RFC 2271
An Architecture for Describing SNMP Management Frameworks
RFC 2271 ✨ An Architecture for Describing SNMP Management Frameworks
okay bestie, this one is RFC 2271 🦋 It's from the Network Working Group and was written by D. Harrington (Cabletron Systems, Inc.), R. Presuhn (BMC Software, Inc.), and B. Wijnen (IBM T. J. Watson Research). It's dated January 1998 and its category is Standards Track 🎀
It obsoletes RFC 2261, so that's the older version it replaces. The header doesn't list any RFC it updates.
Status of this Memo
so this part is the official status stuff 💅 This document specifies an Internet standards track protocol for the Internet community, and it asks for discussion and suggestions for improvements. For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited 🌸
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved. 🔒
IANA Note
ok so there was a clerical error in how the snmpModules got assigned in the earlier memo 🙈 This RFC gives the corrected number assignment for this protocol, and it obsoletes RFC 2261. Iconic recovery arc ngl 🍓
Abstract
this doc describes an architecture for describing SNMP Management Frameworks ✨ It's designed to be modular so SNMP protocol standards can evolve over time 🧚 The major pieces are an SNMP engine that contains a Message Processing Subsystem, a Security Subsystem, and an Access Control Subsystem. There can also be multiple SNMP applications that do specific functional processing of management data. It's giving well-organized 👑
Table of Contents
1. Introduction ................................................ 3
1.1. Overview .................................................. 3
1.2. SNMP ...................................................... 4
1.3. Goals of this Architecture ................................ 5
1.4. Security Requirements of this Architecture ................ 6
1.5. Design Decisions .......................................... 7
2. Documentation Overview ...................................... 8
2.1. Document Roadmap .......................................... 10
2.2. Applicability Statement ................................... 10
2.3. Coexistence and Transition ................................ 10
2.4. Transport Mappings ........................................ 11
2.5. Message Processing ........................................ 11
2.6. Security .................................................. 11
2.7. Access Control ............................................ 11
2.8. Protocol Operations ....................................... 12
2.9. Applications .............................................. 12
2.10. Structure of Management Information ...................... 12
2.11. Textual Conventions ...................................... 13
2.12. Conformance Statements ................................... 13
2.13. Management Information Base Modules ...................... 13
2.13.1. SNMP Instrumentation MIBs .............................. 13
2.14. SNMP Framework Documents ................................. 13
3. Elements of the Architecture ................................ 14
3.1. The Naming of Entities .................................... 14
3.1.1. SNMP engine ............................................. 15
3.1.1.1. snmpEngineID .......................................... 16
3.1.1.2. Dispatcher ............................................ 16
3.1.1.3. Message Processing Subsystem .......................... 16
3.1.1.3.1. Message Processing Model ............................ 17
3.1.1.4. Security Subsystem .................................... 17
3.1.1.4.1. Security Model ...................................... 17
3.1.1.4.2. Security Protocol ................................... 18
3.1.2. Access Control Subsystem ................................ 18
3.1.2.1. Access Control Model .................................. 18
3.1.3. Applications ............................................ 18
3.1.3.1. SNMP Manager .......................................... 19
3.1.3.2. SNMP Agent ............................................ 20
3.2. The Naming of Identities .................................. 21
3.2.1. Principal ............................................... 21
3.2.2. securityName ............................................ 21
3.2.3. Model-dependent security ID ............................. 22
3.3. The Naming of Management Information ...................... 22
3.3.1. An SNMP Context ......................................... 23
3.3.2. contextEngineID ......................................... 24
3.3.3. contextName ............................................. 24
3.3.4. scopedPDU ............................................... 25
3.4. Other Constructs .......................................... 25
3.4.1. maxSizeResponseScopedPDU ................................ 25
3.4.2. Local Configuration Datastore ........................... 25
3.4.3. securityLevel ........................................... 25
4. Abstract Service Interfaces ................................. 26
4.1. Dispatcher Primitives ..................................... 26
4.1.1. Generate Outgoing Request or Notification ............... 26
4.1.2. Process Incoming Request or Notification PDU ............ 26
4.1.3. Generate Outgoing Response .............................. 27
4.1.4. Process Incoming Response PDU ........................... 27
4.1.5. Registering Responsibility for Handling SNMP PDUs ....... 28
4.2. Message Processing Subsystem Primitives ................... 28
4.2.1. Prepare Outgoing SNMP Request or Notification Message ... 28
4.2.2. Prepare an Outgoing SNMP Response Message ............... 29
4.2.3. Prepare Data Elements from an Incoming SNMP Message ..... 29
4.3. Access Control Subsystem Primitives ....................... 30
4.4. Security Subsystem Primitives ............................. 30
4.4.1. Generate a Request or Notification Message .............. 30
4.4.2. Process Incoming Message ................................ 31
4.4.3. Generate a Response Message ............................. 31
4.5. Common Primitives ......................................... 32
4.5.1. Release State Reference Information ..................... 32
4.6. Scenario Diagrams ......................................... 32
4.6.1. Command Generator or Notification Originator ............ 32
4.6.2. Scenario Diagram for a Command Responder Application .... 33
5. Managed Object Definitions for SNMP Management Frameworks ... 35
6. Intellectual Property ....................................... 44
7. Acknowledgements ............................................ 45
8. Security Considerations ..................................... 46
9. References .................................................. 46
10. Editors' Addresses ......................................... 48
A. Guidelines for Model Designers .............................. 49
A.1. Security Model Design Requirements ........................ 49
A.1.1. Threats ................................................. 49
A.1.2. Security Processing ..................................... 50
A.1.3. Validate the security-stamp in a received message ....... 51
A.1.4. Security MIBs ........................................... 51
A.1.5. Cached Security Data .................................... 51
A.2. Message Processing Model Design Requirements .............. 52
A.2.1. Receiving an SNMP Message from the Network .............. 52
A.2.2. Sending an SNMP Message to the Network .................. 52
A.3. Application Design Requirements ........................... 53
A.3.1. Applications that Initiate Messages ..................... 53
A.3.2. Applications that Receive Responses ..................... 54
A.3.3. Applications that Receive Asynchronous Messages ......... 54
A.3.4. Applications that Send Responses ........................ 54
A.4. Access Control Model Design Requirements .................. 55
B. Full Copyright Statement .................................... 561. Introduction 📖
1.1. Overview
so this doc is basically a vocabulary for describing SNMP Management Frameworks, plus an architecture for describing the big chunks of those frameworks 🎀
it does NOT give you a general intro to SNMP, and it doesn't give you SNMP history either. other docs and books are way better for that 🙈
here's how the rest of the doc is laid out 🗺️
- Section 1 covers the purpose, goals, and design decisions of this architecture.
- Section 2 covers the different types of documents that define SNMP Frameworks and how they fit in here. It also gives a minimal roadmap to the docs that already defined SNMP frameworks.
- Section 3 lays out the vocabulary of this architecture and its pieces. This one is super important for the rest of the doc and for any docs written to fit this architecture 🧠
- Section 4 describes the primitives used for the abstract service interfaces between the various subsystems, models, and applications.
- Section 5 defines a collection of managed objects used to instrument SNMP entities in this architecture.
