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Architecture for the Next Generation Simple Network Management Protocol (SNMPng) 26 April 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-00.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 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 framework, 2) a security framework, and 3) a local processing framework. Harrington/Wijnen Expires October 1977 [Page 1] \ Draft Architectural Model for SNMPng April 1997 0. Change Log [version 1.8] 1. changed filename to internet-drafts assigned name [version 1.7] 1. Truncate lines to 72 (more to be done) 2. Prepare for pagination 3. Added references section 4. Let table of contents be generated [version 1.6] 1. added abstract 2. davel's comments 3. bert's comments 4. reverted to QoS since it was less work. 5. completed section 8 6. Security Considerations, etc 7. table of contents [version 1.5] 1. add goals/constraints from issues list 2. add discussion of proxy as App 3. move ngMIB to arch from LPM doc 4. define LCD versus SCD 5. copy Bert's 2.x that apply to framework 6. modify Message definition to better match Bert's ASN.1 [version 1.4] 1. modified intro 2. added section on design principles/goals 3. added section on message contents and service interfaces 4. defined LP-F versus LP-M 5. changed QoS to msgFlags [version 1.3] 1. modified title from Security and Framework Evolution to Next Generation 2. expanded section 4 - architectural design goals 3. replaced all acronyms with the new acronyms Harrington/Wijnen Expires October 1977 [Page 2] \ Draft Architectural Model for SNMPng April 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. 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 a framework which can evolve to realize effective SNMP network management in a variety of configurations and environments. The framework 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 For the purpose of exposition, the original Internet-standard Network Management Framework, as described in RFCs 1155, 1157, and 1212, is termed the SNMP version 1 framework (SNMPv1). A partially-updated Internet-standard Network Management framework , as described in RFCs 1902-1908, is termed the SNMP version 2 framework (SNMPv2). The current framework, meant to complement the SNMPv2 framework, is termed the SNMP next generation framework (SNMPng). SNMPng provides a framework for the evolution of multiple (sub-)frameworks. Throughout the rest of this document, the term Framework 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 Framework, 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 Framework, conforming to a specific Model. Harrington/Wijnen Expires October 1977 [Page 3] \ Draft Architectural Model for SNMPng April 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. 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 October 1977 [Page 4] \ Draft Architectural Model for SNMPng April 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. Harrington/Wijnen Expires October 1977 [Page 5] \ Draft Architectural Model for SNMPng April 1997 The SNMPng architecture uses the hierarchical approach by defining frameworks, 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 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. Cross-references between document describing the subsystems should be limited to Framework or Model defined interfaces wherever possible. Loose coupling works well with the IETF standards process. If we separate message-handling from security and from local processing, 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 October 1977 [Page 6] \ Draft Architectural Model for SNMPng April 1997 4.0. Abstract Functionality The architecture described here is composed of four "major" frameworks, each capable of being defined as different models, and which may be implemented as modules which can be replaced or supplemented as the growing needs of network management require. The major frameworks are a Message Processing and Control Framework, a Security Framework, a Local Processing Framework, and Applications. Interfaces between the major frameworks are deliberately abstract and fixed. An SNMPng engine is comprised of implementations of a Message Processing and Control Framework, a Security Framework, and a Local Processing Framework. Applications are external to the engine. 