is an experimental SNMP Framework which supplements the SNMPv2 Framework, as described in RFC1901. It adds the SNMPv2c message format similar to the SNMPv1 message format. SNMP version 3 (SNMPv3), is an extensible SNMP Framework which supplements the SNMPv2 Framework, by supporting the following: - a new SNMP message format, Harrington/Wijnen Expires February 1998 [Page 19] Draft An Architecture for SNMP Management Frameworks August 1997 - Security for Messages, and - Access Control. Other SNMP Frameworks, i.e. other configurations of implemented subsystems, are expected to also be consistent with this architecture. Harrington/Wijnen Expires February 1998 [Page 20] Draft An Architecture for SNMP Management Frameworks August 1997 2.15. Operational Overview The following pictures show two communicating SNMP entities using the conceptual modularity described by this SNMP Architecture. The pictures represent SNMP entities that have traditionally been called SNMP manager and SNMP agent respectively. * One or more models may be present. (traditional SNMP manager) +--------------------------------------------------------------------+ | +--------------+ +--------------+ +--------------+ SNMP entity | | | NOTIFICATION | | NOTIFICATION | | COMMAND | | | | ORIGINATOR | | RECEIVER | | GENERATOR | | | | applications | | applications | | applications | | | +--------------+ +--------------+ +--------------+ | | ^ ^ ^ | | | | | | | v v v | | +-------+--------+-----------------+ | | ^ | | | +---------------------+ +-----------------+ | | | | Message Processing | | Security | | | Dispatcher v | Subsystem | | Subsystem | | | +-------------------+ | +------------+ | | | | | | PDU Dispatcher | | +->| v1MP * |<--->| +-------------+ | | | | | | | +------------+ | | | Other | | | | | | | | +------------+ | | | Security | | | | | | | +->| v2cMP * |<--->| | Model | | | | | Message | | | +------------+ | | +-------------+ | | | | Dispatcher <--------->+ | | | | | | | | | +------------+ | | +-------------+ | | | | | | +->| v3MP * |<--->| | User-based | | | | | Transport | | | +------------+ | | | Security | | | | | Mapping | | | +------------+ | | | Model | | | | | (e.g RFC1906) | | +->| otherMP * |<--->| +-------------+ | | | +-------------------+ | +------------+ | | | | | ^ +---------------------+ +-----------------+ | | | | | v | +--------------------------------------------------------------------+ +-----+ +-----+ +-------+ | UDP | | IPX | . . . | other | +-----+ +-----+ +-------+ ^ ^ ^ | | | v v v +------------------------------+ | Network | +------------------------------+ Harrington/Wijnen Expires February 1998 [Page 21] Draft An Architecture for SNMP Management Frameworks August 1997 +------------------------------+ | Network | +------------------------------+ ^ ^ ^ | | | v v v +-----+ +-----+ +-------+ | UDP | | IPX | . . . | other | +-----+ +-----+ +-------+ (traditional SNMP agent) +--------------------------------------------------------------------+ | ^ | | | +---------------------+ +-----------------+ | | | | Message Processing | | Security | | | Dispatcher v | Subsystem | | Subsystem | | | +-------------------+ | +------------+ | | | | | | Transport | | +->| v1MP * |<--->| +-------------+ | | | | Mapping | | | +------------+ | | | Other | | | | | (e.g. RFC1906) | | | +------------+ | | | Security | | | | | | | +->| v2cMP * |<--->| | Model | | | | | Message | | | +------------+ | | +-------------+ | | | | Dispatcher <--------->+ | | | | | | | | | +------------+ | | +-------------+ | | | | | | +->| v3MP * |<--->| | User-based | | | | | | | | +------------+ | | | Security | | | | | | | | +------------+ | | | Model | | | | | PDU Dispatcher | | +->| otherMP * |<--->| +-------------+ | | | +-------------------+ | +------------+ | | | | | ^ +---------------------+ +-----------------+ | | | | | v | | +-------+-------------------------+----------------+ | | ^ ^ ^ | | | | | | | v v v | | +-------------+ +---------+ +--------------+ +-------------+ | | | COMMAND | | ACCESS | | NOTIFICATION | | PROXY * | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | application | | | | applications | | application | | | +-------------+ +---------+ +--------------+ +-------------+ | | ^ ^ | | | | | | v v | | +----------------------------------------------+ | | | MIB instrumentation | SNMP entity | +--------------------------------------------------------------------+ Harrington/Wijnen Expires February 1998 [Page 22] Draft An Architecture for SNMP Management Frameworks August 1997 3. Elements of the Architecture This section describes the various elements of the architecture and how they are named. There are three kinds of naming: 1) the naming of entities, 2) the naming of identities, and 3) the naming of management information. This architecture also defines some names for other constructs that are used in the documentation. 3.1. The Naming of Entities The following picture shows detail about an SNMP entity and how components within it are named. +--------------------------------------------------------------------+ | SNMP entity | | | | +--------------------------------------------------------------+ | | | SNMP engine (identified by snmpEngineID) | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | | | | | | | | | | | Dispatcher | | Message | | Security | | Access | | | | | | | | Processing | | Subsystem | | Control | | | | | | | | Subsystem | | | | Subsystem | | | | | | | | | | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | +--------------------------------------------------------------+ | | | | +--------------------------------------------------------------+ | | | Application(s) | | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | Command | | Notification | | Proxy | | | | | | Generator | | Receiver | | Forwarder | | | | | +-------------+ +--------------+ +--------------+ | | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | Command | | Notification | | Other | | | | | | Responder | | Originator | | | | | | | +-------------+ +--------------+ +--------------+ | | | | | | | +--------------------------------------------------------------+ | | | +--------------------------------------------------------------------+ Harrington/Wijnen Expires February 1998 [Page 23] Draft An Architecture for SNMP Management Frameworks August 1997 3.1.1. SNMP entity An SNMP entity is an implementation of this architecture. Each such SNMP entity consists of an SNMP engine and one or more associated applications. 3.1.2. SNMP engine An SNMP engine provides services for sending and receiving messages, authenticating and encrypting messages, and controlling access to managed objects. There is a one-to-one association between an SNMP engine and the SNMP entity which contains it. The engine contains: 1) a Dispatcher, 2) a Message Processing Subsystem, 3) a Security Subsystem, and 4) an Access Control Subsystem. 3.1.3. snmpEngineID Within an administrative domain, an snmpEngineID is the unique and unambiguous identifier of an SNMP engine. Since there is a one-to-one association between SNMP engines and SNMP entities, it also uniquely and unambiguously identifies the SNMP entity. 3.1.4. Dispatcher There is only one Dispatcher in an SNMP engine. It allows for concurrent support of multiple versions of SNMP messages in the SNMP engine. It does so by: - sending and receiving SNMP messages to/from the network, - determining the version of an SNMP message and interact with the corresponding Message Processing Model, - providing an abstract interface to SNMP applications for dispatching a PDU to an application. - providing an abstract interface for SNMP applications that allows them to send a PDU to a remote SNMP entity. Harrington/Wijnen Expires February 1998 [Page 24] Draft An Architecture for SNMP Management Frameworks August 1997 3.1.5. Message Processing Subsystem The Message Processing Subsystem is responsible for preparing messages for sending, and extracting data from received messages. The Message Processing Subsystem potentially contains multiple Message Processing Models as shown in the next picture. * One or more Message Processing Models may be present. +------------------------------------------------------------------+ | | | Message Processing Subsystem | | | | +------------+ +------------+ +------------+ +------------+ | | | * | | * | | * | | * | | | | SNMPv3 | | SNMPv1 | | SNMPv2c | | Other | | | | Message | | Message | | Message | | Message | | | | Processing | | Processing | | Processing | | Processing | | | | Model | | Model | | Model | | Model | | | | | | | | | | | | | +------------+ +------------+ +------------+ +------------+ | | | +------------------------------------------------------------------+ 3.1.6. Message Processing Model Each Message Processing Model defines the format of a particular version of an SNMP message and coordinates the preparation and extraction of each such version-specific messages. Harrington/Wijnen Expires February 1998 [Page 25] Draft An Architecture for SNMP Management Frameworks August 1997 3.1.7. Security Subsystem The Security Subsystem provides security services such as the authentication and privacy of messages and potentially contains multiple Security Models as shown in the next picture. * One or more Security Models may be present. +------------------------------------------------------------------+ | | | Security Subsystem | | | | +----------------+ +-----------------+ +-------------------+ | | | * | | * | | * | | | | User-Based | | Other | | Other | | | | Security | | Security | | Security | | | | Model | | Model | | Model | | | | | | | | | | | +----------------+ +-----------------+ +-------------------+ | | | +------------------------------------------------------------------+ 3.1.8. Security Model A Security Model defines the threats against which it protects, the goals of its services, and the security protocols used to provide security services such as authentication and privacy. 3.1.9. Security Protocol A Security Protocol defines the mechanisms, procedures, and MIB data used to provide a security service such as authentication or privacy. Harrington/Wijnen Expires February 1998 [Page 26] Draft An Architecture for SNMP Management Frameworks August 1997 3.1.10. Access Control Subsystem The Access Control Subsystem provides authorization services by means of one or more Access Control Models. +------------------------------------------------------------------+ | | | Access Control Subsystem | | | | +---------------+ +-----------------+ +------------------+ | | | * | | * | | * | | | | View-Based | | Other | | Other | | | | Access | | Access | | Access | | | | Control | | Control | | Control | | | | Model | | Model | | Model | | | | | | | | | | | +---------------+ +-----------------+ +------------------+ | | | +------------------------------------------------------------------+ 3.1.11. Access Control Model An Access Control Model defines a particular access decision function in order to support decisions regarding access rights. Harrington/Wijnen Expires February 1998 [Page 27] Draft An Architecture for SNMP Management Frameworks August 1997 3.1.12. Applications There are several types of applications, including: - command generators, which monitor and manipulate management data, - command responders, which provide access to management data, - notification originators, which initiate asynchronous messages, - notification receivers, which process asynchronous messages, and - proxy forwarders, which forward messages between entities. These applications make use of the services provided by the SNMP engine. 3.1.13. SNMP Agent An SNMP entity containing one or more command responder and/or notification originator applications (along with their associated SNMP engine) has traditionally been called an SNMP agent. 3.1.14. SNMP Manager An SNMP entity containing one or more command generator and/or notification receiver applications (along with their associated SNMP engine) has traditionally been called an SNMP manager. Harrington/Wijnen Expires February 1998 [Page 28] Draft An Architecture for SNMP Management Frameworks August 1997 3.2. The Naming of Identities principal <---------------------------------+ | +-------------------------------------|-----+ | SNMP engine | | | | | | +-----------------------+ | | | | Security Model | | | | | +-------------+ | | | wire | | | Model | +------------+--+ | <----------->| Dependent |<-->| | securityName| | | | | Security ID | +---------------+ | | | +-------------+ | | | | | | | +-----------------------+ | | | | | +-------------------------------------------+ 3.2.1. Principal A principal is the "who" on whose behalf services are provided or processing takes place. A principal can be, among other things, an individual acting in a particular role; a set of individuals, with each acting in a particular role; an application; or a set of applications; and combinations thereof. 3.2.2. securityName A securityName is a human readable string representing a principal. It has a model independent format, and can be used outside a particular Security Model. 3.2.3. Model dependent security ID A model dependent security ID is the model specific representation of a securityName within a particular Security Model. Model dependent security IDs may or may not be human readable, and have a model dependent syntax. Examples include community names, user names, and parties. The transformation of model dependent security IDs into securityNames and vice versa is the responsibility of the relevant Security Model. Harrington/Wijnen Expires February 1998 [Page 29] Draft An Architecture for SNMP Management Frameworks August 1997 3.3. The Naming of Management Information Management information resides at an SNMP entity where a Command Responder Application has local access to potentially multiple contexts. Such a Command Responder application uses a contextEngineID equal to the snmpEngineID of its associated SNMP engine. +-----------------------------------------------------------------+ | SNMP entity (identified by snmpEngineID, example: abcd) | | | | +------------------------------------------------------------+ | | | SNMP engine (identified by snmpEngineID) | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | | | | | | | | | | | Dispatcher | | Message | | Security | | Access | | | | | | | | Processing | | Subsystem | | Control | | | | | | | | Subsystem | | | | Subsystem | | | | | | | | | | | | | | | | | +-------------+ +------------+ +-----------+ +-----------+ | | | | | | | +------------------------------------------------------------+ | | | | +------------------------------------------------------------+ | | | Command Responder Application | | | | (contextEngineID, example: abcd) | | | | | | | | example contextNames: | | | | | | | | "bridge1" "bridge2" "" (default) | | | | --------- --------- ------------ | | | | | | | | | | +------|------------------|-------------------|--------------+ | | | | | | | +------|------------------|-------------------|--------------+ | | | MIB | instrumentation | | | | | | +---v------------+ +---v------------+ +----v-----------+ | | | | | context | | context | | context | | | | | | | | | | | | | | | | +------------+ | | +------------+ | | +------------+ | | | | | | | bridge MIB | | | | bridge MIB | | | | other MIB | | | | | | | +------------+ | | +------------+ | | +------------+ | | | | | | | | | | | | | | | | | | | | +------------+ | | | | | | | | | | | some MIB | | | | | | | | | | | +------------+ | | | | | | | | | | | | | +-----------------------------------------------------------------+ Harrington/Wijnen Expires February 1998 [Page 30] Draft An Architecture for SNMP Management Frameworks August 1997 3.3.1. An SNMP Context An SNMP context, or just "context" for short, is a collection of management information accessible by an SNMP entity. An item of management information may exist in more than one context. An SNMP engine potentially has access to many contexts. Typically, there are many instances of each managed object type within a management domain. For simplicity, the method for identifying instances specified by the MIB module does not allow each instance to be distinguished amongst the set of all instances within a management domain; rather, it allows each instance to be identified only within some scope or "context", where there are multiple such contexts within the management domain. Often, a context is a physical device, or perhaps, a logical device, although a context can also encompass multiple devices, or a subset of a single device, or even a subset of multiple devices, but a context is always defined as a subset of a single SNMP entity. Thus, in order to identify an individual item of management information within the management domain, its contextName and contextEngineID must be identified in addition to its object type and its instance. For example, the managed object type ifDescr [RFC1573], is defined as the description of a network interface. To identify the description of device-X's first network interface, four pieces of information are needed: the snmpEngineID of the SNMP entity which provides access to the management information at device-X, the contextName (device-X), the managed object type (ifDescr), and the instance ("1"). Each context has (at least) one unique identification within the management domain. The same item of management information can exist in multiple contexts. So, an item of management information can have multiple unique identifications, either because it exists in multiple contexts, and/or because each such context has multiple unique identifications. The combination of a contextEngineID and a contextName unambiguously identifies a context within an administrative domain. 