- Sections 6, 7, 8, and 9 are administrative in nature 📋
- Appendix A has guidelines for designers of Models that are expected to fit this architecture 🛠️
and last but not least, the key words are the requirement-level words that matter 🔑 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] 💜
more to come, bestie 🫶
1.2. SNMP ✨
okay so an SNMP management system is basically a group chat with a few key roles 💅
- several (potentially many) nodes, each with an SNMP entity 🫶 that holds command responder and notification originator applications. These have access to the management instrumentation (traditionally called agents) 🌸
- at least one SNMP entity running command generator and/or notification receiver applications (traditionally called a manager) 👑 and,
- a management protocol, which is how the SNMP entities pass management information back and forth 💌
the SNMP entities running the command generator and notification receiver apps are the ones doing the monitoring and controlling 🎀 and the managed elements are things like hosts, routers, terminal servers, etc. 🖥️ they get watched and tweaked through access to their management information 👀
the whole point of this document is to define an architecture that can grow and glow up 🌈 so it can handle effective management in all kinds of setups and environments. it was designed to meet the needs of implementations of:
- minimal SNMP entities with command responder and/or notification originator applications (traditionally called SNMP agents) 🧚
- SNMP entities with proxy forwarder applications (traditionally called SNMP proxy agents) 🦋
- command line driven SNMP entities with command generator and/or notification receiver applications (traditionally called SNMP command line managers) 💻
- SNMP entities with command generator and/or notification receiver, plus command responder and/or notification originator applications (traditionally called SNMP mid-level managers or dual-role entities) ✨
- SNMP entities with command generator and/or notification receiver and possibly other types of applications for managing a potentially very large number of managed nodes (traditionally called (network) management stations) 🏰
1.3. Goals of this Architecture
this architecture had a whole list of goals, and honestly they're giving main character energy 💖
- Use existing materials as much as possible. it's heavily based on earlier work, informally known as SNMPv2u and SNMPv2* 🍓
- Address the need for secure SET support, which is considered the most important deficiency in SNMPv1 and SNMPv2c 🔐 this one is lowkey the big one 😭
- Make it possible to move portions of the architecture forward in the standards track, even if consensus hasn't been reached on all pieces 🛤️
- Define an architecture that allows for longevity of the SNMP Frameworks that have been and will be defined 🦋
- Keep SNMP as simple as possible. simple is iconic 💅
- Make it relatively inexpensive to deploy a minimal conforming implementation. 💸
- Make it possible to upgrade portions of SNMP as new approaches become available, without disrupting an entire SNMP framework 🔄
- Make it possible to support features required in large networks, but make the expense of supporting a feature directly related to the support of the feature. so you only pay for what you actually use, no cap 🧾
1.4. Security Requirements of this Architecture
okay this part is where it gets serious 🥺 several of the classic threats to network protocols apply to the management problem, so they'd apply to any Security Model used in an SNMP Management Framework too. other threats don't apply to management at all. this section talks about principal threats, secondary threats, and the threats that matter less 🔍
the principal threats that any Security Model used within this architecture SHOULD provide protection against are:
- Modification of Information the modification threat is the danger that some unauthorized SNMP entity alters in-transit SNMP messages generated on behalf of an authorized principal, in a way that causes unauthorized management operations, including falsifying the value of an object 😱
- Masquerade the masquerade threat is the danger that management operations not authorized for some principal get attempted by pretending to be another principal who has the right authorizations 🎭
- Message Stream Modification SNMP is typically based on a connectionless transport service, which may operate over any subnetwork service. re-ordering, delay or replay of messages can and does happen through the normal operation of many subnetwork services. the message stream modification threat is the danger that messages get maliciously re-ordered, delayed or replayed to a greater extent than normal subnetwork operation could cause, in order to pull off unauthorized management operations 🌀
- Disclosure the disclosure threat is the danger of eavesdropping on the exchanges between SNMP engines. protecting against this threat may be required as a matter of local policy 👂
there are at least two threats that a Security Model within this architecture doesn't need to protect against:
- Denial of Service a Security Model doesn't need to try to address the broad range of attacks that deny service to authorized users. honestly these denial-of-service attacks often look exactly like the network failures any viable management protocol has to cope with anyway 🙄
- Traffic Analysis a Security Model doesn't need to address traffic analysis attacks. many traffic patterns are predictable (entities may be managed on a regular basis by a relatively small number of management stations), so protecting against traffic analysis wouldn't give any significant advantage 📊
1.5. Design Decisions
a bunch of design decisions were made to support the goals of the architecture and the security requirements 🎀
- Architecture an architecture should be defined that identifies the conceptual boundaries between the documents. subsystems should be defined that describe the abstract services provided by specific portions of an SNMP framework. abstract service interfaces, described by service primitives, define the abstract boundaries between documents and the abstract services provided by the conceptual subsystems of an SNMP framework 🗺️
- Self-contained Documents the elements of procedure plus the MIB objects needed for processing a specific portion of an SNMP framework should be defined in the same document, and as much as possible should not be referenced in other documents. this lets pieces be designed and documented as independent, self-contained parts, which fits the general SNMP MIB module approach 🧩 when parts of SNMP change over time, the documents describing other portions aren't directly impacted. this modularity means things like Security Models, authentication and privacy mechanisms, and message formats can be upgraded and supplemented as needed 🔧 these self-contained documents can move along the standards track on different timelines 🕰️
- Threats the Security Models in the Security Subsystem SHOULD protect against the principal threats: modification of information, masquerade, message stream modification and disclosure. they don't need to protect against denial of service and traffic analysis 🛡️
- Remote Configuration the Security and Access Control Subsystems add a whole new set of SNMP configuration parameters 😵💫 the Security Subsystem also requires frequent changes of secrets at the various SNMP entities. to make this deployable in a large operational environment, these SNMP parameters need to be remotely configurable 📡
- Controlled Complexity it's recognized that producers of simple managed devices want to keep the resources used by SNMP to a minimum 🪶 at the same time, there's a need for more complex configurations that can spend more resources on SNMP and thus provide more functionality 🚀 the design tries to balance the competing requirements of these two environments, and it lets the more complex environments logically extend the simple one 💜
2. Documentation Overview ✨
okay so this is the map of every doc that fits into the SNMP Architecture 🗺️ bestie, here's the figure:
+------------------------- Document Set ----------------------------+
| |
| +------------+ +-----------------+ +----------------+ |
| | Document * | | Applicability * | | Coexistence * | |
| | Roadmap | | Statement | | & Transition | |
| +------------+ +-----------------+ +----------------+ |
| |
| +---------------------------------------------------------------+ |
| | Message Handling | |
| | +----------------+ +-----------------+ +-----------------+ | |
| | | Transport | | Message | | Security | | |
| | | Mappings | | Processing and | | | | |
| | | | | Dispatcher | | | | |
| | +----------------+ +-----------------+ +-----------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | PDU Handling | |
| | +----------------+ +-----------------+ +-----------------+ | |
| | | Protocol | | Applications | | Access | | |
| | | Operations | | | | Control | | |
| | +----------------+ +-----------------+ +-----------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | Information Model | |
| | +--------------+ +--------------+ +---------------+ | |
| | | Structure of | | Textual | | Conformance | | |
| | | Management | | Conventions | | Statements | | |
| | | Information | | | | | | |
| | +--------------+ +--------------+ +---------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | MIBs | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| | | Standard v1 | | Standard v1 | | Historic | | Draft v2 | | |
| | | RFC1157 | | RFC1212 | | RFC14XX | | RFC19XX | | |
| | | format | | format | | format | | format | | |
| | +-------------+ +-------------+ +----------+ +----------+ | |
| +---------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+Note: RFC14XX means RFCs 1442, 1443, and 1444. RFC19XX means RFCs 1902, 1903, and 1904.
Those marked with an asterisk (*) are expected to be written in the future 🔮 Each of these docs may be replaced or supplemented, no cap. This Architecture document specifically describes how new docs fit into the set of docs in the area of Message and PDU handling 🎀
2.1. Document Roadmap 🛣️
One or more docs may be written to describe how sets of docs taken together form specific Frameworks 💅 The configuration of doc sets might change over time, so the "road map" should be maintained in a doc separate from the standards docs themselves. Literally a whole different vibe 🙈
2.2. Applicability Statement 🧭
SNMP is used in networks that vary widely in size and complexity, by organizations that vary widely in their requirements of management. It's giving "one size does NOT fit all" 💖 Some models will be designed to address specific problems of management, such as message security.
One or more docs may be written to describe the environments to which certain versions of SNMP or models within SNMP would be appropriately applied, and those to which a given model might be inappropriately applied. Knowing where things don't belong is lowkey just as important 🫶
2.3. Coexistence and Transition 🦋
The purpose of an evolutionary architecture is to permit new models to replace or supplement existing models. The interactions between models could result in incompatibilities, security "holes", and other undesirable effects 😭
The purpose of Coexistence docs is to detail recognized anomalies and to describe required and recommended behaviors for resolving the interactions between models within the architecture. Coexistence docs may be prepared separately from model definition docs, to describe and resolve interaction anomalies between a model definition and one or more other model definitions. Main character energy for fixing the drama 👑
Additionally, recommendations for transitions between models may also be described, either in a coexistence doc or in a separate doc. ✨
2.4. Transport Mappings 🚚
SNMP messages are sent over various transports. It is the purpose of Transport Mapping docs to define how the mapping between SNMP and the transport is done. 🌸
2.5. Message Processing 📨
A Message Processing Model doc defines a message format, which is typically identified by a version field in an SNMP message header. The doc may also define a MIB module for use in message processing and for instrumentation of version-specific interactions 🧚
An SNMP engine includes one or more Message Processing Models, and thus may support sending and receiving multiple versions of SNMP messages. Versatile queen behavior 👸
2.6. Security 🔐
Some environments require secure protocol interactions. Security is normally applied at two different stages:
- in the transmission/receipt of messages, and
- in the processing of the contents of messages.
For purposes of this doc, "security" refers to message-level security; "access control" refers to the security applied to protocol operations. Two different bouncers, two different jobs 💅
Authentication, encryption, and timeliness checking are common functions of message level security 🔒
A security doc describes a Security Model, the threats against which the model protects, the goals of the Security Model, the protocols which it uses to meet those goals, and it may define a MIB module to describe the data used during processing, and to allow the remote configuration of message-level security parameters, such as passwords. Passwords are not for sharing, bestie 🙈
An SNMP engine may support multiple Security Models concurrently. 💜
2.7. Access Control 🚪
During processing, it may be required to control access to managed objects for operations.