4.1. Message Processing and Control An SNMP engine interacts with the network and with applications through the Message Processing and Control Framework. Messages being sent to, or received from, the network use a format defined by the SNMP protocol. The possible contents, and their format, are also defined by the SNMP protocol. Messages being sent to, or received from, applications use formats which may be protocol-defined or may be implementation-specific. The possible contents, and their format, may be protocol-defined or implementation-specific. The processing of messages must be controlled to ensure that applicable rules are followed during the processing. Some messages, such as an SNMP Get-Request received from the network for objects managed by this engine, can be processed directly by the engine; other messages must be passed to external processes, such as a remote SNMP engine or an application. Some messages require security; others don't. Some engines support multiple versions of SNMP messages and/or PDU formats. The engine must control the order and the combinations of options used in processing and generating messages. 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. Harrington/Wijnen Expires October 1977 [Page 7] \ Draft Architectural Model for SNMPng April 1997 4.3. Local Processing Local Processing deals with the contents of messages. It interacts with the underlying operating system to access the instrumentation which is represented as managed objects in SNMP. 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 entity on whose behalf a request is generated. 4.4. Applications Applications are processes which interact with the SNMP engine using messages that may use formats defined by a protocol, or that may use implementation-specific formats. Applications are developed to achieve certain goals. They use the SNMP engine to achieve their goals, but their purpose is outside the scope of the SNMP protocol definitions. For example, management stations execute applications which monitor and control managed elements. A proxy application may forward a message from one SNMP engine to another (an snmp proxy), or convert a message from one SNMP format to another (also an snmp proxy), or from SNMP to another protocol ( a foreign proxy). The purpose and design of applications are beyond the scope of the SNMPng engine architecture. 4.5. Definition of SNMPng acronyms and terms: MPC-F - Message Processing and Control Framework MPC-M - Message Processing and Control Model MPC-I - Message Processing and Control Implementation SF-F - Security Framework SF-M - Security Framework Model SF-I - Security Framework Implementation LP-F - Local Processing Framework LP-M - Local Processing Model LP-I - Local Processing Implementation LCD - Local Configuration Datastore SCD - Security Configuration Datastore Harrington/Wijnen Expires October 1977 [Page 8] \ Draft Architectural Model for SNMPng April 1997 5. Elements of the Framework This section contains definitions of terms used in the interfaces between Frameworks 5.1. Groups A Group identifies a set of zero or more security entities on whose behalf SNMP messages are being processed. 5.2. Quality of Service Messages may require different levels of security. The term used to refer to the level of security required is "Quality of Service" or QoS. 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 QoS; all processing (security, access control, applications, message processing and control) is required to abide the specified QoS. 5.3. Contexts An SNMP context is a collection of management information accessible by an SNMP agent. An item of management information may exist in more than one context. An SNMP agent potentially has access to many contexts. 5.4. Scoped-PDU A scoped-PDU contains a Naming-Scope that unambiguously identifies an SNMP agent and the context, (locally) accessible by that agent, to which the SNMP management information in the SNMP-PDU refers. A Naming-Scope contains a contextID that unambiguously identifies the SNMP agent which has (local) access to the management information referred to by the contextName and the SNMP-PDU. A Naming-Scope contains a contextName which unambiguously identifies an SNMP context accessible by the SNMP agent to which the SNMP-PDU is directed or from which the SNMP-PDU is originated. An implementation of a Message Processing and Control Model must determine if the contextID in the scopedPDU of a received message matches the snmpNgEngineID of the current engine. If so, the scopedPDU should be processed by the Local Processing implementation. Harrington/Wijnen Expires October 1977 [Page 9] \ Draft Architectural Model for SNMPng April 1997 5.5. Security Configuration Datastore Each Security Model may need to retain its own set of information about security entities, mechanisms, and policies. This set of information is called the SNMPng entity's Security Configuration Datastore (SCD). In order to allow an SNMPng entity's SCD to be remotely configured, portions may need to be accessible as managed objects. 