3.3.2. contextEngineID Within an administrative domain, a contextEngineID uniquely identifies an SNMP entity that may realize an instance of a context with a particular contextName. 3.3.3. contextName A contextName is used to name a context. Each contextName MUST be unique within an SNMP entity. Harrington/Wijnen Expires February 1998 [Page 31] Draft An Architecture for SNMP Management Frameworks August 1997 3.3.4. scopedPDU A scopedPDU is a block of data containing a contextEngineID, a contextName, and a PDU. The PDU is an SNMP Protocol Data Unit containing information named in the context which is unambiguously identified within an administrative domain by the combination of the contextEngineID and the contextName. See, for example, RFC1905 for more information about SNMP PDUs. 3.4. Other Constructs 3.4.1. maxSizeResponseScopedPDU The maxSizeResponseScopedPDU is the maximum size of a scopedPDU to be included in a response message, making allowance for the message header. 3.4.2. Local Configuration Datastore The subsystems, models, and applications within an SNMP entity may need to retain their own sets of configuration information. Portions of the configuration information may be accessible as managed objects. The collection of these sets of information is referred to as an entity's Local Configuration Datastore (LCD). 3.4.3. securityLevel This architecture recognizes three levels of security: - without authentication and without privacy (noAuthNoPriv) - with authentication but without privacy (authNoPriv) - with authentication and with privacy (authPriv) These three values are ordered such that noAuthNoPriv is less than authNoPriv and authNoPriv is less than authPriv. Every message has an associated securityLevel. All Subsystems (Message Processing, Security, Access Control) and applications are required to either supply a value of securityLevel or to abide by the supplied value of securityLevel while processing the message and its contents. Harrington/Wijnen Expires February 1998 [Page 32] Draft An Architecture for SNMP Management Frameworks August 1997 4. Abstract Service Interfaces. Abstract service interfaces have been defined to describe the conceptual interfaces between the various subsystems within an SNMP entity. These abstract service interfaces are defined by a set of primitives that define the services provided and the abstract data elements that are to be passed when the services are invoked. This section lists the primitives that have been defined for the various subsystems. 4.1. Common Primitives These primitive(s) are provided by multiple Subsystems. 4.1.1. Release State Reference Information All Subsystems which pass stateReference information also provide a primitive to release the memory that holds the referenced state information: stateRelease( IN stateReference -- handle of reference to be released ) 4.2. Dispatcher Primitives The Dispatcher typically provides services to the SNMP applications via its PDU Dispatcher. This section describes the primitives provided by the PDU Dispatcher. 4.2.1. Generate Outgoing Request or Notification The PDU Dispatcher provides the following primitive for an application to send an SNMP Request or Notification to another SNMP entity: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- transport address to be used IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) Harrington/Wijnen Expires February 1998 [Page 33] Draft An Architecture for SNMP Management Frameworks August 1997 4.2.2. Process Incoming Request or Notification PDU The PDU Dispatcher provides the following primitive to pass an incoming SNMP PDU to an application: processPdu( -- process Request/Notification PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information ) -- needed when sending a response 4.2.3. Generate Outgoing Response The PDU Dispatcher provides the following primitive for an application to return an SNMP Response PDU to the PDU Dispatcher: returnResponsePdu( IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication ) -- error counter OID/value if error 4.2.4. Process Incoming Response PDU The PDU Dispatcher provides the following primitive to pass an incoming SNMP Response PDU to an application: processResponsePdu( -- process Response PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context Harrington/Wijnen Expires February 1998 [Page 34] Draft An Architecture for SNMP Management Frameworks August 1997 IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN statusInformation -- success or errorIndication IN sendPduHandle -- handle from sendPDU ) 4.2.5. Registering Responsibility for Handling SNMP PDUs. Applications can register/unregister responsibility for a specific contextEngineID, for specific pduTypes, with the PDU Dispatcher according to these primitives: statusInformation = -- success or errorIndication registerContextEngineID( IN contextEngineID -- take responsibility for this one IN pduType -- the pduType(s) to be registered ) unregisterContextEngineID( IN contextEngineID -- give up responsibility for this one IN pduType -- the pduType(s) to be unregistered ) 4.3. Message Processing Subsystem Primitives The Dispatcher interacts with a Message Processing Model to process a specific version of an SNMP Message. This section describes the primitives provided by the Message Processing Subsystem. 4.3.1. Prepare an Outgoing SNMP Request or Notification Message The Message Processing Subsystem provides this service primitive for preparing an outgoing SNMP Request or Notification Message: statusInformation = -- success or errorIndication prepareOutgoingMessage( IN transportDomain -- transport domain to be used IN transportAddress -- transport address to be used IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE IN sendPduHandle -- the handle for matching -- incoming responses OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address Harrington/Wijnen Expires February 1998 [Page 35] Draft An Architecture for SNMP Management Frameworks August 1997 OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- its length ) 4.3.2. Prepare an Outgoing SNMP Response Message The Message Processing Subsystem provides this service primitive for preparing an outgoing SNMP Response Message: result = -- SUCCESS or FAILURE prepareResponseMessage( IN messageProcessingModel -- typically, SNMP version IN securityModel -- same as on incoming request IN securityName -- same as on incoming request IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication -- error counter OID/value if error OUT destTransportDomain -- destination transport domain OUT destTransportAddress -- destination transport address OUT outgoingMessage -- the message to send OUT outgoingMessageLength -- its length ) 4.3.3. Prepare Data Elements from an Incoming SNMP Message The Message Processing Subsystem provides this service primitive for preparing the abstract data elements from an incoming SNMP message: result = -- SUCCESS or errorIndication prepareDataElements( IN transportDomain -- origin transport domain IN transportAddress -- origin transport address IN wholeMsg -- as received from the network IN wholeMsglength -- as received from the network OUT messageProcessingModel -- typically, SNMP version OUT securityModel -- Security Model to use OUT securityName -- on behalf of this principal OUT securityLevel -- Level of Security requested OUT contextEngineID -- data from/at this entity OUT contextName -- data from/in this context OUT pduVersion -- the version of the PDU OUT PDU -- SNMP Protocol Data Unit OUT pduType -- SNMP PDU type OUT sendPduHandle -- handle for matched request Harrington/Wijnen Expires February 1998 [Page 36] Draft An Architecture for SNMP Management Frameworks August 1997 OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU OUT statusInformation -- success or errorIndication -- error counter OID/value if error OUT stateReference -- reference to state information -- to be used for a possible Response ) 4.4. Access Control Subsystem Primitives Applications are the typical clients of the service(s) of the Access Control Subsystem. The following primitive is provided by the Access Control Subsystem to check if access is allowed: statusInformation = -- success or errorIndication isAccessAllowed( IN securityModel -- Security Model in use IN securityName -- principal who wants to access IN securityLevel -- Level of Security IN viewType -- read, write, or notify view IN contextName -- context containing variableName IN variableName -- OID for the managed object ) 4.5. Security Subsystem Primitives The Message Processing Subsystem is the typical client of the services of the Security Subsystem. 