An Access Control Model defines mechanisms to determine whether access to a managed object should be allowed. An Access Control Model may define a MIB module used during processing and to allow the remote configuration of access control policies. Who gets in, and who stays out 🍓
2.8. Protocol Operations 🧾
SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). It is the purpose of a Protocol Operations doc to define the operations of the protocol with respect to the processing of the PDUs. The PDU is the package, and this doc is the instruction manual 📦
An application doc defines which Protocol Operations docs are supported by the application. ✨
2.9. Applications 🎀
An SNMP entity normally includes a number of applications. Applications use the services of an SNMP engine to accomplish specific tasks. They coordinate the processing of management information operations, and may use SNMP messages to communicate with other SNMP entities. Teamwork makes the dream work 🫶
Applications docs describe the purpose of an application, the services required of the associated SNMP engine, and the protocol operations and informational model that the application uses to perform management operations.
An application doc defines which set of docs are used to specifically define the structure of management information, textual conventions, conformance requirements, and operations supported by the application. Every app has its own little rulebook 📖
2.10. Structure of Management Information 🏗️
Management information is viewed as a collection of managed objects, residing in a virtual information store, termed the Management Information Base (MIB). Collections of related objects are defined in MIB modules. Think of the MIB as a big organized binder 🗂️
It is the purpose of a Structure of Management Information doc to establish the syntax for defining objects, modules, and other elements of managed information. The grammar rules, basically 🧠
2.11. Textual Conventions 🔤
When designing a MIB module, it is often useful to define new types similar to those defined in the SMI, but with more precise semantics, or which have special semantics associated with them. These newly defined types are termed textual conventions, and may be defined in separate docs, or within a MIB module. Custom types with extra sparkle ✨
2.12. 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. Receipts for what you actually built 🧾💖
2.13. Management Information Base Modules 📚
MIB docs describe collections of managed objects which instrument some aspect of a managed node. Little instrumentation sets for every corner of the network 🌈
2.13.1. SNMP Instrumentation MIBs 🪞
An SNMP MIB doc may define a collection of managed objects which instrument the SNMP protocol itself. In addition, MIB modules may be defined within the docs which describe portions of the SNMP architecture, such as the docs for Message processing Models, Security Models, etc. for the purpose of instrumenting those Models, and for the purpose of allowing remote configuration of the Model. The protocol checking itself, iykyk 🙈
2.14. SNMP Framework Documents 🖼️
This architecture is designed to allow an orderly evolution of portions of SNMP Frameworks. Growth without chaos, periodt 🌱
Throughout the rest of this doc, the term "subsystem" refers to an abstract and incomplete specification of a portion of a Framework, that is further refined by a model specification.
A "model" describes a specific design of a subsystem, defining additional constraints and rules for conformance to the model. A model is sufficiently detailed to make it possible to implement the specification. Blueprint energy 📐
An "implementation" is an instantiation of a subsystem, conforming to one or more specific models. The finished outfit, bestie 👗
SNMP version 1 (SNMPv1), is the original Internet-standard Network Management Framework, as described in RFCs 1155, 1157, and 1212. The OG 🦖
SNMP version 2 (SNMPv2), is the SNMPv2 Framework as derived from the SNMPv1 Framework. It is described in RFCs 1902-1907. SNMPv2 has no message definition. Glow-up, but no new outfit 💅
The Community-based SNMP version 2 (SNMPv2c), is an experimental SNMP Framework which supplements the SNMPv2 Framework, as described in RFC1901. It adds the SNMPv2c message format, which is similar to the SNMPv1 message format. Experimental era, still iconic 🧪
SNMP version 3 (SNMPv3), is an extensible SNMP Framework which supplements the SNMPv2 Framework, by supporting the following:
- a new SNMP message format,
- Security for Messages, and
- Access Control.
Other SNMP Frameworks, i.e., other configurations of implemented subsystems, are expected to also be consistent with this architecture. Everyone's invited to the party 🎉
3. Elements of the Architecture ✨
okay so this section is the part where we meet all the pieces of the architecture and figure out what each one is called 🎀 there are three kinds of naming going on:
- the naming of entities,
- the naming of identities, and
- the naming of management information.
the architecture also gives names to a few other constructs that the documentation uses, so we're covering those too 🧚
3.1. The Naming of Entities 🌸
first things first, an SNMP entity is an implementation of this architecture 💖 every SNMP entity is made of an SNMP engine plus one or more associated applications. the figure below shows what's inside an entity bestie 👀
+-------------------------------------------------------------------+
| SNMP entity |
| |
| +-------------------------------------------------------------+ |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| | | | | | | | | | | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | | | | | | | | | | |
| | +------------+ +------------+ +-----------+ +-----------+ | |
| | | |
| +-------------------------------------------------------------+ |
| |
| +-------------------------------------------------------------+ |
| | Application(s) | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Proxy | | |
| | | Generator | | Receiver | | Forwarder | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | Command | | Notification | | Other | | |
| | | Responder | | Originator | | | | |
| | +-------------+ +--------------+ +--------------+ | |
| | | |
| +-------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+3.1.1. SNMP engine 🦋
the SNMP engine is the one that provides services for sending and receiving messages, authenticating and encrypting messages, and controlling access to managed objects 💅 there's a one-to-one association between an SNMP engine and the SNMP entity that contains it. the engine contains:
- a Dispatcher,
- a Message Processing Subsystem,
- a Security Subsystem, and
- an Access Control Subsystem.
3.1.1.1. snmpEngineID 🔑
okay this one is iconic 😭 within an administrative domain, an snmpEngineID is the unique and unambiguous identifier of an SNMP engine. since there's a one-to-one association between SNMP engines and SNMP entities, it also uniquely and unambiguously identifies the SNMP entity. main character energy for sure 👑
3.1.1.2. Dispatcher 💜
there is only one Dispatcher in an SNMP engine, no cap 🧚 it's what lets the engine handle multiple versions of SNMP messages at the same time ✨ it does this by:
- sending and receiving SNMP messages to/from the network,
- determining the version of an SNMP message and interacting with the corresponding Message Processing Model,
- providing an abstract interface to SNMP applications for delivery of a PDU to an application.
- providing an abstract interface for SNMP applications that allows them to send a PDU to a remote SNMP entity.
3.1.1.3. Message Processing Subsystem 🌈
the Message Processing Subsystem is responsible for preparing messages for sending, and for extracting data from received messages 🫶 it can hold multiple Message Processing Models, which look like this:
* One or more Message Processing Models may be present.
+------------------------------------------------------------------+
| |
| Message Processing Subsystem |
| |
| +------------+ +------------+ +------------+ +------------+ |
| | * | | * | | * | | * | |
| | SNMPv3 | | SNMPv1 | | SNMPv2c | | Other | |
| | Message | | Message | | Message | | Message | |
| | Processing | | Processing | | Processing | | Processing | |
| | Model | | Model | | Model | | Model | |
| | | | | | | | | |
| +------------+ +------------+ +------------+ +------------+ |
| |
+------------------------------------------------------------------+3.1.1.3.1. Message Processing Model 🎀
each Message Processing Model defines the format of one particular version of an SNMP message. it also coordinates preparing and extracting that version-specific message format 💖
3.1.1.4. Security Subsystem 🔐
the Security Subsystem provides security services like the authentication and privacy of messages, and it can hold multiple Security Models, as the figure shows 🛡️
* One or more Security Models may be present.