5.6. Local Configuration Datastore Each Local Processing Model may need to retain its own set of information about access control, naming scopes, and policies. This set of information is called the SNMPng entity's Local Processing Configuration Datastore (LCD). In order to allow an SNMPng entity's LCD to be remotely configured, portions may need to be accessible as managed objects. Harrington/Wijnen Expires October 1977 [Page 10] \ Draft Architectural Model for SNMPng April 1997 6. 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. 6.1. Security Model Design Requirements Received messages must be validated by a model of the Security Framework before being processed by the Local Processing Framework. 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 Quality of Service 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 is restricted to using the interface, defined in this document, between the Message Processing and Control Framework and the Security Framework. 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 QoS and the security parameters passed in 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. Security Models are replaceable within the SNMPng Framework. 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 entity within the model's SCD, and a securityCookie. A securityCookie Harrington/Wijnen Expires October 1977 [Page 11] \ Draft Architectural Model for SNMPng April 1997 is an implementation-specific handle to identify the unique entity 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 security entity. 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 MIBs required for security processing, including any MIBs required for the protocol(s) supported. The MIB formats must be defined concurrently with the procedures which use the MIB. The MIBs 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 security entity 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. Within any Security Model, there should be no reference to any specific Local Processing Model, or to data defined by a Local Processing Model. 6.2. Local Processing Model Design Requirements A Local processing Model only processes scopedPDUs which contain a contextID which matches the engineID of the current engine. A Local Processing Model must determine whether the specified group is allowed to perform the requested operation on the managed objects in the PDU. For messages with a QoS specifying authentication, the group used for access control must be the same group provided by the Message Processing and Control Framework. 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 restricted to using the interface, defined in this document, between the Message Processing and Control Framework and the Local Processing Framework. Harrington/Wijnen Expires October 1977 [Page 12] \ Draft Architectural Model for SNMPng April 1997 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. Within any Local Processing Model, there should be no reference to any specific Security Model, or any data defined by a Security Model. 6.3. Message Processing and Control Requirements The MPC Model must always pass the complete scopedPDU, i.e. it never forwards less than the complete list of varbinds. The MPC Model must determine whether a scopedPDU should be processed by the current engine or by an application. If a received message contains a scopedPDU with a contextID matching the engineID of the current engine, then the scopedPDU should be passed to the Local Processing Model implementation for processing. If the MPC Model determines that the contextID does not match the engineID of the current engine, then the message parts, as specified in the interface section, are passed to a proxy application for processing. 6.4. Applications Applications are beyond the scope of this document, but earlier attempts to define an SNMP Framework considered proxy as a possible function of the protocol. SNMPng does not mandate support for proxy in an SNMPng implementation. 6.4.1. A Proxy Application The SNMPng Framework explicitly considers proxy to be an external application. There are certain issues that must be clarified regarding the relation and interface between proxy and the engine, however. A proxy application has the responsibility to define any MIBs used to forward message contents, and to determine the address and identity to whom the message should be forwarded. An engine supports at most one interface to proxy applications; if an implementation wishes to support multiple proxy applications, the determination of which type of proxy, and hence which proxy application should handle it, should be handled by the single proxy application to which the engine has an interface. If proxy is supported, the engine passes all scopedPDUs with a contextID that does not match the current engine's snmpNgEngineID to the proxy application. No access control is applied to the message by the engine which passes the request to the proxy application. A scopedPDU passed to a proxy application must be a complete scopedPDU. Harrington/Wijnen Expires