4.5.1. Generate a Request or Notification Message The Security Subsystem provides the following primitive to generate a Request or Notification message: statusInformation = generateRequestMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of the generated message ) 4.5.2. Process Incoming Message Harrington/Wijnen Expires February 1998 [Page 37] Draft An Architecture for SNMP Management Frameworks August 1997 The Security Subsystem provides the following primitive to process an incoming message: statusInformation = -- errorIndication or success -- error counter OID/value if error processIncomingMsg( IN messageProcessingModel -- typically, SNMP version IN maxMessageSize -- of the sending SNMP entity IN securityParameters -- for the received message IN securityModel -- for the received message IN securityLevel -- Level of Security IN wholeMsg -- as received on the wire IN wholeMsgLength -- length as received on the wire OUT securityEngineID -- identification of the principal OUT securityName -- identification of the principal OUT scopedPDU, -- message (plaintext) payload OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU OUT securityStateReference -- reference to security state ) -- information, needed for response 4.5.3. Generate a Response Message The Security Subsystem provides the following primitive to generate a Response message: statusInformation = generateResponseMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- for the outgoing message IN scopedPDU -- message (plaintext) payload IN securityStateReference -- reference to security state -- information from original request OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of the generated message ) 4.6. User Based Security Model Internal Primitives 4.6.1. User-based Security Model Primitives for Authentication The User-based Security Model provides the following internal primitives to pass data back and forth between the Security Model itself and the authentication service: Harrington/Wijnen Expires February 1998 [Page 38] Draft An Architecture for SNMP Management Frameworks August 1997 statusInformation = authenticateOutgoingMsg( IN authKey -- secret key for authentication IN wholeMsg -- unauthenticated complete message OUT authenticatedWholeMsg -- complete authenticated message ) statusInformation = authenticateIncomingMsg( IN authKey -- secret key for authentication IN authParameters -- as received on the wire IN wholeMsg -- as received on the wire OUT authenticatedWholeMsg -- complete authenticated message ) 4.6.2. User-based Security Model Primitives for Privacy The User-based Security Model provides the following internal primitives to pass data back and forth between the Security Model itself and the privacy service: statusInformation = encryptData( IN encryptKey -- secret key for encryption IN dataToEncrypt -- data to encrypt (scopedPDU) OUT encryptedData -- encrypted data (encryptedPDU) OUT privParameters -- filled in by service provider ) statusInformation = decryptData( IN decryptKey -- secret key for decrypting IN privParameters -- as received on the wire IN encryptedData -- encrypted data (encryptedPDU) OUT decryptedData -- decrypted data (scopedPDU) ) Harrington/Wijnen Expires February 1998 [Page 39] Draft An Architecture for SNMP Management Frameworks August 1997 4.7. Scenario Diagrams 4.7.1. Command Generator or Notification Originator Application This diagram shows how a Command Generator or Notification Originator application requests that a PDU be sent, and how the response is returned (asynchronously) to that application. Command Dispatcher Message Security Generator | Processing Model | | Model | | | | | | sendPdu | | | |------------------->| | | | | prepareOutgoingMessage | | : |------------------------->| | : | | generateRequestMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<-------------------------| | : | | | : |------------------+ | | : | Send SNMP | | | : | Request Message | | | : | to Network | | | : | v | | : : : : : : : : : : : : : : : : | | | | : | | | | : | Receive SNMP | | | : | Response Message | | | : | from Network | | | : |<-----------------+ | | : | | | : | prepareDataElements | | : |------------------------->| | : | | processIncomingMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<-------------------------| | | processResponsePdu | | | |<-------------------| | | | | | | Harrington/Wijnen Expires February 1998 [Page 40] Draft An Architecture for SNMP Management Frameworks August 1997 4.7.2. Scenario Diagram for a Command Responder Application This diagram shows how a Command Responder or Notification Receiver application registers for handling a pduType, how a PDU is dispatched to the application after a SNMP message is received, and how the Response is (asynchronously) send back to the network. Command Dispatcher Message Security Responder | Processing Model | | Model | | | | | | registerContextEngineID | | | |------------------------>| | | |<------------------------| | | | | | Receive SNMP | | | : | Message | | | : | from Network | | | : |<-------------+ | | : | | | : | prepareDataElements | | : |-------------------->| | : | | processIncomingMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<--------------------| | | processPdu | | | |<------------------------| | | | | | | : : : : : : : : | returnResponsePdu | | | |------------------------>| | | : | prepareResponseMsg | | : |-------------------->| | : | | generateResponseMsg | : | |-------------------->| : | | | : | |<--------------------| : | | | : |<--------------------| | : | | | : |--------------+ | | : | Send SNMP | | | : | Message | | | : | to Network | | | : | v | | Harrington/Wijnen Expires February 1998 [Page 41] Draft An Architecture for SNMP Management Frameworks August 1997 5. Definition of Managed Objects for SNMP Management Frameworks SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY, snmpModules, Unsigned32, Integer32 FROM SNMPv2-SMI TEXTUAL-CONVENTION FROM SNMPv2-TC MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpFrameworkMIB MODULE-IDENTITY LAST-UPDATED "9707260000Z" -- 26 July 1997, midnight ORGANIZATION "SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@tis.com Subscribe: majordomo@tis.com In message body: subscribe snmpv3 Chair: Russ Mundy Trusted Information Systems postal: 3060 Washington Rd Glenwood MD 21738 USA email: mundy@tis.com phone: +1-301-854-6889 Co-editor Dave Harrington Cabletron Systems, Inc postal: Post Office Box 5005 MailStop: Durham 35 Industrial Way Rochester NH 03867-5005 USA email: dbh@cabletron.com phone: +1-603-337-7357 Co-editor: Bert Wijnen IBM T.J. Watson Research postal: Schagen 33 3461 GL Linschoten Netherlands email: wijnen@vnet.ibm.com phone: +31-348-432-794 " DESCRIPTION "The SNMP Management Architecture MIB" ::= { snmpModules 7 } -- DBH: check if this number is indeed OK -- Textual Conventions used in the SNMP Management Architecture *** SnmpEngineID ::= TEXTUAL-CONVENTION STATUS current Harrington/Wijnen Expires February 1998 [Page 42] Draft An Architecture for SNMP Management Frameworks August 1997 DESCRIPTION "An SNMP engine's administratively-unique identifier. The value for this object may not be all zeros or all 'ff'H or the empty (zero length) string. The initial value for this object may be configured via an operator console entry or via an algorithmic function. In the latter case, the following example algorithm is recommended. 1) The very first bit is used to indicate how the rest of the data is composed. 0 - as defined by enterprise using former methods that existed before SNMPv3. See item 2 below. 1 - as defined by this architecture, see item 3 below. Note that this allows existing uses of the engineID (also known as AgentID [RFC1910]) to co-exist with any new uses. 2) The snmpEngineID has a length of 12 octets. The first four octets are set to the binary equivalent of the agent's SNMP network management private enterprise number as assigned by the Internet Assigned Numbers Authority (IANA). For example, if Acme Networks has been assigned { enterprises 696 }, the first four octets would be assigned '000002b8'H. The remaining eight octets are determined via one or more enterprise specific methods. Such methods must be designed so as to maximize the possibility that the value of this object will be unique in the agent's administrative domain. For example, it may be the IP address of the SNMP entity, or the MAC address of one of the interfaces, with each address suitably padded with random octets. If multiple methods are defined, then it is recommended that the first octet indicate the method being used and the remaining octets be a function of the method. 3) The length of the octet strings varies. The first four octets are set to the binary equivalent of the agent's SNMP network management private enterprise number as assigned by the Harrington/Wijnen Expires February 1998 [Page 43] Draft An Architecture for SNMP Management Frameworks August 1997 Internet Assigned Numbers Authority (IANA). For example, if Acme Networks has been assigned { enterprises 696 }, the first four octets would be assigned '000002b8'H. The very first bit is set to 1. For example, the above value for Acme Networks now changes to be '800002b8'H. The fifth octet indicates how the rest (6th and following octets) are formatted. The values for the fifth octet are: 0 - reserved, unused. 1 - IPv4 address (4 octets) lowest non-special IP address 2 - IPv6 address (16 octets) lowest non-special IP address 3 - MAC address (6 octets) lowest IEEE MAC address, canonical order 4 - Text, administratively assigned Maximum remaining length 27 5 - Octets, administratively assigned Maximum remaining length 27 6-127 - reserved, unused 127-255 - as defined by the enterprise Maximum remaining length 27 " SYNTAX OCTET STRING (SIZE(1..32)) SnmpSecurityModel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identifier that uniquely identifies a securityModel of the Security Subsystem within the SNMP Management Architecture. The values for securityModel are allocated as follows: - The zero value is reserved. - Values between 1 and 255, inclusive, are reserved for standards-track Security Models and are managed by the Internet Assigned Numbers Authority (IANA). - Values greater than 255 are allocated to enterprise specific Security Models. An enterprise specific Harrington/Wijnen Expires February 1998 [Page 44] Draft An Architecture for SNMP Management Frameworks August 1997 securityModel value is defined to be: enterpriseID * 256 + security model within enterprise For example, the fourth Security Model defined by the enterprise whose enterpriseID is 1 would be 260. The eight bits allow a maximum of 255 (256-1 reserved) standards based Security Models. Similarly, they allow a maximum of 255 Security Models per enterprise. It is believed that the assignment of new securityModel values will be rare in practice because the larger the number of simultaneously utilized Security Models, the larger the chance that interoperability will suffer. Consequently, it is believed that such a range will be sufficient. In the unlikely event that the standards committee finds this number to be insufficient over time, an enterprise number can be allocated to obtain an additional 255 possible values. Note that the most significant bit must be zero; hence, there are 23 bits allocated for various organizations to design and define non-standard securityModels. This limits the ability to define new proprietary implementations of Security Models to the first 8,388,608 enterprises. It is worthwhile to note that, in its encoded form, the securityModel value will normally require only a single byte since, in practice, the leftmost bits will be zero for most messages and sign extension is suppressed by the encoding rules. As of this writing, there are several values of securityModel defined for use with SNMP or reserved for use with supporting MIB objects. They are as follows: 0 reserved for 'none' 1 reserved for SNMPv1 2 reserved for SNMPv2c 3 User-Base Security Model (USM) 255 reserved for 'any' " SYNTAX INTEGER(0..2147483647) SnmpMessageProcessingModel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identifier that uniquely identifies a Message Harrington/Wijnen Expires February 1998 [Page 45] Draft An Architecture for SNMP Management Frameworks August 1997 Processing Model of the Message Processing Subsystem within a SNMP Management Architecture. The values for messageProcessingModel are allocated as follows: - Values between 0 and 255, inclusive, are reserved for standards-track Message Processing Models and are managed by the Internet Assigned Numbers Authority (IANA). - Values greater than 255 are allocated to enterprise specific Message Processing Models. An enterprise messageProcessingModel value is defined to be: enterpriseID * 256 + messageProcessingModel within enterprise For example, the fourth Message Processing Model defined by the enterprise whose enterpriseID is 1 would be 260. The eight bits allow a maximum of 256 standards based Message Processing Models. Similarly, they allow a maximum 256 Message Processing Models per enterprise. It is believed that the assignment of new messageProcessingModel values will be rare in practice because the larger the number of simultaneously utilized Message Processing Models, the larger the chance that interoperability will suffer. It is believed that such a range will be sufficient. In the unlikely event that the standards committee finds this number to be insufficient over time, an enterprise number can be allocated to obtain an additional 256 possible values. Note that the most significant bit must be zero; hence, there are 23 bits allocated for various organizations to design and define non-standard messageProcessingModels. This limits the ability to define new proprietary implementations of Message Processing Models to the first 8,388,608 enterprises. It is worthwhile to note that, in its encoded form, the securityModel value will normally require only a single byte since, in practice, the leftmost bits will be zero for most messages and sign extension is suppressed by the encoding rules. As of this writing, there are several values of messageProcessingModel defined for use with SNMP. Harrington/Wijnen Expires February 1998 [Page 46] Draft An Architecture for SNMP Management Frameworks August 1997 They are as follows: 0 reserved for SNMPv1 1 reserved for SNMPv2c 2 reserved for SNMPv2u 3 reserved for SNMPv3 " SYNTAX INTEGER(0..2147483647) SnmpSecurityLevel ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A Level of Security at which SNMP messages can be sent or with which operations are being processed; in particular, one of: noAuthNoPriv - without authentication and without privacy, authNoPriv - with authentication but without privacy, authPriv - with authentication and with privacy. These three values are ordered such that noAuthNoPriv is less than authNoPriv and authNoPriv is less than authPriv. " SYNTAX INTEGER { noAuthNoPriv(1), authNoPriv(2), authPriv(3) } SnmpAdminString ::= TEXTUAL-CONVENTION DISPLAY-HINT "255a" STATUS current DESCRIPTION "An octet string containing administrative information, preferably in human-readable form. To facilitate internationalization, this information is represented using the ISO/IEC IS 10646-1 character set, encoded as an octet string using the UTF-8 character encoding scheme described in RFC 2044. Since additional code points are added by amendments to the 10646 standard from time to time, implementations must be prepared to encounter any code point from 0x00000000 to 0x7fffffff. The use of control codes should be avoided. For code points not directly supported by user interface hardware or software, an alternative means Harrington/Wijnen Expires February 1998 [Page 47] Draft An Architecture for SNMP Management Frameworks August 1997 of entry and display, such as hexadecimal, may be provided. For information encoded in 7-bit US-ASCII, the UTF-8 representation is identical to the US-ASCII encoding. Note that when this TC is used for an object that is used or envisioned to be used