+------------------------------------------------------------------+
| |
| Security Subsystem |
| |
| +----------------+ +-----------------+ +-------------------+ |
| | * | | * | | * | |
| | User-Based | | Other | | Other | |
| | Security | | Security | | Security | |
| | Model | | Model | | Model | |
| | | | | | | |
| +----------------+ +-----------------+ +-------------------+ |
| |
+------------------------------------------------------------------+3.1.1.4.1. Security Model 🦄
a Security Model defines the threats it protects against, the goals of its services, and the security protocols it uses to provide services like authentication and privacy 😤
3.1.1.4.2. Security Protocol 🍓
a Security Protocol defines the mechanisms, procedures, and MIB data it uses to provide a security service like authentication or privacy ✨
3.1.2. Access Control Subsystem 👑
the Access Control Subsystem provides authorization services by means of one or more Access Control Models 💅
+------------------------------------------------------------------+
| |
| Access Control Subsystem |
| |
| +---------------+ +-----------------+ +------------------+ |
| | * | | * | | * | |
| | View-Based | | Other | | Other | |
| | Access | | Access | | Access | |
| | Control | | Control | | Control | |
| | Model | | Model | | Model | |
| | | | | | | |
| +---------------+ +-----------------+ +------------------+ |
| |
+------------------------------------------------------------------+3.1.2.1. Access Control Model 🌷
an Access Control Model defines a particular access decision function, which supports decisions about access rights 🔥
3.1.3. Applications 💖
there are several types of applications, including:
- command generators, which monitor and manipulate management data,
- command responders, which provide access to management data,
- notification originators, which initiate asynchronous messages,
- notification receivers, which process asynchronous messages, and
- proxy forwarders, which forward messages between entities.
these applications use the services the SNMP engine provides 🫶
3.1.3.1. SNMP Manager 👑
okay so an SNMP entity with one or more command generator and/or notification receiver applications (plus their associated SNMP engine) has traditionally been called an SNMP manager 💅 one or more models may be present, so it can be as busy as you want 🫶
(traditional SNMP manager)
+-------------------------------------------------------------------+
| +--------------+ +--------------+ +--------------+ SNMP entity |
| | NOTIFICATION | | NOTIFICATION | | COMMAND | |
| | ORIGINATOR | | RECEIVER | | GENERATOR | |
| | applications | | applications | | applications | |
| +--------------+ +--------------+ +--------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------+--------+-----------------+ |
| ^ |
| | +---------------------+ +----------------+ |
| | | Message Processing | | Security | |
| Dispatcher v | Subsystem | | Subsystem | |
| +-------------------+ | +------------+ | | | |
| | PDU Dispatcher | | +->| v1MP * |<--->| +------------+ | |
| | | | | +------------+ | | | Other | | |
| | | | | +------------+ | | | Security | | |
| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->+ | | | |
| | | | | +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | User-based | | |
| | Transport | | | +------------+ | | | Security | | |
| | Mapping | | | +------------+ | | | Model | | |
| | (e.g RFC1906) | | +->| otherMP * |<--->| +------------+ | |
| +-------------------+ | +------------+ | | | |
| ^ +---------------------+ +----------------+ |
| | |
| v |
+-------------------------------------------------------------------+
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | |
v v v
+------------------------------+
| Network |
+------------------------------+3.1.3.2. SNMP Agent ✨
the flip side! an SNMP entity with one or more command responder and/or notification originator applications (plus their associated SNMP engine) has traditionally been called an SNMP agent 🦋
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+
| ^ |
| | +---------------------+ +----------------+ |
| | | Message Processing | | Security | |
| Dispatcher v | Subsystem | | Subsystem | |
| +-------------------+ | +------------+ | | | |
| | Transport | | +->| v1MP * |<--->| +------------+ | |
| | Mapping | | | +------------+ | | | Other | | |
| | (e.g. RFC1906) | | | +------------+ | | | Security | | |
| | | | +->| v2cMP * |<--->| | Model | | |
| | Message | | | +------------+ | | +------------+ | |
| | Dispatcher <--------->| +------------+ | | +------------+ | |
| | | | +->| v3MP * |<--->| | User-based | | |
| | | | | +------------+ | | | Security | | |
| | PDU Dispatcher | | | +------------+ | | | Model | | |
| +-------------------+ | +->| otherMP * |<--->| +------------+ | |
| ^ | +------------+ | | | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY * | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+3.2. The Naming of Identities 🎀
here's how identities get their names, bestie 🧚
principal
^
|
|
+----------------------------|-------------+
| SNMP engine v |
| +--------------+ |
| | | |
| +-----------------| securityName |---+ |
| | Security Model | | | |
| | +--------------+ | |
| | ^ | |
| | | | |
| | v | |
| | +------------------------------+ | |
| | | | | |
| | | Model | | |
| | | Dependent | | |
| | | Security ID | | |
| | | | | |
| | +------------------------------+ | |
| | ^ | |
| | | | |
| +-------------------------|----------+ |
| | |
| | |
+----------------------------|-------------+
|
v
network3.2.1. Principal 💜
a principal is the "who" that services are provided for, or that processing happens on behalf of 🙈
a principal can be a bunch of different things, like one individual playing a specific role, a group of individuals each playing a role, an application or a set of applications, or any mix of those 🌈
3.2.2. securityName 🍓
a securityName is a human readable string that represents a principal ✨ it has a format that doesn't depend on the model, so it can be used outside of any particular Security Model 🫶
3.2.3. Model-dependent security ID 🦋
a model-dependent security ID is the model-specific version of a securityName inside a particular Security Model 💅
these IDs may or may not be human readable, and their syntax depends on the model ngl 😭 examples include community names, user names, and parties
turning model-dependent security IDs into securityNames (and back again) is the job of the relevant Security Model 👑
3.3. The Naming of Management Information 🌸
management information lives at an SNMP entity where a Command Responder Application has local access to potentially multiple contexts 🔥 this application uses a contextEngineID that's equal to the snmpEngineID of its associated SNMP engine
+-----------------------------------------------------------------+
| SNMP entity (identified by snmpEngineID, example: abcd) |
| |
| +------------------------------------------------------------+ |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | | | | | | | | | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | | | | | | | | | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | Command Responder Application | |
| | (contextEngineID, example: abcd) | |
| | | |
| | example contextNames: | |
| | | |
| | "bridge1" "bridge2" "" (default) | |
| | --------- --------- ------------ | |
| | | | | | |
| +------|------------------|-------------------|--------------+ |
| | | | |
| +------|------------------|-------------------|--------------+ |
| | MIB | instrumentation | | | |
| | +---v------------+ +---v------------+ +----v-----------+ | |
| | | context | | context | | context | | |
| | | | | | | | | |
| | | +------------+ | | +------------+ | | +------------+ | | |
| | | | bridge MIB | | | | bridge MIB | | | | other MIB | | | |
| | | +------------+ | | +------------+ | | +------------+ | | |
| | | | | | | | | |
| | | | | | | +------------+ | | |
| | | | | | | | some MIB | | | |
| | | | | | | +------------+ | | |
| | | | | | | | | |
+-----------------------------------------------------------------+3.3.1. An SNMP Context ✨
okay so an SNMP context (or just "context" for short 💅) is a collection of management information that an SNMP entity can access. The same item of management info can live in more than one context, and an SNMP entity can have access to lots of contexts at once 🫶
here's the thing: there are usually tons of instances of each managed object type in a management domain 😭 so the MIB module's way of identifying instances doesn't let each one be told apart from every other instance in the whole domain. instead, each instance only needs to be identified within some scope (aka a "context"), and the management domain has multiple contexts. 🦋
a context is often a physical device, or maybe a logical one, but it can also cover several devices, a piece of a single device, or even pieces of several devices. the one rule is that a context is always defined as a subset of a single SNMP entity 👑 so to pin down one specific item of management info in the domain, you need its contextName and contextEngineID on top of its object type and instance.