October 1977 [Page 13] \ Draft Architectural Model for SNMPng April 1997 Harrington/Wijnen Expires October 1977 [Page 14] \ Draft Architectural Model for SNMPng April 1997 7. The SNMPng message format: DEFINITIONS ::=3D BEGIN snmpNgMessage ::=3D SEQUENCE { -- global parameters version INTEGER { snmpng (3) }, msgID INTEGER, MMS INTEGER, QoS OCTET STRING (SIZE(1)), -- .... ..00 noAuth/noPriv -- .... ..01 auth/noPriv -- .... ..1. auth/priv -- .... .1.. reportableFlag securityModel snmpNgSecurityModel, -- security model-specific parameters securityParameters OCTET STRING, -- format defined by Security Model -- local-processing model-specific data data ScopedPduData } ScopedPduData ::=3D CHOICE { plaintext ScopedPDU, encrypted OCTET STRING -- encrypted ScopedPDU } scopedPDU ::=3D SEQUENCE { contextID snmpNgEngineID, contextName snmpNgContextName, data ANY -- e.g. PDUs as defined in RFC1905 } END Harrington/Wijnen Expires October 1977 [Page 15] \ Draft Architectural Model for SNMPng April 1997 7.1. SNMP version The SNMP version identifies the version of the MPC framework in use. For purposes of discouraging, but not preventing, the replacement of the Local Processing Model, the SNMP version also implies the version of the Local Processing Model. 7.2. msgID The msgID is used by SNMP engines to coordinate the processing of the message by different portions of the framework. Note that the requestID used during local processing identifies the request, not the message that carried the request, and therefore might not be equal to the msgID. 7.3. MMS The maximum message size supported by the sender of the message. 7.4. securityModel Multiple security models may exist concurrently in the engine. This model number identifies which security model should be used to provide security processing for the message. The mapping to the appropriate implementation within the agent is done in an implementation-dependent manner. The initial model of the SNMPng Security Framework is the User-Based Security Model of the SNMPng Security Framework. 7.5. QoS The QoS field contains flags to control the processing of the message. If the reportableFlag is set, then reportPDUs are allowed to be returned to the sender under those conditions which cause the generation of reportPDUs. If the reportableFlag is zero, then a reportPDU must not be sent. The reportableFlag should always be zero when the message is a reportPDU, a responsePDU, or a trapPDU. If the auth flag is set, then the security implementation is required to identify the entity on whose behalf a request is generated and to authenticate such identification. If the auth flag is zero, authentication of the identification is not required. If the priv flag is set, then the security implementation is required to protect the data within an SNMP operation from disclosure, i.e. to encrypt the data. If the priv flag is zero, then the security Harrington/Wijnen Expires October 1977 [Page 16] \ Draft Architectural Model for SNMPng April 1997 implementation does not need to protect the data using encryption. It is an explicit requirement of the SNMPng Framework that if privacy is selected, then authentication of the identification is required, i.e. priv flag can only be set if auth flag is also set. 7.6. security parameters This octet string is not interpreted by the MPC-F. This data is used exclusively by the security model, and the contents and format of the data is defined by the security model. 7.7. scopedPDU The scopedPDU contains a PDU and the scope in which it is to be processed, as defined by the ID of the engine and the context within which the management data is realized on that engine. 7.7.1. contextID This is the engineID of the engine which realizes the managed objects referenced in the PDUs. 7.7.2. contextName This is the name of the context, on the contextID-specified engine, which realizes the managed objects referenced within the PDUs. 7.7.3. data The data contains the PDUs. The Local Processing Model defines the content and format of the PDUs. The initial model of the SNMPng Local Processing Framework supports SNMPv2 PDUs as defined in RFC1905. Harrington/Wijnen Expires October 1977 [Page 17] \ Draft Architectural Model for SNMPng April 1997 8. The Frameworks and their standard "services" interfaces Each Framework defines certain standard services, accessible through protocol-fixed interfaces. Each Model for a Framework must provide the standard services, but how it performs the service is defined by the model. 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, an MPC-M will extract the MMS, and the QoS, and will determine where the block of security parameters start in the message. It 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 MPC-M will pass the MMS, the QoS, a pointer to the message, and a pointer to the block of security parameters to the implementation of the Security Model specified in the message header. The Security Model, after completion of its processing, will return to the Message Processing and Control implementation the group, the securityCookie, the scopedPDU-MMS, and the scopedPDU. 