Architecture for the Next Generation Simple Network Management Protocol (SNMPng) 9 May 1997 D. Harrington Cabletron Systems, Inc. dbh@cabletron.com B. Wijnen IBM T.J. Watson Research wijnen@vnet.ibm.com 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 the Next-Generation of the Simple Network Management Protocol (SNMPng). The architecture is designed to be modular to allow the evolution of the protocol over time. The major portions of the architecture are 1) a message processing and control subsystem, 2) a security subsystem, and 3) a local processing subsystem. Harrington/Wijnen Expires November 1977 [Page 1] \ Draft Architecture for SNMPng May 1997 0. Change Log [version 2.2] . fix PDU back to scopedPDU where appropriate . MIB definitions contained some terms that need defining (MMS, etc) look them up and add to "abstract data elements" . fixes suggested by Bob Moore: contextID identifies engine not agent . fixed intro to allow manager-to-manager "conveyance" . For interfaces which pass both the securityCookie and the security model, removed the securityModel, since it can be derived from the securityCookie. . eliminated requirement of group to mapping, since movement of traps to application eliminates the need for this mapping. . eliminated "end-user"; substitutes security entity. . removed discussion of traps as part of LPM, replaced with discussion of notifications sent/received by application. . separated architectural textual conventions from MPC-specific MIB (put TCs in architecture doc, objects in MPC doc) . changed security entity to securityIdentity [version 2.1] . changed Quality of Service (QoS) to Level of Security (LoS) . changed QoS field to msgFlags (includes LoS plus reportFlag) . modified "Abstract Functionality" . expanded subsystem descriptions to include introductory text on SMI, textual conventions, conformance, protocol operations, SNMP MIB, coexistence, etc. . added reference citations as needed . replaced "interface" with "abstract data elements to transfer data" to avoid the dreaded "interface = API" assumption. . modified scopedPDU text to permit a snmpv1 community-scoped PDU, including one which uses the community to control proxy i.e snmpv3 uses engineID/contextName for naming scope snmpv1 uses community alone for naming scope a snmpv1 MPC can "scope" the snmpv1 PDU by using the community as the the naming scope in the interface between MPC and LPM or Apps . rewrote (and renamed) "Abstract Data Elements of the Architecture" . added a definition for an abstract "engineID . modified naming scope and scopedPDU to be more generic . removed the MIB definitions [version 2.0] . separated architecture from Message Processing and Control model for SNMPv3 . changed filename to internet-drafts assigned name . changed contextID to contextEngineID . changed sub-frameworks to subsystems . changed Model to model . changed scopedPDU to PDU . expanded acronyms . removed reference citations to arch, mpc, and usec drafts Harrington/Wijnen Expires November 1977 [Page 2] \ Draft Architecture for SNMPng May 1997 Harrington/Wijnen Expires November 1977 [Page 3] \ Draft Architecture for SNMPng May 1997 1. Introduction A management system contains: several (potentially many) nodes, each with a processing entity, termed an agent, which has access to management instrumentation; at least one management station; and, a management protocol, used to convey management information between the agents and management stations, or between management stations and other management stations. Management stations execute management applications which 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. Operations of the protocol are carried out under an administrative framework which defines minimum policies for mechanisms which provide message-level security, access control for managed objects, and interaction between the protocol engine and the applications which use the services of the engine. 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 implementors of both minimal agents and full-function network enterprise management stations. 1.1. A Note on Terminology 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 an updated design of portions of SNMPv1, as described in RFCs 1902-1908. SNMP next generation (SNMPng) is an architecture designed to allow an orderly evolution of SNMP subsystems. This document describes the SNMPng architecture. Throughout the rest of this document, the term subsystem will refer to an abstract and incomplete specification of a portion of SNMPng, that will be 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 a design to make it possible to implement the specification. A Implementation is an instantiation of a subsystem, conforming to a specific model. Harrington/Wijnen Expires November 1977 [Page 4] \ Draft Architecture for SNMPng May 1997 2. Overview The architecture presented here emphasizes the use of modularity to allow the evolution of portions of SNMP without requiring a redesign of the general architecture of SNMP. The processing of SNMP messages is procedural - there are specific steps which must be accomplished in specific order of processing. These steps fall into general categories of similar functionality. This document will describe major abstractions of functionality required of an SNMP engine, and the abstract interactions between these major categories of functionality. This document will describe how this architecture is meant to allow modules of functionality corresponding to these abstract categories to be designed to allow the evolution of the whole by modifying discrete modules within the architecture. Harrington/Wijnen Expires November 1977 [Page 5] \ Draft Architecture for SNMPng May 1997 3. An Evolutionary Architecture - Design Goals The goals of the architectural design are to use encapsulation, cohesion, hierarchical rules, and loose coupling to reduce complexity of design and make the evolution of portions of the architecture possible. 