for example, the managed object type ifDescr [RFC1573] is the description of a network interface. to find the description of device-X's first network interface, you need four things: the snmpEngineID of the SNMP entity that gives access to the management info at device-X, the contextName (device-X), the managed object type (ifDescr), and the instance ("1") 🤩
every context has (at least) one unique identification within the management domain. the same item of management info can exist in multiple contexts, and it can also have multiple unique identifications. that happens when the item shows up in multiple contexts, and it also happens when a context has multiple unique identifications 🌈
the combination of a contextEngineID and a contextName unambiguously identifies a context within an administrative domain. just note that there can be multiple unique combinations of contextEngineID and contextName that unambiguously identify the same context 💜
3.3.2. contextEngineID
within an administrative domain, a contextEngineID uniquely identifies an SNMP entity that may realize an instance of a context with a particular contextName 🧚
3.3.3. contextName
a contextName is used to name a context. Each contextName MUST be unique within an SNMP entity. no exceptions, bestie 🚨
3.3.4. scopedPDU
a scopedPDU is a block of data containing a contextEngineID, a contextName, and a PDU 🎀
the PDU is an SNMP Protocol Data Unit holding info that's named in the context. that info is unambiguously identified within an administrative domain by the combo of the contextEngineID and the contextName. see, for example, RFC1905 for more deets on SNMP PDUs 📖
3.4. Other Constructs 🍓
3.4.1. maxSizeResponseScopedPDU
the maxSizeResponseScopedPDU is the maximum size of a scopedPDU that's allowed to be included in a response message. side note: the size of a scopedPDU does not include the size of the SNMP message header 🙈
3.4.2. Local Configuration Datastore
the subsystems, models, and applications inside an SNMP entity may need to keep their own sets of configuration info 🗂️
some of that config info might be accessible as managed objects too ✨
the whole collection of these sets of info is called an entity's Local Configuration Datastore (LCD) 💖
3.4.3. securityLevel
this architecture recognizes three levels of security, and they're giving main character energy 👑
- without authentication and without privacy (
noAuthNoPriv) - with authentication but without privacy (
authNoPriv) - with authentication and with privacy (
authPriv)
these three values are ordered, so noAuthNoPriv is less than authNoPriv, and authNoPriv is less than authPriv 📊
every message has an associated securityLevel. all Subsystems (Message Processing, Security, Access Control) and applications are required to either supply a value of securityLevel or abide by the supplied value of securityLevel while processing the message and its contents 🔒
4. Abstract Service Interfaces 🧩
abstract service interfaces are defined to describe the conceptual interfaces between the various subsystems inside an SNMP entity 🦋
these interfaces are defined by a set of primitives. the primitives describe the services provided and the abstract data elements that get passed when the services are invoked. this section lists the primitives defined for the various subsystems 💅
4.1. Dispatcher Primitives
the Dispatcher typically provides services to the SNMP applications through its PDU Dispatcher. this section describes the primitives the PDU Dispatcher provides ✨
4.1.1. Generate Outgoing Request or Notification
the PDU Dispatcher provides the following primitive for an application to send an SNMP Request or Notification to another SNMP entity 📤
statusInformation = -- sendPduHandle if success
-- errorIndication if failure
sendPdu(
IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
)4.1.2. Process Incoming Request or Notification PDU
the PDU Dispatcher provides the following primitive to pass an incoming SNMP PDU to an application 📥
processPdu( -- process Request/Notification PDU
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
) -- needed when sending a response4.1.3. Generate Outgoing Response
the PDU Dispatcher provides the following primitive for an application to hand an SNMP Response PDU back to the PDU Dispatcher 🔁
returnResponsePdu(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
-- as presented with the request
IN statusInformation -- success or errorIndication
) -- error counter OID/value if error4.1.4. Process Incoming Response PDU
the PDU Dispatcher provides the following primitive to pass an incoming SNMP Response PDU to an application 📬
processResponsePdu( -- process Response PDU
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN statusInformation -- success or errorIndication
IN sendPduHandle -- handle from sendPdu
)4.1.5. Registering Responsibility for Handling SNMP PDUs
applications can register or unregister responsibility for a specific contextEngineID, for specific pduTypes, with the PDU Dispatcher using the primitives below. which particular pduTypes an application can register for is decided by the Message Processing Model(s) supported by the SNMP entity that holds the PDU Dispatcher 🗝️
statusInformation = -- success or errorIndication
registerContextEngineID(
IN contextEngineID -- take responsibility for this one
IN pduType -- the pduType(s) to be registered
)
unregisterContextEngineID(
IN contextEngineID -- give up responsibility for this one
IN pduType -- the pduType(s) to be unregistered
)note that realizations of the registerContextEngineID and unregisterContextEngineID abstract service interfaces may provide implementation-specific ways for applications to register or deregister responsiblity for all possible values of the contextEngineID or pduType parameters 🌸
4.2. Message Processing Subsystem Primitives
the Dispatcher works with a Message Processing Model to process a specific version of an SNMP Message. this section describes the primitives the Message Processing Subsystem provides 📦
4.2.1. Prepare Outgoing SNMP Request or Notification Message
the Message Processing Subsystem provides this service primitive for preparing an outgoing SNMP Request or Notification Message 🛠️
statusInformation = -- success or errorIndication
prepareOutgoingMessage(
IN transportDomain -- transport domain to be used
IN transportAddress -- transport address to be used
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- the handle for matching
-- incoming responses
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length
)4.2.2. Prepare an Outgoing SNMP Response Message ✨
Okay bestie, this one is the Message Processing Subsystem's move for cooking up an outgoing SNMP Response Message 🎀. Here's the primitive:
result = -- SUCCESS or FAILURE
prepareResponseMessage(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- same as on incoming request
IN securityName -- same as on incoming request
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of the Response PDU
IN stateReference -- reference to state information
-- as presented with the request
IN statusInformation -- success or errorIndication
-- error counter OID/value if error
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length
)4.2.3. Prepare Data Elements from an Incoming SNMP Message 📦
Next up is the primitive that unpacks an incoming SNMP message into its abstract data elements 🧚. Same Message Processing Subsystem, different vibe.
result = -- SUCCESS or errorIndication
prepareDataElements(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN wholeMsg -- as received from the network
IN wholeMsgLength -- as received from the network
OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use
OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context
OUT pduVersion -- the version of the PDU
OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for matched request
OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU
OUT statusInformation -- success or errorIndication
-- error counter OID/value if error
OUT stateReference -- reference to state information
-- to be used for possible Response
)4.3. Access Control Subsystem Primitives 🔐
Applications are the usual clients of the Access Control Subsystem's services 💅.
The Access Control Subsystem gives you one primitive to check whether access is allowed 👑:
statusInformation = -- success or errorIndication
isAccessAllowed(
IN securityModel -- Security Model in use
IN securityName -- principal who wants to access
IN securityLevel -- Level of Security
IN viewType -- read, write, or notify view
IN contextName -- context containing variableName
IN variableName -- OID for the managed object
)4.4. Security Subsystem Primitives 🔒
The Message Processing Subsystem is the one that usually calls on the Security Subsystem 🫶.
4.4.1. Generate a Request or Notification Message 📨
The Security Subsystem offers this primitive for building a Request or Notification message 💜:
statusInformation =
generateRequestMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)4.4.2. Process Incoming Message 📬
For handling an incoming message, the Security Subsystem gives you this primitive 🔍:
statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
OUT securityEngineID -- identification of the principal
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size of the Response PDU
OUT securityStateReference -- reference to security state
) -- information, needed for response4.4.3. Generate a Response Message 📤
When it's time to reply, the Security Subsystem uses this primitive to generate a Response message 🌸:
statusInformation =
generateResponseMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- for the outgoing message
IN scopedPDU -- message (plaintext) payload
IN securityStateReference -- reference to security state
-- information from original request
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)4.5. Common Primitives 🧩
These primitives are shared by more than one Subsystem 🌈.
4.5.1. Release State Reference Information 🗑️
Any Subsystem that passes stateReference information around also has to provide a primitive that frees the memory holding that state information ✨:
stateRelease(
IN stateReference -- handle of reference to be released
)4.6. Scenario Diagrams 🎬
4.6.1. Command Generator or Notification Originator 🦋
This diagram walks through how a Command Generator or Notification Originator application asks for a PDU to be sent, and how the response comes back to that application (asynchronously) 💖.
Command Dispatcher Message Security
Generator | Processing Model
| | Model |
| sendPdu | | |
|------------------->| | |
| | prepareOutgoingMessage | |
: |----------------------->| |
: | | generateRequestMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
: | | |
: |------------------+ | |
: | Send SNMP | | |
: | Request Message | | |
: | to Network | | |
: | v | |
: : : : :
: : : : :
: : : : :
: | | | |
: | Receive SNMP | | |
: | Response Message | | |
: | from Network | | |
: |<-----------------+ | |
: | | |
: | prepareDataElements | |
: |----------------------->| |
: | | processIncomingMsg |
: | |-------------------->|
: | | |
: | |<--------------------|
: | | |
: |<-----------------------| |
| processResponsePdu | | |
|<-------------------| | |
| | | |4.6.2. Scenario Diagram for a Command Responder Application ✨
okay so this diagram is giving main character energy 💅. It shows how a Command Responder or Notification Receiver app signs up for handling a pduType 🎀, how a PDU gets dispatched to that app once an SNMP message comes in 📨, and how the Response gets sent back to the network (asynchronously, bestie) 🦋.
Command Dispatcher Message Security
Responder | Processing Model
| | Model |
| | | |
| registerContextEngineID | | |
|------------------------>| | |
|<------------------------| | | |
| | Receive SNMP | | |
: | Message | | |
: | from Network | | |
: |<-------------+ | |
: | | |
: |prepareDataElements | |
: |------------------->| |
: | | processIncomingMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
| processPdu | | |
|<------------------------| | |
| | | |
: : : :
: : : :
| returnResponsePdu | | |
|------------------------>| | |
: | prepareResponseMsg | |
: |------------------->| |
: | |generateResponseMsg |
: | |------------------->|
: | | |
: | |<-------------------|
: | | |
: |<-------------------| |
: | | |
: |--------------+ | |
: | Send SNMP | | |
: | Message | | |
: | to Network | | |
: | v | |5. Managed Object Definitions for SNMP Management Frameworks ✨
okay now the good stuff 🧚. This is the SNMP-FRAMEWORK-MIB module, the MIB that defines the managed objects for the SNMP Management Architecture. It's literally where the textual conventions live, so the shapes of things like engine IDs and security model values are spelled out here 💜.