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 MPC-M will pass a scopedPDU, the securityCookie, and all global data to be included in the message to the Security Model. The Security Model will construct the message, and return the completed message to the MPC-M, will 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 MPC will receive the SNMP message according to the process described in 8.1.1. The Message Processing and Control implementation will compare the contextID in the scopedPDU with its snmpNgEngineID. If they match, the MPC will forward the scopedPDU to the Local Processing implementation. The MPC will pass the scopedPDU, the Group, and the scopedPDU-MMS provided by the Security Model implementation, plus the QoS, to the Local Processing implementation. Harrington/Wijnen Expires October 1977 [Page 18] \ Draft Architectural Model for SNMPng April 1997 It will accept a completed scopedPDU containing the responsePDU from the LP-I, and generate a response message according to the process described in 8.1.2. 8.1.4. Forward Received Request Message to a Proxy Application The MPC will receive the SNMP message according to the process described in 8.1.1. The MPC will determine whether a scopedPDU in a received message contains a contextID which differs from its snmpNgEngineID. If it does differ, and if a proxy application is supported by this engine, the MPC will assign an implementation-defined handle to the message. The MPC will determine, from the message header, the SNMP version, the securityModel, the MMS, and the QoS. It will pass to the proxy application the handle, the SNMP version, securityModel, MMS, QoS, plus the securityCookie provided by the Security Model implementation. 8.1.5. Generate a Request Message for an Application The MPC will receive a request for the generation of a request message from an application. The application has the responsibility for providing the Destination Address, the SNMP version, the QoS desired, the MMS of the current engine, the SecurityModel to use, 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 MPC checks the verb in the scopedPDU to determine that it is a request message, and if so, skips local processing of the scopedPDU. The MPC will generate the message according to the process described in 8.1.2. 8.1.6. Forward Received Response Message to an Application The MPC will receive the SNMP message according to the process described in 8.1.1. The MPC will determine which application is awaiting a response, using the handle assigned to the transaction in step 8.1.3 The MPC will pass to the application the QoS, the MMS, the Security Model, the securityCookie, the scopedPDU-MMS, and the scopedPDU. The Application, using the securityCookie, will determine the end-user on whose behalf the response should be processed. Harrington/Wijnen Expires October 1977 [Page 19] \ Draft Architectural Model for SNMPng April 1997 8.1.7. Forward Received Notification Message to an Application The MPC will receive the SNMP message according to the process described in 8.1.1. The MPC will determine to which application traps should be forwarded. The MPC will pass to the application the QoS, the MMS, the Security Model, the securityCookie, the scopedPDU-MMS, and the scopedPDU. The Application, using the securityCookie, will determine the end-user on whose behalf the notification should be processed. 8.1.8. Generate a Trap Message The MPC accepts from the LP-I a Destination Address, the QoS, the SecurityModel, the Group, and the scopedPDU. The MPC uses the group and QoS to request a list of securityCookies from the Security Model for security entities contained in the group. For each securityCookie in the list, the MPC generates an SNMP message according to the process described in 8.1.2. 8.1.9. Send a Response Message from a Proxy Application The MPC will send the SNMP message according to the process described in 8.1.1. The MPC will determine which application is awaiting a response, using the handle assigned to the transaction in step 8.1.3 The MPC will pass to the application the QoS, the MMS, the Security Model, the securityCookie, the scopedPDU-MMS, and the scopedPDU. The Application, using the securityCookie, will determine the end-user on whose behalf the response should be processed. 