3.1. Encapsulation Encapsulation describes the practice of hiding the details that are used internal to a process. Some data is required for a given procedure, but isn't needed by any other part of the process. In networking, the concept of a layered stack reflects this approach. The transport layer contains data specific to its processing; the data is not visible to the other layers. In programming this is reflected in language elements such as "file static" variables in C, and "private" in C++, etc. In the SNMPng architecture, all data used for processing only within a functional portion of the architecture should have its visibility restricted to that portion if possible. The data should be accessed only by that functionality defined with the data. No reference to the data should be made from outside the functional portion of the architecture, except through predefined public interfaces. 3.2. Cohesion Similar functions can be grouped together and their differences ignored, so they can be dealt with as a single entity. It is important that the functions which are grouped together are actually similar. For instance, authentication and encryption are both security functions which act on the message. Access control, while similar in some ways, is not similar in that it does not work on the message, it works on the contents of the message. The similarity of the data used to perform functions can be a good indicator of the similarity of the functions. Similar functions, especially those that use the same data elements, should be defined together. The security functions which operate at the message level should be defined in a document together with the definitions for those data elements that are used only by those security functions. For example, a MIB with authentication keys is used only by authentication functions; they should be defined together. 3.3. Hierarchical Rules Functionality can be grouped into hierarchies where each element in the hierarchy receives general characteristics from its direct superior, and passes on those characteristics to each of its direct subordinates. The SNMPng architecture uses the hierarchical approach by defining Harrington/Wijnen Expires November 1977 [Page 6] \ Draft Architecture for SNMPng May 1997 subsystems, which specify the general rules of a portion of the system, models which define the specific rules to be followed by an implementation of the portion of the system, and implementations which encode those rules into reality for a portion of the system. It is expected that within portions of the system, hierarchical relationships will be used to compartmentalize, or modularize, the implementation of specific functionality. For example, it is expected that within the security portion of the system, authentication and privacy will probably be contained in separate modules, and that multiple authentication and privacy mechanisms will be supported by allowing supplemental modules that provide protocol-specific authentication and privacy services. 3.4. Coupling Coupling describes the amount of interdependence between parts of a system. Loose coupling indicates that two sub-systems are relatively independent of each other; tight coupling indicates a high degree of mutual dependence. To make it possible to evolve the architecture by replacing only part of the system, or by supplementing existing portions with alternate mechanisms for similar functionality, without obsoleting the complete system, it is necessary to limit the coupling of the parts. Encapsulation and cohesion help to reduce coupling by limiting the visibility of those parts that are only needed within portions of a system. Another mechanism is to constrain the nature of interactions between various parts of the system. This can be done by defining fixed, generic, flexible interfaces for transferring data between the parts of the system. The concept of plug-and-play hardware components is based on that type of interface between the hardware component and system into which it will be "plugged." SNMPng has chosen this approach so individual portions of the system can be upgraded over time, while keeping the overall system intact. To avoid specifying fixed interfaces, which would constrain a vendor's choice of implementation strategies, SNMPng defines a set of abstract data elements to be used for (conceptually) transferring data between subsystems in documents which describe subsystem or model interactions. Documents describing the interaction of subsystems or models should use only the abstract data elements provided for transferring data but vendors are not constrained to using the described data elements for transferring data between portions of their implementation. Loose coupling works well with the IETF standards process. If we separate message-handling from security and from local processing, Harrington/Wijnen Expires November 1977 [Page 7] \ Draft Architecture for SNMPng May 1997 then the separate portions of the system can move through the standards process with less dependence on the status of the other portions of the standard. Security models may be able to be re-opened for discussion due to patents, new research, export laws, etc., as is clearly expected by the WG, without needing to reopen the documents which detail the message format or the local processing of PDUs. Thus, the standards track status of related, but independent, documents is not affected. Harrington/Wijnen Expires November 1977 [Page 8] \ Draft Architecture for SNMPng May 1997 4. Abstract Functionality The architecture described here is composed of four subsystems, each capable of being defined as different models which may be replaced or supplemented as the growing needs of network management require. The subsystems are a Message Processing and Control subsystem, a Security subsystem, a Local Processing subsystem, and an Application Support subsystem. The term "engine" refers to a combination of Message Processing and Control subsystem(s), Security subsystem(s), and Local Processing subsystem(s). Applications are external processes which use the engine to send or receive SNMP messages, or otherwise use the services of the SNMP engine, to accomplish their tasks. 