SNMP-FRAMEWORK-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY,
snmpModules FROM SNMPv2-SMI
TEXTUAL-CONVENTION FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF;
snmpFrameworkMIB MODULE-IDENTITY
LAST-UPDATED "9711200000Z" -- 20 November 1997
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: snmpv3@tis.com
Subscribe: majordomo@tis.com
In message body: subscribe snmpv3
Chair: Russ Mundy
Trusted Information Systems
postal: 3060 Washington Rd
Glenwood MD 21738
USA
email: mundy@tis.com
phone: +1 301-854-6889
Co-editor Dave Harrington
Cabletron Systems, Inc.
postal: Post Office Box 5005
Mail Stop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA
email: dbh@ctron.com
phone: +1 603-337-7357
Co-editor Randy Presuhn
BMC Software, Inc.
postal: 1190 Saratoga Avenue
Suite 130
San Jose, CA 95129
USA
email: rpresuhn@bmc.com
phone: +1 408-556-0720
Co-editor: Bert Wijnen
IBM T.J. Watson Research
postal: Schagen 33
3461 GL Linschoten
Netherlands
email: wijnen@vnet.ibm.com
phone: +31 348-432-794
"
DESCRIPTION "The SNMP Management Architecture MIB"
::= { snmpModules 10 }
-- Textual Conventions used in the SNMP Management Architecture ***
SnmpEngineID ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
The value for this object may not be all zeros or
all 'ff'H or the empty (zero length) string.
The initial value for this object may be configured
via an operator console entry or via an algorithmic
function. In the latter case, the following
example algorithm is recommended.
In cases where there are multiple engines on the
same system, the use of this algorithm is NOT
appropriate, as it would result in all of those
engines ending up with the same ID value.
1) The very first bit is used to indicate how the
rest of the data is composed.
0 - as defined by enterprise using former methods
that existed before SNMPv3. See item 2 below.
1 - as defined by this architecture, see item 3
below.
Note that this allows existing uses of the
engineID (also known as AgentID [RFC1910]) to
co-exist with any new uses.
2) The snmpEngineID has a length of 12 octets.
The first four octets are set to the binary
equivalent of the agent's SNMP management
private enterprise number as assigned by the
Internet Assigned Numbers Authority (IANA).
For example, if Acme Networks has been assigned
{ enterprises 696 }, the first four octets would
be assigned '000002b8'H.
The remaining eight octets are determined via
one or more enterprise-specific methods. Such
methods must be designed so as to maximize the
possibility that the value of this object will
be unique in the agent's administrative domain.
For example, it may be the IP address of the SNMP
entity, or the MAC address of one of the
interfaces, with each address suitably padded
with random octets. If multiple methods are
defined, then it is recommended that the first
octet indicate the method being used and the
remaining octets be a function of the method.
3) The length of the octet strings varies.
The first four octets are set to the binary
equivalent of the agent's SNMP management
private enterprise number as assigned by the
Internet Assigned Numbers Authority (IANA).
For example, if Acme Networks has been assigned
{ enterprises 696 }, the first four octets would
be assigned '000002b8'H.
The very first bit is set to 1. For example, the
above value for Acme Networks now changes to be
'800002b8'H.
The fifth octet indicates how the rest (6th and
following octets) are formatted. The values for
the fifth octet are:
0 - reserved, unused.
1 - IPv4 address (4 octets)
lowest non-special IP address
2 - IPv6 address (16 octets)
lowest non-special IP address
3 - MAC address (6 octets)
lowest IEEE MAC address, canonical
order
4 - Text, administratively assigned
Maximum remaining length 27
5 - Octets, administratively assigned
Maximum remaining length 27
6-127 - reserved, unused
127-255 - as defined by the enterprise
Maximum remaining length 27
"
SYNTAX OCTET STRING (SIZE(1..32))
SnmpSecurityModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a
securityModel of the Security Subsystem within the
SNMP Management Architecture.
The values for securityModel are allocated as
follows:
- The zero value is reserved.
- Values between 1 and 255, inclusive, are reserved
for standards-track Security Models and are
managed by the Internet Assigned Numbers Authority
(IANA).
- Values greater than 255 are allocated to
enterprise-specific Security Models. An
enterprise-specific securityModel value is defined
to be:
enterpriseID * 256 + security model within
enterprise
For example, the fourth Security Model defined by
the enterprise whose enterpriseID is 1 would be
260.
This scheme for allocation of securityModel
values allows for a maximum of 255 standards-
based Security Models, and for a maximum of
255 Security Models per enterprise.Okay bestie, we're still inside the SnmpSecurityModel textual convention, so let's pick up right where it left off 💖
It is believed that the assignment of new
securityModel values will be rare in practice
because the larger the number of simultaneously
utilized Security Models, the larger the
chance that interoperability will suffer.
Consequently, it is believed that such a range
will be sufficient. In the unlikely event that
the standards committee finds this number to be
insufficient over time, an enterprise number
can be allocated to obtain an additional 255
possible values.
Note that the most significant bit must be zero;
hence, there are 23 bits allocated for various
organizations to design and define non-standard
securityModels. This limits the ability to
define new proprietary implementations of Security
Models to the first 8,388,608 enterprises.
It is worthwhile to note that, in its encoded
form, the securityModel value will normally
require only a single byte since, in practice,
the leftmost bits will be zero for most messages
and sign extension is suppressed by the encoding
rules.
As of this writing, there are several values
of securityModel defined for use with SNMP or
reserved for use with supporting MIB objects.
They are as follows:
0 reserved for 'any'
1 reserved for SNMPv1
2 reserved for SNMPv2c
3 User-Based Security Model (USM)
"
SYNTAX INTEGER(0..2147483647)
SnmpMessageProcessingModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a Message
Processing Model of the Message Processing
Subsystem within a SNMP Management Architecture.
The values for messageProcessingModel are
allocated as follows:
- Values between 0 and 255, inclusive, are
reserved for standards-track Message Processing
Models and are managed by the Internet Assigned
Numbers Authority (IANA).
- Values greater than 255 are allocated to
enterprise-specific Message Processing Models.
An enterprise messageProcessingModel value is
defined to be:
enterpriseID * 256 +
messageProcessingModel within enterprise
For example, the fourth Message Processing Model
defined by the enterprise whose enterpriseID
is 1 would be 260.
This scheme for allocation of securityModel
values allows for a maximum of 255 standards-
based Message Processing Models, and for a
maximum of 255 Message Processing Models per
enterprise.
It is believed that the assignment of new
messageProcessingModel values will be rare
in practice because the larger the number of
simultaneously utilized Message Processing Models,
the larger the chance that interoperability
will suffer. It is believed that such a range
will be sufficient. In the unlikely event that
the standards committee finds this number to be
insufficient over time, an enterprise number
can be allocated to obtain an additional 256
possible values.
Note that the most significant bit must be zero;
hence, there are 23 bits allocated for various
organizations to design and define non-standard
messageProcessingModels. This limits the ability
to define new proprietary implementations of
Message Processing Models to the first 8,388,608
enterprises.
It is worthwhile to note that, in its encoded
form, the securityModel value will normally
require only a single byte since, in practice,
the leftmost bits will be zero for most messages
and sign extension is suppressed by the encoding
rules.
As of this writing, there are several values of
messageProcessingModel defined for use with SNMP.
They are as follows:
0 reserved for SNMPv1
1 reserved for SNMPv2c
2 reserved for SNMPv2u and SNMPv2*
3 reserved for SNMPv3
"
SYNTAX INTEGER(0..2147483647)
SnmpSecurityLevel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "A Level of Security at which SNMP messages can be
sent or with which operations are being processed;
in particular, one of:
noAuthNoPriv - without authentication and
without privacy,
authNoPriv - with authentication but
without privacy,
authPriv - with authentication and
with privacy.
These three values are ordered such that
noAuthNoPriv is less than authNoPriv and
authNoPriv is less than authPriv.
"
SYNTAX INTEGER { noAuthNoPriv(1),
authNoPriv(2),
authPriv(3)
}
SnmpAdminString ::= TEXTUAL-CONVENTION
DISPLAY-HINT "255a"
STATUS current
DESCRIPTION "An octet string containing administrative
information, preferably in human-readable form.
To facilitate internationalization, this
information is represented using the ISO/IEC
IS 10646-1 character set, encoded as an octet
string using the UTF-8 transformation format
described in [RFC2044].
Since additional code points are added by
amendments to the 10646 standard from time
to time, implementations must be prepared to
encounter any code point from 0x00000000 to
0x7fffffff.
The use of control codes should be avoided.
When it is necessary to represent a newline,
the control code sequence CR LF should be used.
The use of leading or trailing white space should
be avoided.
For code points not directly supported by user
interface hardware or software, an alternative
means of entry and display, such as hexadecimal,
may be provided.
For information encoded in 7-bit US-ASCII,
the UTF-8 encoding is identical to the
US-ASCII encoding.