as an index, then a SIZE restriction must be specified so that the number sub-identifiers for any object instance do not exceed the limit of 128, as defined by [RFC1905]. " SYNTAX OCTET STRING (SIZE (0..255)) -- Administrative assignments **************************************** snmpFrameworkAdmin OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 } snmpFrameworkMIBObjects OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 } snmpFrameworkMIBConformance OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 } -- the snmpEngine Group ********************************************** snmpEngine OBJECT IDENTIFIER ::= { snmpFrameworkMIBObjects 1 } snmpEngineID OBJECT-TYPE SYNTAX SnmpEngineID MAX-ACCESS read-only STATUS current DESCRIPTION "An SNMP engine's administratively-unique identifier. " ::= { snmpEngine 1 } snmpEngineBoots OBJECT-TYPE SYNTAX Unsigned32 -- (1..4294967295) MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times that the SNMP engine has (re-)initialized itself since its initial configuration. " ::= { snmpEngine 2 } snmpEngineTime OBJECT-TYPE SYNTAX Integer32 (0..2147483647) MAX-ACCESS read-only STATUS current DESCRIPTION "The number of seconds since the SNMP engine last incremented the snmpEngineBoots object. " ::= { snmpEngine 3 } Harrington/Wijnen Expires February 1998 [Page 48] Draft An Architecture for SNMP Management Frameworks August 1997 -- Registration Points for Authentication and Privacy Protocols ** snmpAuthProtocols OBJECT-IDENTITY STATUS current DESCRIPTION "Registration point for standards-track authentication protocols used in SNMP Management Frameworks. " ::= { snmpFrameworkAdmin 1 } snmpPrivProtocols OBJECT-IDENTITY STATUS current DESCRIPTION "Registration point for standards-track privacy protocols used in SNMP Management Frameworks. " ::= { snmpFrameworkAdmin 2 } -- Conformance information ******************************************* snmpFrameworkMIBCompliances OBJECT IDENTIFIER ::= { snmpFrameworkMIBConformance 1 } snmpFrameworkMIBGroups OBJECT IDENTIFIER ::= { snmpFrameworkMIBConformance 2 } -- compliance statements snmpFrameworkMIBCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP engines which implement the SNMP Management Framework MIB. " MODULE -- this module MANDATORY-GROUPS { snmpEngineGroup } ::= { snmpFrameworkMIBCompliances 1 } -- units of conformance snmpEngineGroup OBJECT-GROUP OBJECTS { snmpEngineID, snmpEngineBoots, snmpEngineTime } STATUS current DESCRIPTION "A collection of objects for identifying and determining the configuration and current timeliness values of an SNMP engine. " ::= { snmpFrameworkMIBGroups 1 } Harrington/Wijnen Expires February 1998 [Page 49] Draft An Architecture for SNMP Management Frameworks August 1997 END Harrington/Wijnen Expires February 1998 [Page 50] Draft An Architecture for SNMP Management Frameworks August 1997 6. Security Considerations This document describes how an implementation can include a Security Model to protect network management messages and an Access Control Model to control access to management information. The level of security provided is determined by the specific Security Model implementation(s) and the specific Access Control Model implementation(s) used. Applications have access to data which is not secured. Applications should take reasonable steps to protect the data from disclosure. It is the responsibility of the purchaser of an implementation to ensure that: 1) an implementation complies with the rules defined by this architecture, 2) the Security and Access Control Models utilized satisfy the security and access control needs of the organization, 3) the implementations of the Models and Applications comply with the model and application specifications, 4) and the implementation protects configuration secrets from inadvertent disclosure. Harrington/Wijnen Expires February 1998 [Page 51] Draft An Architecture for SNMP Management Frameworks August 1997 7. Editor's Addresses Co-editor: Bert Wijnen IBM T.J. Watson Research postal: Schagen 33 3461 GL Linschoten Netherlands email: wijnen@vnet.ibm.com phone: +31-348-432-794 Co-editor Dave Harrington Cabletron Systems, Inc postal: Post Office Box 5005 MailStop: Durham 35 Industrial Way Rochester NH 03867-5005 USA email: dbh@cabletron.com phone: +1-603-337-7357 Harrington/Wijnen Expires February 1998 [Page 52] Draft An Architecture for SNMP Management Frameworks August 1997 8. Acknowledgements This document is the result of the efforts of the SNMPv3 Working Group. Some special thanks are in order to the following SNMPv3 WG members: Dave Battle (SNMP Research, Inc.) Uri Blumenthal (IBM T.J. Watson Research Center) Jeff Case (SNMP Research, Inc.) John Curran (BBN) T. Max Devlin (Hi-TECH Connections) John Flick (Hewlett Packard) David Harrington (Cabletron Systems Inc.) N.C. Hien (IBM T.J. Watson Research Center) Dave Levi (SNMP Research, Inc.) Louis A Mamakos (UUNET Technologies Inc.) Paul Meyer (Secure Computing Corporation) Keith McCloghrie (Cisco Systems) Russ Mundy (Trusted Information Systems, Inc.) Bob Natale (ACE*COMM Corporation) Mike O'Dell (UUNET Technologies Inc.) Dave Perkins (DeskTalk) Peter Polkinghorne (Brunel University) Randy Presuhn (BMC Software, Inc.) David Reid (SNMP Research, Inc.) Shawn Routhier (Epilogue) Juergen Schoenwaelder (TU Braunschweig) Bob Stewart (Cisco Systems) Bert Wijnen (IBM T.J. Watson Research Center) The document is based on recommendations of the IETF Security and Administrative Framework Evolution for SNMP Advisory Team. Members of that Advisory Team were: David Harrington (Cabletron Systems Inc.) Jeff Johnson (Cisco Systems) David Levi (SNMP Research Inc.) John Linn (Openvision) Russ Mundy (Trusted Information Systems) chair Shawn Routhier (Epilogue) Glenn Waters (Nortel) Bert Wijnen (IBM T. J. Watson Research Center) As recommended by the Advisory Team and the SNMPv3 Working Group Charter, the design incorporates as much as practical from previous RFCs and drafts. As a result, special thanks are due to the authors of previous designs known as SNMPv2u and SNMPv2*: Jeff Case (SNMP Research, Inc.) David Harrington (Cabletron Systems Inc.) David Levi (SNMP Research, Inc.) Keith McCloghrie (Cisco Systems) Harrington/Wijnen Expires February 1998 [Page 53] Draft An Architecture for SNMP Management Frameworks August 1997 Brian O'Keefe (Hewlett Packard) Marshall T. Rose (Dover Beach Consulting) Jon Saperia (BGS Systems Inc.) Steve Waldbusser (International Network Services) Glenn W. Waters (Bell-Northern Research Ltd.) Harrington/Wijnen Expires February 1998 [Page 54] Draft An Architecture for SNMP Management Frameworks August 1997 9. References [RFC1155] Rose, M., and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based internets", STD 16, RFC 1155, May 1990. [RFC1157] Case, J., M. Fedor, M. Schoffstall, and J. Davin, "The Simple Network Management Protocol", STD 15, RFC 1157, University of Tennessee at Knoxville, Performance Systems s International, Performance International, and the MIT Laboratory for Computer Science, May 1990. [RFC1212] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD 16, RFC 1212, March 1991. [RFC1901] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S., Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996. [RFC1902] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S., Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1902, January 1996. [RFC1903] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1903, January 1996. [RFC1904] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S., Waldbusser, "Conformance Statements for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1904, January 1996. [RFC1905] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S., Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, January 1996. [RFC1906] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1906, January 1996. [RFC1907] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Management Information Base for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1907 January 1996. [RFC1908] The SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Coexistence between Version 1 and Version 2 of the SNMP-standard Network Management Harrington/Wijnen Expires February 1998 [Page 55] Draft An Architecture for SNMP Management Frameworks August 1997 Framework", RFC 1908, January 1996. [RFC1909] McCloghrie, K., Editor, "An Administrative Infrastructure for SNMPv2", RFC1909, February 1996 [RFC1910] Waters, G., Editor, "User-based Security Model for