4.1. Message Processing and Control The Message Processing and Control subsystem of an SNMP engine interacts with the network using SNMP messages, and interacts with applications using data elements defined by the Message Processing and Control model, within the constraints of the Architecture. A Message Processing and Control model has the responsibility for coordinating the sending and receiving of SNMP messages, and for coordinating the interaction with other subsystems to acquire the desired services for the processing of a message. 4.1.1. Transport Mappings SNMP messages are sent to, or received from, the network using a transport mechanism. It is the purpose of Transport Mapping documents to define how SNMP maps onto transport domains. A Message Processing and Control model defines which Transport Mappings documents are supported by the model. 4.1.2. SNMP-Based Message Formats SNMP messages sent to, or received from, the network use a format defined by the Message Processing and Control model. 4.1.3. Application-Based Message Formats Messages being sent to, or received from, applications use formats which are defined by the Message Processing and Control Model. Note that these are not SNMP messages, but are abstract data elements used to transfer data between the Message Processing and Control subsystem and an Application Support subsystem. 4.1.4. Protocol Instrumentation Harrington/Wijnen Expires November 1977 [Page 9] \ Draft Architecture for SNMPng May 1997 It is the purpose of a Management Information Base for SNMP document to define managed objects which describe the behavior of an SNMP engine. A Message Processing and Control model defines which SNMP MIB Module documents are supported to instrument the model. 4.2. 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. 4.3. Local Processing Local Processing deals with the contents of messages, called the PDU, providing access to instrumentation and applying access control according the rules of the Local Processing model being used. An overview of management information and processing operations is provided here, but a Local Processing model defines which set of documents are used to specifically define the structure of management information, textual conventions, conformance requirements, and operations supported by the model. During local processing, it may be required to control access to certain instrumentation for certain operations. The enforcement of access rights requires the means to identify the access allowed for the securityIdentity on whose behalf a request is generated. A Local Processing model defines which set of documents are used to define the mechanisms to realize access control within that model. 4.3.1. 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. A Local Processing model defines which SMI documents are supported by the model. Harrington/Wijnen Expires November 1977 [Page 10] \ Draft Architecture for SNMPng May 1997 4.3.2. 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. A Local Processing model defines which Textual Conventions documents are supported by the model. 4.3.3. Conformance Statements 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. A Local Processing model defines which Conformance Statement documents are supported by the model. 4.3.4. Protocol Operations SNMP messages encapsulate a 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. A Local Processing model defines which Protocol Operations documents are supported by the model. 4.4. Applications Applications are developed to achieve certain goals. They use the SNMP engine to achieve their goals, and interact with the engine in a manner consistent with the SNMP architecture, but the purpose of specific applications is outside the scope of the SNMP architecture. Applications interact with the SNMP engine using application-support messages whose format is defined by the Message Processing and Control model in use. 4.5 Coexistence 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 a Coexistence document is to detail recognized anomalies and to describe required and recommended behaviors for resolving the interactions between models within the architecture. Harrington/Wijnen Expires November 1977 [Page 11] \ Draft Architecture for SNMPng May 1997 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. Harrington/Wijnen Expires November 1977 [Page 12] \ Draft Architecture for SNMPng May 1997 5. Abstract Data Elements of the Architecture This section contains definitions of abstract data elements used to transfer data between subsystems. 5.1 engineID Each SNMP engine, consisting of potentially many subsystems, must be able to be uniquely identified. The mechanism by which this can be done is defined the Message Processing and Control model in use. DBH: this is so the IP or MAC address can be used as the engineID for old snmpv1 implementations which are being retrofitted into this architecture for use with old snmpv1 management stations. A partial alternative would be to define the engineID MIB as a separate module that can be recognized and supported by snmpv1 engines as well as newer engines that fit this architecture. 