8.2. Standard Services Required of Security Models 8.2.1. validate the security-stamp in a received message given a message, the MMS, QoS, and the security parameters from that message, verify the message has not been altered, and authenticate the identification of the security entity for whom the message was generated. If encrypted, decrypt the message additional requirements may be defined by the model, but they cannot require changes to the framework interface Harrington/Wijnen Expires October 1977 [Page 20] \ Draft Architectural Model for SNMPng April 1997 return a securityCookie identifying the entity for whom the message was generated and return the portions of the message needed for further processing: a scopedPDU - a PDU enclosed by a header which contains an snmpID and a contextName QoS - the quality of service specified for security validation. The same quality of service 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. scopedPDU-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. acGroup - the acGroup to be applied for access control for the entity for whom the request was generated. 8.2.2. security-stamp a message Given a scopedPDU, QoS, 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 Given model-specific parameters to identify a security entity, an SF-M must return a securityCookie Given a securityCookie generated by this SF-M, the SF-M must return model-specific data identifying the corresponding security entity. 8.2.4. Provide mapping between group and securityCookies Given a group, the SF-M must return an array of securityCookies identifying the entities which are members of the specified group. 8.3. Standard Services of a Local-Processing Model 8.3.1. Process a request Given a ScopedPDU, Group, QoS, and ScopedPDU-MMS, an LP-M must return a scopedPDU processed according to the protocol rules of the LP-M 8.3.2. Generate a Trap When an event occurs that requires the generation of a trap, the LP-M must pass to the MPC a Destination Address, QoS, MMS, SecurityModel, a Group, and a scopedPDU, according to the protocol rules of the LP-M. Harrington/Wijnen Expires October 1977 [Page 21] \ Draft Architectural Model for SNMPng April 1997 Harrington/Wijnen Expires October 1977 [Page 22] \ Draft Architectural Model for SNMPng April 1997 9. Definitions 9.1. Definitions for the Architectural Model for SNMPng snmpNg-MIB DEFINITIONS ::=3D 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: 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 " DESCRIPTION "The snmpNg engine MIB" ::=3D { snmpModules xx } -- Administrative assignments snmpNgMIBObjects OBJECT IDENTIFIER ::=3D { snmpNgMIB 1 } Harrington/Wijnen Expires October 1977 [Page 23] \ Draft Architectural Model for SNMPng April 1997 snmpNgMIBConformance OBJECT IDENTIFIER ::=3D { snmpNgMIB 2 } -- Textual Conventions used throughout the SNMPng Framework snmpNgGroupName ::=3D TEXTUAL-CONVENTION STATUS current DESCRIPTION "An octet string representing the name of a group for use in accordance with the SNMPng Architectural Framework. " SYNTAX OCTET STRING (SIZE(1..16)) snmpNgContextName ::=3D TEXTUAL-CONVENTION STATUS current DESCRIPTION "An SNMPng context name which unambiguously identifies a set of management information directly accessible by the Local Processing Module (implementation or LP-I) of an SNMPng engine. " SYNTAX OCTET STRING (SIZE (0..32)) snmpNgQoS ::=3D TEXTUAL-CONVENTION STATUS current DESCRIPTION "A level of security at which SNMPng 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) } snmpNgEngineID ::=3D TEXTUAL-CONVENTION STATUS current DESCRIPTION "An SNMPng entity'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. Harrington/Wijnen Expires October 1977 [Page 24] \ Draft Architectural Model for SNMPng April 1997 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)) snmpNgSecurityModel ::=3D TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identifier that uniquely identifies an SNMPng Security Model within the SNMPng Framework. " SYNTAX INTEGER -- SNMPng MIB objects implemented by the SNMPng MPC ****************** snmpNgEngineID OBJECT-TYPE SYNTAX snmpNgEngineID MAX-ACCESS read-only STATUS current DESCRIPTION "The SNMPng entity's administratively-unique SNMP-Engine identifier. " ::=3D { snmpNgMIBObjects 1 } snmpNgEngineMms OBJECT-TYPE SYNTAX INTEGER MAX-ACCESS read-only STATUS current DESCRIPTION "The maximum length in octets of an SNMPng message which this SNMPng entity will accept using any transport mapping. " ::=3D { snmpNgMIBObjects 2 } -- Conformance information snmpNgMIBCompliances OBJECT IDENTIFIER ::=3D { snmpNgMIBConformance 1 } snmpNgMIBGroups OBJECT IDENTIFIER ::=3D { snmpNgMIBConformance 2 } Harrington/Wijnen Expires October 1977 [Page 25] \ Draft Architectural Model for SNMPng April 1997 -- Compliance statements snmpNgMIBCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMPng entities which implement the SNMPng (MPC) remote configuration MIB. " MODULE -- this module MANDATORY-GROUPS { snmpNgBasicGroup } ::=3D { snmpNgMIBCompliances 1 } snmpNgBasicGroup OBJECT-GROUP OBJECTS { snmpNgEngineID, snmpNgEngineMms } STATUS current DESCRIPTION "A collection of objects providing for remote configuration of an SNMPng entity which implements the SNMPng MPC-Model. " ::=3D { snmpNgMIBGroups 1 } END Harrington/Wijnen Expires October 1977 [Page 26] \ Draft Architectural Model for SNMPng April 1997 10. Agent Installation Parameters During installation, an SNMPng entity acting in an agent role is configured with several parameters. These include: (1) a security posture The choice of security posture determines the extent of the view configured for unauthenticated access. One of three possible choices is selected: minimum-secure, semi-secure, or very-secure. (2) one or more transport service addresses These parameters may be specified explicitly, or they may be specified implicitly as the same set of network-layer addresses configured for other uses by the device together with the well- known transport-layer "port" information for the appropriate transport domain 13. The agent listens on each of these transport service addresses for messages. Harrington/Wijnen Expires October 1977 [Page 27] \ Draft Architectural Model for SNMPng April 1997 11. 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 actually provided is primarily 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 October 1977 [Page 28] \ Draft Architectural Model for SNMPng April 1997 12. References [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. [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 Internet-standard Network Management Framework", RFC 1908, January 1996. [SNMPng-ARCH] The SNMPng Working Group, Harrington, D., Wijnen, B., "Architecture for the Next Generation Simple Network Management Protocol (SNMPng)", draft-ietf-snmpv3-next-gen-arch-00.txt, April 1997. [SNMPng-LPM] The SNMPng Working Group, Wijnen, B., Harrington, D., "Local Processing Model for the Next Generation Simple Network Management Protocol (SNMPng)", draft-ietf-snmpng-lpm-00.txt, April 1997. [SNMPng-USEC] To be written The SNMPng Working Group, Editors...Names, "The User-Based Security Model for the Next Generation Simple Network Management Protocol (SNMPng)", draft-ietf-snmpng-usec-00.txt, April 1997. Harrington/Wijnen Expires October 1977 [Page 29] \ Draft Architectural Model for SNMPng April 1997 13. 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 14. Acknowledgements This document describes 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 October 1977 [Page 30] \ Draft Architectural Model for SNMPng April 1997 Table of Contents 0. Change Log 2 1. Introduction 3 1.1. A Note on Terminology 3 2. Overview 4 3. An Evolutionary Architecture - Design Goals 5 3.1. Encapsulation 5 3.2. Cohesion 5 3.3. Hierarchical Rules 5 3.4. Coupling 6 4.0. Abstract Functionality 7 4.1. Message Processing and Control 7 4.2. Security 7 4.3. Local Processing 8 4.4. Applications 8 4.5. Definition of SNMPng acronyms and terms: 8 5. Elements of the Framework 9 5.1. Groups 9 5.2. Quality of Service 9 5.3. Contexts 9 5.4. Scoped-PDU 9 5.5. Security Configuration Datastore 10 5.6. Local Configuration Datastore 10 6. Model Design Requirements 11 6.1. Security Model Design Requirements 11 6.2. Local Processing Model Design Requirements 12 6.3. Message Processing and Control Requirements 13 6.4. Applications 13 6.4.1. A Proxy Application 13 7. The SNMPng message format: 15 7.1. SNMP version 16 7.2. msgID 16 7.3. MMS 16 7.4. securityModel 16 7.5. QoS 16 7.6. security parameters 17 7.7. scopedPDU 17 7.7.1. contextID 17 7.7.2. contextName 17 7.7.3. data 17 8. The Frameworks and their standard "services" interfaces 18 8.1. Standard Services of Message Processing and Control Models 18 8.1.1. Receive SNMP messages from the network 18 8.1.2. Send SNMP messages to the network 18 8.1.3. Coordinate the Local Processing of a Received Request Message 18 8.1.4. Forward Received Request Message to a Proxy Application 19 8.1.5. Generate a Request Message for an Application 19 8.1.6. Forward Received Response Message to an Application 19 8.1.7. Forward Received Notification Message to an Application 20 8.1.8. Generate a Trap Message 20 8.1.9. Send a Response Message from a Proxy Application 20 8.2. Standard Services Required of Security Models 20 8.2.1. validate the security-stamp in a received message 20 8.2.2. security-stamp a message 21 8.2.3. Provide mappings between security entities and securityCookies 21 8.2.4. Provide mapping between group and securityCookies 21 8.3. Standard Services of a Local-Processing Model 21 8.3.1. Process a request 21 8.3.2. Generate a Trap 21 9. Definitions 23 9.1. Definitions for the Architectural Model for SNMPng 23 10. Agent Installation Parameters 27 11. Security Consideration 28 12. References 29 13. Editor's Addresses 30 14. Acknowledgements 30 Harrington/Wijnen Expires October 1977 [Page 31]