SNMPv2", RFC1910, February 1996 [SNMP-MPD] The SNMPv3 Working Group, Case, J., Harrington, D., Wijnen, B., "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", draft-ietf-snmpv3-mpc-03.txt, August 1997 [SNMP-USM] The SNMPv3 Working Group, Blumenthal, U., Wijnen, B., "The User-Based Security Model for Version 3 of the Simple Network Management Protocol (SNMPv3)", draft-ietf-snmpv3-usm-01.txt, August 1997. [SNMP-ACM] The SNMPv3 Working Group, Wijnen, B., Presuhn, R., McCloghrie, K., "View-based Access Control Model for the Simple Network Management Protocol (SNMP)", draft-ietf-snmpv3-acm-02.txt, August 1997. [SNMP-APPL] The SNMPv3 Working Group, Levi, D. B., Meyer, P., Stewart, B., "SNMPv3 Applications", <draft-ietf-snmpv3-appl-01.txt>, August 1997 Harrington/Wijnen Expires February 1998 [Page 56] Draft An Architecture for SNMP Management Frameworks August 1997 APPENDIX A A. Guidelines for Model Designers This appendix describes guidelines for designers of models which are expected to fit into the architecture defined in this document. SNMPv1 and SNMPv2c are two SNMP frameworks which use communities to provide trivial authentication and access control. SNMPv1 and SNMPv2c Frameworks can coexist with Frameworks designed according to this architecture, and modified versions of SNMPv1 and SNMPv2c Frameworks could be designed to meet the requirements of this architecture, but this document does not provide guidelines for that coexistence. Within any subsystem model, there should be no reference to any specific model of another subsystem, or to data defined by a specific model of another subsystem. Transfer of data between the subsystems is deliberately described as a fixed set of abstract data elements and primitive functions which can be overloaded to satisfy the needs of multiple model definitions. Documents which define models to be used within this architecture SHOULD use the standard primitives between subsystems, possibly defining specific mechanisms for converting the abstract data elements into model-usable formats. This constraint exists to allow subsystem and model documents to be written recognizing common borders of the subsystem and model. Vendors are not constrained to recognize these borders in their implementations. The architecture defines certain standard services to be provided between subsystems, and the architecture defines abstract service interfaces to request these services. Each model definition for a subsystem SHOULD support the standard service interfaces, but whether, or how, or how well, it performs the service is dependent on the model definition. A.1. Security Model Design Requirements A.1.1. Threats A document describing a Security Model MUST describe how the model protects against the threats described under "Security Requirements of this Architecture", section 1.4. A.1.2. Security Processing Received messages MUST be validated by a Model of the Security Subsystem. Validation includes authentication and privacy processing Harrington/Wijnen Expires February 1998 [Page 57] Draft An Architecture for SNMP Management Frameworks August 1997 if needed, but it is explicitly allowed to send messages which do not require authentication or privacy. A received message contains a specified Level of Security to be used during processing. All messages requiring privacy MUST also require authentication. A Security Model specifies rules by which authentication and privacy are to be done. A model may define mechanisms to provide additional security features, but the model definition is constrained to using (possibly a subset of) the abstract data elements defined in this document for transferring data between subsystems. Each Security Model may allow multiple security protocols to be used concurrently within an implementation of the model. Each Security Model defines how to determine which protocol to use, given the securityLevel and the security parameters relevant to the message. Each Security Model, with its associated protocol(s) defines how the sending/receiving entities are identified, and how secrets are configured. Authentication and Privacy protocols supported by Security Models are uniquely identified using Object Identifiers. IETF standard protocols for authentication or privacy should have an identifier defined within the snmpAuthProtocols or the snmpPrivProtocols subtrees. Enterprise specific protocol identifiers should be defined within the enterprise subtree. For privacy, the Security Model defines what portion of the message is encrypted. The persistent data used for security should be SNMP-manageable, but the Security Model defines whether an instantiation of the MIB is a conformance requirement. Security Models are replaceable within the Security Subsystem. Multiple Security Model implementations may exist concurrently within an SNMP engine. The number of Security Models defined by the SNMP community should remain small to promote interoperability. A.1.3. Validate the security-stamp in a received message A Message Processing Model requests that a Security Model: - verifies that the message has not been altered, - authenticates the identification of the principal for whom the message was generated. - decrypts the message if it was encrypted. Additional requirements may be defined by the model, and additional services may be provided by the model, but the model is constrained to use the following primitives for transferring data between Harrington/Wijnen Expires February 1998 [Page 58] Draft An Architecture for SNMP Management Frameworks August 1997 subsystems. Implementations are not so constrained. A Message Processing Model uses the processMsg primitive as described in section 4.5. A.1.4. Security MIBs Each Security Model defines the MIB module(s) required for security processing, including any MIB module(s) required for the security protocol(s) supported. The MIB module(s) SHOULD be defined concurrently with the procedures which use the MIB module(s). The MIB module(s) are subject to normal access control rules. The mapping between the model dependent security ID and the securityName MUST be able to be determined using SNMP, if the model dependent MIB is instantiated and if access control policy allows access. A.1.5. Cached Security Data For each message received, the Security Model caches the state information such that a Response message can be generated using the same security information, even if the Local Configuration Datastore is altered between the time of the incoming request and the outgoing response. A Message Processing Model has the responsibility for explicitly releasing the cached data if such data is no longer needed. To enable this, an abstract securityStateReference data element is passed from the Security Model to the Message Processing Model. The cached security data may be implicitly released via the generation of a response, or explicitly released by using the stateRelease primitive, as described in section 4.1. Harrington/Wijnen Expires February 1998 [Page 59] Draft An Architecture for SNMP Management Frameworks August 1997 A.2. Message Processing Model Design Requirements An SNMP engine contains a Message Processing Subsystem which may contain multiple Message Processing Models. The Message Processing Model MUST always (conceptually) pass the complete PDU, i.e. it never forwards less than the complete list of varBinds. A.2.1. Receiving an SNMP Message from the Network Upon receipt of a message from the network, the Dispatcher in the SNMP engine determines the version of the SNMP message and interacts with the corresponding Message Processing Model to determine the abstract data elements. A Message Processing Model specifies the SNMP Message format it supports and describes how to determine the values of the abstract data elements (like msgID, msgMaxSize, msgFlags, msgSecurityParameters, securityModel, securityLevel etc). A Message Processing Model interacts with a Security Model to provide security processing for the message using the processMsg primitive, as described in section 4.5. A.2.2. Sending an SNMP Message to the Network The Dispatcher in the SNMP engine interacts with a Message Processing Model to prepare an outgoing message. For that it uses the following primitives: - for requests and notifications: prepareOutgoingMessage, as described in section 4.4 - for response messages: prepareResponseMessage, as described in section 4.4 A Message Processing Model, when preparing an Outgoing SNMP Message, interacts with a