5.2. SecurityIdentity A generic term for an uniquely-identifiable entity on whose behalf a message can be generated. The term is deliberately abstract to allow the security subsystem to define the format and nature of the identities it will use. Sample securityIdentities include communities [RFC1157], parties [RFC1445], and users [RFC1910]. 5.3. Level of Security Messages may require different levels of security. The acronym LoS is used to refer to the level of security. SNMPng recognizes three levels of security: - without authentication and without privacy (noAuth/noPriv) - with authentication but without privacy (auth/noPriv) - with authentication and with privacy (auth/Priv) Every message has an associated LoS; all subsystems (security, access control, applications, message processing and control) are required to abide the specified LoS. 5.4. Groups A Group identifies a set of zero or more security entities on whose behalf SNMP managed objects are being processed, subject to access control policies common to all members of the group. 5.5. Contexts An SNMP context is a collection of management information Harrington/Wijnen Expires November 1977 [Page 13] \ Draft Architecture for SNMPng May 1997 accessible by an SNMP engine. An item of management information may exist in more than one context. An SNMP engine potentially has access to many contexts. 5.6. ContextEngineID A contextEngineID is a field in a message to uniquely identify the engine that contains the context which realizes the managed objects referenced in the PDUs. 5.7. ContextName An octet string used to name a context. Each context must be uniquely named within an engine. 5.8. Naming Scope The data necessary to uniquely identify a context within an administrative domain is called a naming scope. The format of the naming scope data is defined by a Message Processing and Control model. 5.9. Scoped-PDU A scopedPDU contains a Naming-Scope and a PDU. The Naming Scope unambiguously identifies, within the administrative domain, the context to which the SNMP management information in the PDU refers. The PDU format is defined by the Local Processing model in use, or by a document referenced by the Local processing model. 5.10. PDU-MMS the maximum size of a scopedPDU to be included in a response message, given the amount of reserved space in the message for the anticipated security parameters. 5.11. Security Configuration Datastore Each Security model may need to retain its own set of information about security entities, mechanisms, and policies. The collection of these, possibly multiple, sets of information is referred to collectively as the SNMPng engine's Security Configuration Datastore (SCD). In order to allow an SNMPng engine's SCD to be remotely configured, portions may need to be accessible as managed objects. 5.12. Local Configuration Datastore Harrington/Wijnen Expires November 1977 [Page 14] \ Draft Architecture for SNMPng May 1997 Each Local Processing model may need to retain its own set of information about access control, naming scopes, and policies. The collection of these, possibly multiple, sets of information is referred to collectively was the SNMPng engine's Local Processing Configuration Datastore (LCD). In order to allow an SNMPng engine's LCD to be remotely configured, portions may need to be accessible as managed objects. Harrington/Wijnen Expires November 1977 [Page 15] \ Draft Architecture for SNMPng May 1997 6. Textual Conventions for the SNMPng Architecture snmpNg-TC DEFINITIONS ::= BEGIN IMPORTS ObjectSyntax, TimeTicks FROM SNMPv2-SMI; TEXTUAL-CONVENTION FROM SNMPv2-TC; snmpNg-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, snmpModules FROM SNMPv2-SMI TEXTUAL-CONVENTION, TestAndIncr, RowStatus, AutonomousType, StorageType, TDomain, TAddress FROM SNMPv2-TC MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; snmpNgMIB MODULE-IDENTITY LAST-UPDATED "9703260000Z" -- 26 Mar 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 email: mundy@tis.com phone: 301-854-6889 Co-editor: Dr. Jeffrey Case Snmp Research International, Inc. postal: phone: Co-editor Dave Harrington Cabletron Systems, Inc postal: Post Office Box 5005 MailStop: Durham 35 Industrial Way Rochester NH 03867-5005 email: dbh@cabletron.com phone: 603-337-7357 " DESCRIPTION "The snmpNg architecture MIB" ::= { snmpModules xx } Harrington/Wijnen Expires November 1977 [Page 16] \ Draft Architecture for SNMPng May 1997 -- Textual Conventions used throughout the SNMPng Framework SnmpNgEngineID ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An SNMPng engine's administratively-unique identifier. The value for this object may not be all zeros or all 'ff'H. The initial value for this object may be configured via an operator console entry or via an algorithmic function. In the later case, the following guidelines are recommended: 1) 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. 2) The remaining eight octets are the cookie whose contents 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, the cookie may be the IP address of the agent, 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 cookie be further divided into one octet that indicates the method being used and seven octets which are a function of the method. " SYNTAX OCTET STRING (SIZE (12)) SnmpNgMms OBJECT-TYPE SYNTAX INTEGER(0..65535) MAX-ACCESS read-only STATUS current DESCRIPTION "The maximum length in octets of an SNMP message which this SNMPng engine will accept using any transport mapping. " ::= { snmpV3MPCMIBObjects 2 } SnmpNgSecurityModel ::= TEXTUAL-CONVENTION Harrington/Wijnen Expires November 1977 [Page 17] \ Draft Architecture for SNMPng May 1997 STATUS current DESCRIPTION "An identifier that uniquely identifies a model of security subsystem within the SNMPng