Note that when this TC is used for an object that
is used or envisioned to be used as an index, then
a SIZE restriction must be specified so that the
number of sub-identifiers for any object instance
does not exceed the limit of 128, as defined by
[RFC1905].
"
SYNTAX OCTET STRING (SIZE (0..255))Now the admin assignments section, where the object identifiers get their homes 🧚
-- Administrative assignments ***************************************
snmpFrameworkAdmin
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 }
snmpFrameworkMIBObjects
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 }
snmpFrameworkMIBConformance
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 }
-- the snmpEngine Group ********************************************
snmpEngine OBJECT IDENTIFIER ::= { snmpFrameworkMIBObjects 1 }
snmpEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-only
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
"
::= { snmpEngine 1 }
snmpEngineBoots OBJECT-TYPE
SYNTAX INTEGER (1..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of times that the SNMP engine has
(re-)initialized itself since its initial
configuration.
"
::= { snmpEngine 2 }
snmpEngineTime OBJECT-TYPE
SYNTAX INTEGER (0..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of seconds since the SNMP engine last
incremented the snmpEngineBoots object.
"
::= { snmpEngine 3 }
snmpEngineMaxMessageSize OBJECT-TYPE
SYNTAX INTEGER (484..2147483647)
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The maximum length in octets of an SNMP message
which this SNMP engine can send or receive and
process, determined as the minimum of the maximum
message size values supported among all of the
transports available to and supported by the engine.
"
::= { snmpEngine 4 }Next up are the registration points for the auth and privacy protocols, plus the conformance bits 🦋
-- Registration Points for Authentication and Privacy Protocols **
snmpAuthProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track
authentication protocols used in SNMP Management
Frameworks.
"
::= { snmpFrameworkAdmin 1 }
snmpPrivProtocols OBJECT-IDENTITY
STATUS current
DESCRIPTION "Registration point for standards-track privacy
protocols used in SNMP Management Frameworks.
"
::= { snmpFrameworkAdmin 2 }
-- Conformance information ******************************************
snmpFrameworkMIBCompliances
OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 1}
snmpFrameworkMIBGroups
OBJECT IDENTIFIER ::= {snmpFrameworkMIBConformance 2}
-- compliance statements
snmpFrameworkMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP engines which
implement the SNMP Management Framework MIB.
"
MODULE -- this module
MANDATORY-GROUPS { snmpEngineGroup }
::= { snmpFrameworkMIBCompliances 1 }
-- units of conformance
snmpEngineGroup OBJECT-GROUP
OBJECTS {
snmpEngineID,
snmpEngineBoots,
snmpEngineTime,
snmpEngineMaxMessageSize
}
STATUS current
DESCRIPTION "A collection of objects for identifying and
determining the configuration and current timeliness
values of an SNMP engine.
"
::= { snmpFrameworkMIBGroups 1 }
END6. Intellectual Property 💅
Okay so the IETF is not taking a side on whether any intellectual property or other rights someone claims over this tech are valid or how far they reach 🙈. It also doesn't say it went looking for any of them. If you want the IETF's rules on rights for standards-track and standards-related docs, check out BCP-11 📚. Copies of rights claims, promised licenses, or results from trying to get a general license for implementers or users can be requested from the IETF Secretariat 🎀.
The IETF also invites anyone to flag copyrights, patents, patent applications, or other proprietary rights that might cover tech needed to implement this standard ✨. Send that info to the IETF Executive Director, bestie 🫶.
7. Acknowledgements 🌸
This doc is the work of the SNMPv3 Working Group, and they deserve a huge round of applause 👏 Special shoutouts go to these WG members:
- Dave Battle (SNMP Research, Inc.)
- Uri Blumenthal (IBM T.J. Watson Research Center)
- Jeff Case (SNMP Research, Inc.)
- John Curran (BBN)
- T. Max Devlin (Hi-TECH Connections)
- John Flick (Hewlett Packard)
- David Harrington (Cabletron Systems Inc.)
- N.C. Hien (IBM T.J. Watson Research Center)
- Dave Levi (SNMP Research, Inc.)
- Louis A Mamakos (UUNET Technologies Inc.)
- Paul Meyer (Secure Computing Corporation)
- Keith McCloghrie (Cisco Systems)
- Russ Mundy (Trusted Information Systems, Inc.)
- Bob Natale (ACE*COMM Corporation)
- Mike O'Dell (UUNET Technologies Inc.)
- Dave Perkins (DeskTalk)
- Peter Polkinghorne (Brunel University)
- Randy Presuhn (BMC Software, Inc.)
- David Reid (SNMP Research, Inc.)
- Shawn Routhier (Epilogue)
- Juergen Schoenwaelder (TU Braunschweig)
- Bob Stewart (Cisco Systems)
- Bert Wijnen (IBM T.J. Watson Research Center)
The design is based on recommendations from the IETF Security and Administrative Framework Evolution for SNMP Advisory Team 🧚 Those people were:
- David Harrington (Cabletron Systems Inc.)
- Jeff Johnson (Cisco Systems)
- David Levi (SNMP Research Inc.)
- John Linn (Openvision)
- Russ Mundy (Trusted Information Systems) chair
- Shawn Routhier (Epilogue)
- Glenn Waters (Nortel)
- Bert Wijnen (IBM T. J. Watson Research Center)
The Advisory Team and the SNMPv3 Working Group Charter asked the design to borrow as much as practical from previous RFCs and drafts 📖 That's why special thanks go to the authors of the earlier designs known as SNMPv2u and SNMPv2* 🦋:
- Jeff Case (SNMP Research, Inc.)
- David Harrington (Cabletron Systems Inc.)
- David Levi (SNMP Research, Inc.)
- Keith McCloghrie (Cisco Systems)
- Brian O'Keefe (Hewlett Packard)
- Marshall T. Rose (Dover Beach Consulting)
- Jon Saperia (BGS Systems Inc.)
- Steve Waldbusser (International Network Services)
- Glenn W. Waters (Bell-Northern Research Ltd.)
8. Security Considerations 💀
Okay bestie, this section is SERIOUS 😭 Read every line.
This doc describes how an implementation can include a Security Model to protect management messages, plus an Access Control Model to control access to management info 🔐
How secure things are depends on which Security Model and which Access Control Model implementations you actually use 🛡️
Applications can reach data that is not secured. Applications should take reasonable steps to protect that data from disclosure 🙈
It's the purchaser's job to make sure that:
- an implementation follows the rules this architecture defines,
- the Security and Access Control Models they use meet their organization's security and access control needs,
- the implementations of the Models and Applications follow the model and application specs,
- and the implementation protects configuration secrets from accidental disclosure 🫣
9. References 📚
These are all the refs, with every detail kept:
- [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., Fedor, M., Schoffstall, M. and J. Davin, "The Simple Network Management Protocol", STD 15, RFC 1157, May 1990.
- [RFC1212] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16, RFC 1212, March 1991.
- [RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996.
- [RFC1902] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1902, January 1996.
- [RFC1905] 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] 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] 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] 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", RFC 1909, February 1996.
- [RFC1910] Waters, G., Editor, "User-based Security Model for SNMPv2", RFC 1910, February 1996.
- [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996.
- [RFC2044] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO 10646", RFC 2044, October 1996.
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
- [RFC2272] Case, J., Harrington, D., Presuhn, R., and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", RFC 2272, January 1998.
- [RFC2274] Blumenthal, U., and B. Wijnen, "The User-Based Security Model for Version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 2274, January 1998.
- [RFC2275] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access Control Model for the Simple Network Management Protocol (SNMP)", RFC 2275, January 1998.
- [RFC2273] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications", RFC 2273, January 1998.
10. Editors' Addresses 🎀
Here are the editors' contact details, copied exactly so you can reach them 💌
Bert Wijnen
IBM T.J. Watson Research
Schagen 33
3461 GL Linschoten
Netherlands
Phone: +31 348-432-794
EMail: wijnen@vnet.ibm.comDave Harrington
Cabletron Systems, Inc
Post Office Box 5005
Mail Stop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA
Phone: +1 603-337-7357
EMail: dbh@ctron.comRandy Presuhn
BMC Software, Inc.