Security Model to secure the message. For that it uses the following primitives: - for requests and notifications: generateRequestMsg, as described in section 4.5. - for response messages: generateResponseMsg as described in section 4.5. Once the SNMP message is prepared by a Message Processing Model, the Dispatcher sends the message to the desired address using the appropriate transport. A.3. Application Design Requirements Harrington/Wijnen Expires February 1998 [Page 60] Draft An Architecture for SNMP Management Frameworks August 1997 Within an application, there may be an explicit binding to a specific SNMP message version, i.e. a specific Message Processing Model, and to a specific Access Control Model, but there should be no reference to any data defined by a specific Message Processing Model or Access Control Model. Within an application, there should be no reference to any specific Security Model, or any data defined by a specific Security Model. An application determines whether explicit or implicit access control should be applied to the operation, and, if access control is needed, which Access Control Model should be used. An application has the responsibility to define any MIB module(s) used to provide application-specific services. Applications interact with the SNMP engine to initiate messages, receive responses, receive asynchronous messages, and send responses. A.3.1. Applications that Initiate Messages Applications may request that the SNMP engine send messages containing SNMP commands or notifications using the sendPdu primitive as described in section 4.2. If it is desired that a message be sent to multiple targets, it is the responsibility of the application to provide the iteration. The SNMP engine assumes necessary access control has been applied to the PDU, and provides no access control services. The SNMP engine looks at the "expectResponse" parameter, and if a response is expected, then the appropriate information is cached such that a later response can be associated to this message, and can then be returned to the application. A sendPduHandle is returned to the application so it can later correspond the response with this message as well. A.3.2. Applications that Receive Responses The SNMP engine matches the incoming response messages to outstanding messages sent by this SNMP engine, and forwards the response to the associated application using the processResponsePdu primitive, as described in section 4.2. A.3.3. Applications that Receive Asynchronous Messages When an SNMP engine receives a message that is not the response to a request from this SNMP engine, it must determine to which application the message should be given. Harrington/Wijnen Expires February 1998 [Page 61] Draft An Architecture for SNMP Management Frameworks August 1997 An Application that wishes to receive asynchronous messages registers itself with the engine using the primitive registerContextEngineID as described in section 4.2. An Application that wishes to stop receiving asynchronous messages should unregister itself with the SNMP engine using the primitive unregisterContextEngineID as described in section 4.2. Only one registration per combination of PDU type and contextEngineID is permitted at the same time. Duplicate registrations are ignored. An errorIndication will be returned to the application that attempts to duplicate a registration. All asynchronously received messages containing a registered combination of PDU type and contextEngineID are sent to the application which registered to support that combination. The engine forwards the PDU to the registered application, using the processPdu primitive, as described in section 4.2. A.3.4. Applications that Send Responses Request operations require responses. An application sends a response via the returnResponsePdu primitive, as described in section 4.2. The contextEngineID, contextName, securityModel, securityName, securityLevel, and stateReference parameters are from the initial processPdu primitive. The PDU and statusInformation are the results of processing. A.4. Access Control Model Design Requirements An Access Control Model determines whether the specified securityName is allowed to perform the requested operation on a specified managed object. The Access Control Model specifies the rules by which access control is determined. The persistent data used for access control should be manageable using SNMP, but the Access Control Model defines whether an instantiation of the MIB is a conformance requirement. The Access Control Model must provide the primitive isAccessAllowed Harrington/Wijnen Expires February 1998 [Page 62] Draft An Architecture for SNMP Management Frameworks August 1997 Table of Contents 0. Issues 2 0.1. Resolved Issues 2 0.1.1. Issues discussed at second Interim Meeting: 3 0.2. Change Log 4 1. Introduction 10 1.1. Overview 10 1.2. SNMP Management Systems 10 1.3. Goals of this Architecture 11 1.4. Security Requirements of this Architecture 12 1.5. Design Decisions 13 2. Documentation Overview 15 2.1. Document Roadmap 16 2.2. Applicability Statement 16 2.3. Coexistence and Transition 16 2.4. Transport Mappings 17 2.5. Message Processing 17 2.6. Security 17 2.7. Access Control 17 2.8. Protocol Operations 18 2.9. Applications 18 2.10. Structure of Management Information 18 2.11. Textual Conventions 18 2.12. Conformance Statements 18 2.13. Management Information Base Modules 19 2.13.1. SNMP Instrumentation MIBs 19 2.14. SNMP Framework Documents 19 2.15. Operational Overview 21 3. Elements of the Architecture 23 3.1. The Naming of Entities 23 3.1.1. SNMP entity 24 3.1.2. SNMP engine 24 3.1.3. snmpEngineID 24 3.1.4. Dispatcher 24 3.1.5. Message Processing Subsystem 25 3.1.6. Message Processing Model 25 3.1.7. Security Subsystem 26 3.1.8. Security Model 26 3.1.9. Security Protocol 26 3.1.10. Access Control Subsystem 27 3.1.11. Access Control Model 27 3.1.12. Applications 28 3.1.13. SNMP Agent 28 3.1.14. SNMP Manager 28 3.2. The Naming of Identities 29 3.2.1. Principal 29 3.2.2. securityName 29 3.2.3. Model dependent security ID 29 3.3. The Naming of Management Information 30 3.3.1. An SNMP Context 31 3.3.2. contextEngineID 31 3.3.3. contextName 31 Harrington/Wijnen Expires February 1998 [Page 63] Draft An Architecture for SNMP Management Frameworks August 1997 3.3.4. scopedPDU 32 3.4. Other Constructs 32 3.4.1. maxSizeResponseScopedPDU 32 3.4.2. Local Configuration Datastore 32 3.4.3. securityLevel 32 4. Abstract Service Interfaces. 33 4.1. Common Primitives 33 4.1.1. Release State Reference Information 33 4.2. Dispatcher Primitives 33 4.2.1. Generate Outgoing Request or Notification 33 4.2.2. Process Incoming Request or Notification PDU 34 4.2.3. Generate Outgoing Response 34 4.2.4. Process Incoming Response PDU 34 4.2.5. Registering Responsibility for Handling SNMP PDUs. 35 4.3. Message Processing Subsystem Primitives 35 4.3.1. Prepare an Outgoing SNMP Request or Notification Message 35 4.3.2. Prepare an Outgoing SNMP Response Message 36 4.3.3. Prepare Data Elements from an Incoming SNMP Message 36 4.4. Access Control Subsystem Primitives 37 4.5. Security Subsystem Primitives 37 4.5.1. Generate a Request or Notification Message 37 4.5.2. Process Incoming Message 37 4.5.3. Generate a Response Message 38 4.6. User Based Security Model Internal Primitives 38 4.6.1. User-based Security Model Primitives for Authentication 38 4.6.2. User-based Security Model Primitives for Privacy 39 4.7. Scenario Diagrams 40 4.7.1. Command Generator or Notification Originator Application 40 4.7.2. Scenario Diagram for a Command Responder Application 41 5. Definition of Managed Objects for SNMP Management Frameworks 42 6. Security Considerations 51 7. Editor's Addresses 52 8. Acknowledgements 53 9. References 55 A. Guidelines for Model Designers 57 A.1. Security Model Design Requirements 57 A.1.1. Threats 57 A.1.2. Security Processing 57 A.1.3. Validate the security-stamp in a received message 58 A.1.4. Security MIBs 59 A.1.5. Cached Security Data 59 A.2. Message Processing Model Design Requirements 60 A.2.1. Receiving an SNMP Message from the Network 60 A.2.2. Sending an SNMP Message to the Network 60 A.3. Application Design Requirements 60 A.3.1. Applications that Initiate Messages 61 A.3.2. Applications that Receive Responses 61 A.3.3. Applications that Receive Asynchronous Messages 61 A.3.4. Applications that Send Responses 62 A.4. Access Control Model Design Requirements 62 Harrington/Wijnen Expires February 1998 [Page 64]