Framework. " SYNTAX INTEGER(0..2147483647) SnmpNgSecurityIdentity ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A octet string which contains data in a format defined by a security model which identifies a unique for which messages may be generated. For example, a securityIdentity for user-based security contains a user; a securityIdentity for community-based security contains a community. The format is not restricted to human-readable text. " SYNTAX OCTET STRING (SIZE (0..32)) SnmpNgLoS ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A level of security at which SNMP messages can be sent; in particular, one of: noAuth - without authentication and without privacy, auth - with authentication but without privacy, priv - with authentication and with privacy. " SYNTAX INTEGER { noAuth(1), auth(2), priv(3) } SnmpNgGroupName ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An octet string which identifies a set of zero or more security entities on whose behalf SNMP managed objects are being processed, subject to access control policies common to all members of the group. " SYNTAX OCTET STRING (SIZE(1..16)) SnmpNgContextName ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A name which uniquely identifies a set of management information realized by an SNMP engine. " SYNTAX OCTET STRING (SIZE (0..32)) END Harrington/Wijnen Expires November 1977 [Page 18] \ Draft Architecture for SNMPng May 1997 7. Model Design Requirements The basic design elements come from SNMPv2u and SNMPv2*, as described in RFCs 1909-1910, and from a set of internet drafts. these are the two most popular de facto "administrative framework" standards that include security and access control for SNMPv2. SNMPv1 and SNMPv2c [RFC1901] are two administrative frameworks based on communities to provide trivial authentication and access control. SNMPng allows implementations to add support for features of SNMPv1 and SNMPv2c, and to coexist with SNMPv1 and SNMPv2c engines, 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. For any subsystem model, the model definition is constrained to using the abstract data elements, defined in this document, for transferring data between the subsystem and any other subsystem. (Note that the model definition is so constrained, but implementations are not so constrained). 7.1. Security Model Design Requirements Received messages must be validated by a model of the Security subsystem. Validation includes authentication and privacy processing if needed, but it is explicitly allowed to send messages which do not require authentication or privacy. A received message will contain 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 mechanisms to be used concurrently within an implementation of the model. Each Security model defines how to determine which protocol to use, given the LoS and the security parameters relevant to the message. Each Security model, with its associated protocol(s) defines how the sending/receiving entities are identified, how secrets are configured, and how security entities map to groups. For privacy, the Security model defines what portion of the message is encrypted. Harrington/Wijnen Expires November 1977 [Page 19] \ Draft Architecture for SNMPng May 1997 Security models are replaceable within the SNMPng subsystem. Multiple Security model Implementations may exist concurrently within an engine. The number of Security models defined by the SNMP community should remain small to promote interoperability. It is required that an implementation of the User-Based Security model be used in all engines to ensure at least a minimal level of interoperability. Each Security model must define a mapping to be used between a unique securityIdentity within the model's SCD, and a securityCookie. A securityCookie is an implementation-specific handle to identify the securityIdentity to which it maps. If an implementation supports multiple Security models, the securityCookie must include a mechanism for determining which Security model SCD is referenced. The securityCookie, in combination with the engineID of the engine which instantiates the securityCookie, can be used as a globally-unique identifier for a securityIdentity. The type of a securityCookie is an OCTET STRING, but the format of the contents is implementation-specific. It is important to note that since the securityCookie may be accessible outside the engine, the securityCookie must not disclose any sensitive data, such as by including passwords in open text in the securityCookie. Each Security model defines the MIB moduless required for security processing, including any MIB modules required for the security mechanism(s) supported. The MIB modules must be defined concurrently with the procedures which use the MIB module. The MIB modules are subject to normal security and access control rules. 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. The mapping between a securityCookie and the unique securityIdentity within the engine must be able to be determined using SNMP, if the MIB is instantiated and access control policy allows. Protocols should be uniquely identified using Object Identifiers. Enterprise-specific protocols should be defined within the enterprise subtree. A protocolID MIB should be defined for IETF standard protocols for authentication and privacy. 7.2. Local Processing Model Design Requirements Within any Local Processing model, there should be no reference to any specific Security model, or any specific Message Processing and Control model, or any data defined by a specific Security or Message Processing and Control model. A Local Processing model only processes PDUs which are destined for processing by the current engine, according to the rules of the Local Processing model. Harrington/Wijnen Expires November 1977 [Page 20] \ Draft Architecture for SNMPng May 1997 A Local Processing model must determine whether the specified group is allowed to perform the requested operation on the managed objects in the PDU, according to the rules of the Local Processing model being used. A Local Processing model specifies the rules by which access control and PDU processing are to be done. A model may define mechanisms to provide additional processing features, but is constrained to using the abstract data elements defined in this document for transferring data between subsystems. The persistent data used for local processing should be manageable using SNMP, but the Local Processing model defines whether an instantiation of the MIB is a conformance requirement. 7.3. Message Processing and Control Requirements Within any Message Processing and Control model, there should be no reference to any specific Security model or any specific Local Processing model, or to any data defined by a specific Security or Local Processing model. The Message Processing and Control model must always (conceptually) pass the complete PDU, i.e. it never forwards less than the complete list of varbinds. The Message Processing and Control model specifies how to determine whether the PDU in a received message should be processed by the current engine or by an application [FT]. A model may define mechanisms to provide additional processing features, but is constrained to using the abstract data elements defined in this document for transferring data between subsystems. 7.4. Applications Applications are beyond the scope of this document, but there are certain issues that must be clarified regarding the relation and the abstract data elements used for transferring data between applications and the engine. 7.4.1. Application Responsibilities An application has the responsibility to define any MIB modules used to provide application-specific services. An engine supports one conceptual interface to applications, provided using the abstract data elements for transferring data between the engine and applications. It is implementation-specific how data passed from the engine is routed to the appropriate application. Harrington/Wijnen Expires November 1977 [Page 21] \ Draft Architecture for SNMPng May 1997 No access control is applied to the PDU by the engine which passes the PDU to the application. A PDU passed to an application must be a complete PDU, i.e the engine never partially processes a PDU which is to be passed to an application. Harrington/Wijnen Expires November 1977 [Page 22] \ Draft Architecture for SNMPng May 1997 8. Subsystems and Transferring Data Between Subsystems Transfer of data between the subsystems is deliberately described as a fixed set of abstract data elements which can be overloaded to satisfy the needs of multiple model definitions. Documents which define models to be used within this architecture are constrained to using the abstract data elements for transferring data between subsystems, possibly defining specific mechanisms for converting the abstract data 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 data elements to transfer the data necessary to perform the services. Each model definition for a subsystem must support the standard service interfaces, but whether, or how, or how well, it performs the service is defined by the model definition. 8.1. Standard Services of Message Processing and Control Models 8.1.1. Receive SNMP messages from the network Upon receipt of an SNMPng message from the network, a Message Processing and Control model will, in an implementation-defined manner, establish a mechanism for coordinating all processing regarding this received message, e.g. it may assign a "handle" to the message. The Message Processing and Control model will specify how to determine the values of the MMS, the securityModel, the LoS, and the security parameters block. The Message Processing and Control will (conceptually) pass the extracted MMS, the LoS, the message, and the block of security parameters to the appropriate Security model. The Security model, after completion of its processing, will return to the Message Processing and Control model the group, the securityCookie, the PDU-MMS, and the PDU. In the event of an error in security processing, an errorCode may be returned instead. 8.1.2. Send SNMP messages to the network The Message Processing and Control model will pass a PDU, the securityCookie, and all global data to be included in the message to Harrington/Wijnen Expires November 1977 [Page 23] \ Draft Architecture for SNMPng May 1997 the Security model. The Security model will construct the message, and return the completed message to the Message Processing and Control model, which will send the message to the desired address using the appropriate transport. 8.1.3. Coordinate the Local Processing of a Received Request Message The Message Processing and Control will receive the SNMP message according to the process described in 8.1.1. The Message Processing and Control model will specify how to determine whether the request should be processed by the Local Processing model or by an application [FT]. If the request should be processed locally, the Message Processing and Control model will (conceptually) pass the PDU, the Group, the PDU-MMS, and the LoS, to the Local Processing model. It will accept a completed PDU containing the responsePDU from the Local Processing model, and generate a response message according to the process described in 8.1.2. 8.1.4. Forward Received Request Message to an Application The Message Processing and Control will receive the SNMP message according to the process described in 8.1.1. The Message Processing and Control model will specify how to determine whether the request should be processed by the Local Processing model or by an application [FT]. If the request should be processed by an application [FT], the Message Processing and Control model will assign an implementation-defined handle to the message. The Message Processing and Control model will specify how to determine, and will (conceptually) pass the SNMP version, the LoS, the securityCookie, and the assigned handle to the application [FT]. 8.1.5. Generate a Request Message for an Application The Message Processing and Control will receive a request for the generation of an SNMP request message from an application. The application has the responsibility for providing a Destination Address, the SNMP version, the LoS desired, the securityCookie to use, a scopedPDU containing the desired operation, and a handle used for matching up an incoming response to the application making the request. The Message Processing and Control checks the verb in the PDU to determine that it is a request message, and if so, skips local processing of the PDU. Harrington/Wijnen Expires November 1977 [Page 24] \ Draft Architecture for SNMPng May 1997 The Message Processing and Control will generate the message according to the process described in 8.1.2. 8.1.6. Forward Received Response Message to an Application The Message Processing and Control will receive the SNMP message according to the process described in 8.1.1. The Message Processing and Control will determine which application is awaiting a response, using the handle assigned to the transaction in step 8.1.3 The Message Processing and Control will pass to the application the LoS, the securityCookie, the PDU-MMS, and the PDU. An Application, using the securityCookie, can determine the securityIdentity on whose behalf the response should be processed. 8.1.7. Forward Received Notification Message to an Application The Message Processing and Control will receive the SNMP message according to the process described in 8.1.1. The Message Processing and Control will determine to which application traps should be forwarded. DBH: is this true? isn't this a function of an application support subsystem to de-multiplex traps to the appropriate application? Isn't this necessarily part of SNMP, since the indication of the appropriate application may need to be provided by the SNMP message (e.g. msgID) The Message Processing and Control subsystem will pass to the application the LoS, the securityCookie, the PDU-MMS, and the PDU. An Application, using the securityCookie, can determine the securityIdentity on whose behalf the notification should be processed. 8.1.8. Send a Notification The Message Processing and Control subsystem accepts from an application a request to send a notification message. The application provides the address to which the notification should be sent, the SecurityCookie to use, the LoS, and a completed scopedPDU. Notifications are not processed by a Local Processing model, and therefore are not subject to access control of their contents. 8.1.9. Send a Response Message from an Application An application, using local information can determine the securityCookie to use to generate the message. Harrington/Wijnen Expires November 1977 [Page 25] \ Draft Architecture for SNMPng May 1997 The application will pass to the Message Processing and Control subsystem the securityCookie, the LoS, and the scopedPDU. The Message Processing and Control will send the SNMP message according to the process described in 8.1.2. 8.2. Standard Services Required of Security Models 8.2.1. validate the security-stamp in a received message given a message, the MMS, LoS, and the security parameters from that message, verify the message has not been altered, and authenticate the identification of the securityIdentity for whom the message was generated. If encrypted, decrypt the message Additional requirements may be defined by the model, and additional services provided by the model, but the model is constrained to use only the defined abstract data elements for transferring data between subsystems. Implementations are no so constrained. return a securityCookie identifying the securityIdentity for whom the message was generated and return the portions of the message needed for further processing: a PDU - a PDU containing varbinds and a verb according to the rules of the Local Processing model to be used. LoS - the level of security required. The same level of security must also be used during application of access control. MMS - the maximum size of a message able to be generated by this engine for the destination agent. PDU-MMS - the maximum size of a PDU to be included in a response message, given the amount of reserved space in the message for the anticipated security parameters. GroupName - the GroupName to be applied for access control for the securityIdentity for whom the request was generated. 8.2.2. security-stamp a message Given a PDU, LoS, MMS, and a securityCookie, the Security model must determine the security parameters for the message, the contents and format of which are defined by the model. The Security model will return a message including the appropriate security parameters, encrypted if required. 8.2.3. Provide mappings between security entities and securityCookies Harrington/Wijnen Expires November 1977 [Page 26] \ Draft Architecture for SNMPng May 1997 Given model-specific parameters to identify a securityIdentity, an Security model must return a securityCookie Given a securityCookie generated by this Security model, the Security model must return model-specific data identifying the corresponding securityIdentity. 8.3. Standard Services of a Local-Processing Model 8.3.1. Process a request Given a PDU, Group, LoS, and PDU-MMS, a Local Processing model must return a PDU processed according to the protocol rules defined by the Local Processing model. Harrington/Wijnen Expires November 1977 [Page 27] \ Draft Architecture for SNMPng May 1997 9. Security Consideration This document describes how the SNMPng uses a Security model and a Local Processing model to achieve a level of security for network management messages and controlled access to data. The level of security provided is determined by the specific Security model implementation(s) and the specific Local Processing model implementation(s) incorporated into this framework. 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 SNMPng engine to ensure that: 1) an implementation of this framework is fully compliant with the rules laid down by this framework, 2) the implementation of the Security model complies with the rules of the Security model, 3) the implementation of the Local Processing model complies with the rules of the Local Processing model, 4) the implementation of associated applications comply with the rules of this framework relative to applications, 5) the Security model of the implementation(s) incorporated into this framework satisfy the security needs of the organization using the SNMPng engine, 6) the Local Processing model of the implementation(s) incorporated into this framework satisfy the access control policies of the organization using the SNMPng engine, 7) the implementation of the Security model protects against inadvertently revealing security secrets in its design of implementation-specific data structures, 8) the implementation of the Local Processing model protects against inadvertently revealing configuration secrets in its design of implementation-specific data structures, 9) and the applications associated with this engine should take reasonable steps to protect the security and access control configuration secrets from disclosure. Harrington/Wijnen Expires November 1977 [Page 28] \ Draft Architecture for SNMPng May 1997 10. 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", RFC 1157, University of Tennessee at Knoxville, Performance Systems 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. [RFC1445] Galvin, J., and McCloghrie, K., "Administrative Model for version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1445, Trusted Information Systems, Hughes LAN Systems, April 1993. [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 1905, 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)", Harrington/Wijnen Expires November 1977 [Page 29] \ Draft Architecture for SNMPng May 1997 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 Internet-standard Network Management 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 Harrington/Wijnen Expires November 1977 [Page 30] \ Draft Architecture for SNMPng May 1997 11. 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: +31-348-412-498 Co-editor Dave Harrington Cabletron Systems, Inc postal: Post Office Box 5005 MailStop: Durham 35 Industrial Way Rochester NH 03867-5005 email: dbh@cabletron.com phone: 603-337-7357 Harrington/Wijnen Expires November 1977 [Page 31] \ Draft Architecture for SNMPng May 1997 12. Acknowledgements This document builds on the work of the SNMP Security and Administrative Framework Evolution team, comprised of David Harrington (Cabletron Systems Inc.) Jeff Johnson (Cisco) 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) Harrington/Wijnen Expires November 1977 [Page 32] \ Draft Architecture for SNMPng May 1997 Table of Contents 0. Change Log 2 1. Introduction 4 1.1. A Note on Terminology 4 2. Overview 5 3. An Evolutionary Architecture - Design Goals 6 3.1. Encapsulation 6 3.2. Cohesion 6 3.3. Hierarchical Rules 6 3.4. Coupling 7 4. Abstract Functionality 9 4.1. Message Processing and Control 9 4.1.1. Transport Mappings 9 4.1.2. SNMP-Based Message Formats 9 4.1.3. Application-Based Message Formats 9 4.1.4. Protocol Instrumentation 9 4.2. Security 10 4.3. Local Processing 10 4.3.1. Structure of Management Information 10 4.3.2. Textual Conventions 11 4.3.3. Conformance Statements 11 4.3.4. Protocol Operations 11 4.4. Applications 11 4.5 Coexistence 11 5. Abstract Data Elements of the Architecture 13 5.1 engineID 13 5.2. SecurityIdentity 13 5.3. Level of Security 13 5.4. Groups 13 5.5. Contexts 13 5.6. ContextEngineID 14 5.7. ContextName 14 5.8. Naming Scope 14 5.9. Scoped-PDU 14 5.10. PDU-MMS 14 5.11. Security Configuration Datastore 14 5.12. Local Configuration Datastore 14 6. Textual Conventions for the SNMPng Architecture 16 7. Model Design Requirements 19 7.1. Security Model Design Requirements 19 7.2. Local Processing Model Design Requirements 20 7.3. Message Processing and Control Requirements 21 7.4. Applications 21 7.4.1. Application Responsibilities 21 8. Subsystems and Transferring Data Between Subsystems 23 8.1. Standard Services of Message Processing and Control Models 23 8.1.1. Receive SNMP messages from the network 23 8.1.2. Send SNMP messages to the network 23 8.1.3. Coordinate the Local Processing of a Received Request Message 24 8.1.4. Forward Received Request Message to an Application 24 8.1.5. Generate a Request Message for an Application 24 8.1.6. Forward Received Response Message to an Application 25 8.1.7. Forward Received Notification Message to an Application 25 8.1.8. Send a Notification 25 8.1.9. Send a Response Message from an Application 25 8.2. Standard Services Required of Security Models 26 8.2.1. validate the security-stamp in a received message 26 8.2.2. security-stamp a message 26 8.2.3. Provide mappings between security entities and securityCookies 26 8.3. Standard Services of a Local-Processing Model 27 8.3.1. Process a request 27 9. Security Consideration 28 10. References 29 11. Editor's Addresses 31 12. Acknowledgements 32 Harrington/Wijnen Expires November 1977 [Page 33]