1190 Saratoga Avenue
Suite 130
San Jose, CA 95129
USA
Phone: +1 408-556-0720
EMail: rpresuhn@bmc.comA. Guidelines for Model Designers 🧚
APPENDIX A 🌈
This appendix gives guidelines for designers of models that are supposed to fit into the architecture defined in this doc ✨
SNMPv1 and SNMPv2c are two SNMP frameworks that use communities for trivial authentication and access control 🍓 SNMPv1 and SNMPv2c Frameworks can coexist with Frameworks designed according to this architecture. Modified versions of them could be designed to meet this architecture's requirements, but this doc does not give 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 🚫
Data moving between subsystems is deliberately described as a fixed set of abstract data elements and primitive functions. Those can be overloaded to meet the needs of multiple model definitions 💜
Documents that define models for this architecture SHOULD use the standard primitives between subsystems, and they MAY define specific mechanisms for turning the abstract data elements into formats the model can use. This rule exists so subsystem and model docs can be written around the shared borders of the subsystem and model. Vendors don't have to respect those borders in their own implementations 🫶
The architecture defines certain standard services to be provided between subsystems, and it defines abstract service interfaces to request those services 🦋
Each model definition for a subsystem SHOULD support the standard service interfaces. Whether it does, how it does, or how well it does is up to the model definition 🌸
A.1. Security Model Design Requirements 🔐
A.1.1. Threats 💅
A document describing a Security Model MUST describe how the model protects against the threats described under "Security Requirements of this Architecture", section 1.4. ⭐
A.1.2. Security Processing 🔐✨
Okay bestie, every received message MUST be validated by a Model of the Security Subsystem 🛡️. That validation includes authentication and privacy processing if it's needed, but it's explicitly allowed to send messages that don't need authentication or privacy 💅.
A received message carries a specified securityLevel that gets used during processing. Any message that requires privacy MUST also require authentication 🔒, no exceptions, periodt.
A Security Model spells out the rules for how authentication and privacy get done 🧁. A model can add extra security features too, but its definition is constrained to using (possibly a subset of) the abstract data elements defined in this document for passing data between subsystems 🎀.
Each Security Model can allow multiple security protocols to run concurrently inside one implementation of the model 🌈. Each Security Model defines how to pick which protocol to use, based on the securityLevel and the security parameters relevant to the message. Each Security Model, together with its associated protocol(s), defines how the sending and receiving entities get identified, and how secrets get configured 🗝️.
Authentication and Privacy protocols supported by Security Models are uniquely identified using Object Identifiers 🆔. IETF standard protocols for authentication or privacy should have an identifier defined within the snmpAuthProtocols or the snmpPrivProtocols subtrees. Enterprise specific protocol identifiers should be defined within the enterprise subtree.
For privacy, the Security Model defines what portion of the message is encrypted 🙈.
The persistent data used for security should be SNMP-manageable, but the Security Model defines whether an instantiation of the MIB is a conformance requirement 📋.
Security Models are replaceable within the Security Subsystem 🔄. Multiple Security Model implementations may exist concurrently within an SNMP engine. The number of Security Models defined by the SNMP community should remain small to promote interoperability 🫶.
A.1.3. Validate the security-stamp in a received message ✅
A Message Processing Model requests that a Security Model:
- verifies that the message has not been altered,
- authenticates the identification of the principal for whom the message was generated.
- decrypts the message if it was encrypted.
Additional requirements may be defined by the model, and additional services may be provided by the model, but the model is constrained to use the following primitives for transferring data between subsystems. Implementations are not so constrained 🧩.
A Message Processing Model uses the processMsg primitive as described in section 4.5 🚀.
A.1.4. Security MIBs 📚
Each Security Model defines the MIB module(s) required for security processing, including any MIB module(s) required for the security protocol(s) supported. The MIB module(s) SHOULD be defined concurrently with the procedures which use the MIB module(s). The MIB module(s) are subject to normal access control rules 🚪.
The mapping between the model-dependent security ID and the securityName MUST be able to be determined using SNMP, if the model-dependent MIB is instantiated and if access control policy allows access 🔍.
A.1.5. Cached Security Data 🗄️
For each message received, the Security Model caches the state information such that a Response message can be generated using the same security information, even if the Local Configuration Datastore is altered between the time of the incoming request and the outgoing response ⏳.
A Message Processing Model has the responsibility for explicitly releasing the cached data if such data is no longer needed. To enable this, an abstract securityStateReference data element is passed from the Security Model to the Message Processing Model 🎁.
The cached security data may be implicitly released via the generation of a response, or explicitly released by using the stateRelease primitive, as described in section 4.1 🧹.
A.2. Message Processing Model Design Requirements 📨
An SNMP engine contains a Message Processing Subsystem which may contain multiple Message Processing Models 🏗️.
The Message Processing Model MUST always (conceptually) pass the complete PDU, i.e., it never forwards less than the complete list of varBinds 💯.
A.2.1. Receiving an SNMP Message from the Network 📥
Upon receipt of a message from the network, the Dispatcher in the SNMP engine determines the version of the SNMP message and interacts with the corresponding Message Processing Model to determine the abstract data elements.
A Message Processing Model specifies the SNMP Message format it supports and describes how to determine the values of the abstract data elements (like msgID, msgMaxSize, msgFlags, msgSecurityParameters, securityModel, securityLevel etc). A Message Processing Model interacts with a Security Model to provide security processing for the message using the processMsg primitive, as described in section 4.5 🔐.
A.2.2. Sending an SNMP Message to the Network 📤
The Dispatcher in the SNMP engine interacts with a Message Processing Model to prepare an outgoing message. For that it uses the following primitives:
- for requests and notifications: prepareOutgoingMessage, as described in section 4.4
- for response messages: prepareResponseMessage, as described in section 4.4
A Message Processing Model, when preparing an Outgoing SNMP Message, interacts with a Security Model to secure the message. For that it uses the following primitives:
- for requests and notifications: generateRequestMsg, as described in section 4.5.
- for response messages: generateResponseMsg as described in section 4.5.
Once the SNMP message is prepared by a Message Processing Model, the Dispatcher sends the message to the desired address using the appropriate transport 🎉.
A.3. Application Design Requirements 🧑💻
Within an application, there may be an explicit binding to a specific SNMP message version, i.e., a specific Message Processing Model, and to a specific Access Control Model, but there should be no reference to any data defined by a specific Message Processing Model or Access Control Model 🎀.
Within an application, there should be no reference to any specific Security Model, or any data defined by a specific Security Model 🙅♀️.
An application determines whether explicit or implicit access control should be applied to the operation, and, if access control is needed, which Access Control Model should be used 🔑.
An application has the responsibility to define any MIB module(s) used to provide application-specific services 🧠.
Applications interact with the SNMP engine to initiate messages, receive responses, receive asynchronous messages, and send responses 💬.
A.3.1. Applications that Initiate Messages 🚀
Applications may request that the SNMP engine send messages containing SNMP commands or notifications using the sendPdu primitive as described in section 4.2.
If it is desired that a message be sent to multiple targets, it is the responsibility of the application to provide the iteration 🔁.
The SNMP engine assumes necessary access control has been applied to the PDU, and provides no access control services.
The SNMP engine looks at the "expectResponse" parameter, and if a response is expected, then the appropriate information is cached such that a later response can be associated to this message, and can then be returned to the application. A sendPduHandle is returned to the application so it can later match the response with this message as well 🧾.
A.3.2. Applications that Receive Responses 📬
The SNMP engine matches the incoming response messages to outstanding messages sent by this SNMP engine, and forwards the response to the associated application using the processResponsePdu primitive, as described in section 4.2 💌.
A.3.3. Applications that Receive Asynchronous Messages 📩
When an SNMP engine receives a message that is not the response to a request from this SNMP engine, it must determine to which application the message should be given 🕵️♀️.
An Application that wishes to receive asynchronous messages registers itself with the engine using the primitive registerContextEngineID as described in section 4.2 📝.
An Application that wishes to stop receiving asynchronous messages should unregister itself with the SNMP engine using the primitive unregisterContextEngineID as described in section 4.2.
Only one registration per combination of PDU type and contextEngineID is permitted at the same time. Duplicate registrations are ignored. An errorIndication will be returned to the application that attempts to duplicate a registration ⚠️.
All asynchronously received messages containing a registered combination of PDU type and contextEngineID are sent to the application which registered to support that combination 💖.
The engine forwards the PDU to the registered application, using the processPdu primitive, as described in section 4.2 ✨.
A.3.4. Applications that Send Responses 💌
Request operations require responses. An application sends a response via the returnResponsePdu primitive, as described in section 4.2 🎀.
The contextEngineID, contextName, securityModel, securityName, securityLevel, and stateReference parameters are from the initial processPdu primitive. The PDU and statusInformation are the results of processing 📦.
A.4. Access Control Model Design Requirements 🔑
An Access Control Model determines whether the specified securityName is allowed to perform the requested operation on a specified managed object. The Access Control Model specifies the rules by which access control is determined 🚧.
The persistent data used for access control should be manageable using SNMP, but the Access Control Model defines whether an instantiation of the MIB is a conformance requirement 📒.
The Access Control Model must provide the primitive isAccessAllowed 🏁.
B. Full Copyright Statement ⚖️
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE 🦋🌸
📦 where this page comes from
- ietf: rfc2271 1998-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms