RFC 3411
An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks
Part 1 of 13. More parts are coming, bestie 💖
RFC 3411: An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks 🎀
Okay, the title block is giving main character energy 👑. This one comes from the Network Working Group, and it's written by three people: D. Harrington (Enterasys Networks), R. Presuhn (BMC Software, Inc.), and B. Wijnen (Lucent Technologies). It's dated December 2002, it's RFC 3411, and it's part of STD 62 🌸. The category is Standards Track, so this is an actual official standard, not just a suggestion.
Also, this RFC obsoletes RFC 2571. That means it replaces the older one, so if you're looking at 2571, this is the newer tea ☕.
Status of this Memo ✨
So this document specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 🦋. If you want to know where this protocol actually stands, check the current edition of the "Internet Official Protocol Standards" (STD 1). Also, distribution of this memo is unlimited, so share the link with everyone 💅.
Copyright Notice ✨
Copyright (C) The Internet Society (2002). All Rights Reserved. 🔒
Abstract ✨
Okay, the abstract is basically the big-picture pitch 💖. This document describes an architecture for describing SNMP Management Frameworks, and the whole design is modular so the SNMP protocol standards can keep evolving over time 🌈. The major pieces are an SNMP engine that contains a Message Processing Subsystem, a Security Subsystem, and an Access Control Subsystem. On top of that, you can have multiple SNMP applications that do specific processing of management data. And yes, this document obsoletes RFC 2571 🫶.
Table of Contents ✨
1. Introduction ................................................ 4
1.1. Overview .................................................. 4
1.2. SNMP ...................................................... 5
1.3. Goals of this Architecture ................................ 6
1.4. Security Requirements of this Architecture ................ 6
1.5. Design Decisions .......................................... 8
2. Documentation Overview ...................................... 10
2.1. Document Roadmap .......................................... 11
2.2. Applicability Statement ................................... 11
2.3. Coexistence and Transition ................................ 11
2.4. Transport Mappings ........................................ 12
2.5. Message Processing ........................................ 12
2.6. Security .................................................. 12
2.7. Access Control ............................................ 13
2.8. Protocol Operations ....................................... 13
2.9. Applications .............................................. 14
2.10. Structure of Management Information ...................... 15
2.11. Textual Conventions ...................................... 15
2.12. Conformance Statements ................................... 15
2.13. Management Information Base Modules ...................... 15
2.13.1. SNMP Instrumentation MIBs .............................. 15
2.14. SNMP Framework Documents ................................. 15
3. Elements of the Architecture ................................ 16
3.1. The Naming of Entities .................................... 17
3.1.1. SNMP engine ............................................. 18
3.1.1.1. snmpEngineID .......................................... 18
3.1.1.2. Dispatcher ............................................ 18
3.1.1.3. Message Processing Subsystem .......................... 19
3.1.1.3.1. Message Processing Model ............................ 19
3.1.1.4. Security Subsystem .................................... 20
3.1.1.4.1. Security Model ...................................... 20
3.1.1.4.2. Security Protocol ................................... 20
3.1.2. Access Control Subsystem ................................ 21
3.1.2.1. Access Control Model .................................. 21
3.1.3. Applications ............................................ 21
3.1.3.1. SNMP Manager .......................................... 22
3.1.3.2. SNMP Agent ............................................ 23
3.2. The Naming of Identities .................................. 25
3.2.1. Principal ............................................... 25
3.2.2. securityName ............................................ 25
3.2.3. Model-dependent security ID ............................. 26
3.3. The Naming of Management Information ...................... 26
3.3.1. An SNMP Context ......................................... 28
3.3.2. contextEngineID ......................................... 28
3.3.3. contextName ............................................. 29
3.3.4. scopedPDU ............................................... 29
3.4. Other Constructs .......................................... 29
3.4.1. maxSizeResponseScopedPDU ................................ 29
3.4.2. Local Configuration Datastore ........................... 29
3.4.3. securityLevel ........................................... 29
4. Abstract Service Interfaces ................................. 30
4.1. Dispatcher Primitives ..................................... 30
4.1.1. Generate Outgoing Request or Notification ............... 31
4.1.2. Process Incoming Request or Notification PDU ............ 31
4.1.3. Generate Outgoing Response .............................. 32
4.1.4. Process Incoming Response PDU ........................... 32
4.1.5. Registering Responsibility for Handling SNMP PDUs ....... 32
4.2. Message Processing Subsystem Primitives ................... 33
4.2.1. Prepare Outgoing SNMP Request or Notification Message ... 33
4.2.2. Prepare an Outgoing SNMP Response Message ............... 34
4.2.3. Prepare Data Elements from an Incoming SNMP Message ..... 35
4.3. Access Control Subsystem Primitives ....................... 35
4.4. Security Subsystem Primitives ............................. 36
4.4.1. Generate a Request or Notification Message .............. 36
4.4.2. Process Incoming Message ................................ 36
4.4.3. Generate a Response Message ............................. 37
4.5. Common Primitives ......................................... 37
4.5.1. Release State Reference Information ..................... 37
4.6. Scenario Diagrams ......................................... 38
4.6.1. Command Generator or Notification Originator ............ 38
4.6.2. Scenario Diagram for a Command Responder Application .... 39
5. Managed Object Definitions for SNMP Management Frameworks ... 40
6. IANA Considerations ......................................... 51
6.1. Security Models ........................................... 51
6.2. Message Processing Models ................................. 51
6.3. SnmpEngineID Formats ...................................... 52
7. Intellectual Property ....................................... 52
8. Acknowledgements ............................................ 52
9. Security Considerations ..................................... 54
10. References ................................................. 54
10.1. Normative References ..................................... 54
10.2. Informative References ................................... 56
A. Guidelines for Model Designers .............................. 57
A.1. Security Model Design Requirements ........................ 57
A.1.1. Threats ................................................. 57
A.1.2. Security Processing ..................................... 58
A.1.3. Validate the security-stamp in a received message ....... 59
A.1.4. Security MIBs ........................................... 59
A.1.5. Cached Security Data .................................... 59
A.2. Message Processing Model Design Requirements .............. 60
A.2.1. Receiving an SNMP Message from the Network .............. 60
A.2.2. Sending an SNMP Message to the Network .................. 60
A.3. Application Design Requirements ........................... 61
A.3.1. Applications that Initiate Messages ..................... 61
A.3.2. Applications that Receive Responses ..................... 62
A.3.3. Applications that Receive Asynchronous Messages ......... 62
A.3.4. Applications that Send Responses ........................ 62
A.4. Access Control Model Design Requirements .................. 63
Editors' Addresses ............................................. 63
Full Copyright Statement ....................................... 641. Introduction ✨
1.1. Overview 🌸
Okay, so this document is all about defining a vocabulary for talking about SNMP Management Frameworks, plus an architecture that lays out the major parts of those frameworks 🧚.
Quick heads-up: this is not a beginner's intro to SNMP. There are way better books and docs for that, so go find them 📚. It also doesn't give you the history of SNMP, which, same, that's somewhere else 🙈.
Here's the roadmap, bestie 🗺️:
- Section 1 covers the purpose, goals, and design decisions of this architecture 💖.
- Section 2 covers the different kinds of documents that define (elements of) SNMP Frameworks and how they fit into the architecture. It also gives you a minimal road map to the earlier frameworks docs 🦋.
- Section 3 is the vocabulary deep dive. It's really important for understanding the rest of the sections, and for reading any documents written to fit this architecture 🔥.
- Section 4 describes the primitives used for the abstract service interfaces between the subsystems, models, and applications in this architecture 💅.
- Section 5 defines a collection of managed objects used to instrument SNMP entities here 🌈.
- Sections 6, 7, 8, 9, 10 and 11 are administrative in nature 📋.
- Appendix A has guidelines for designers of Models that are expected to fit this architecture 🎀.
Now the super important part, the key words. 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]. ⭐
Anyway, that's the first chunk 💜. Part 2 is next, so stay tuned!
1.2. SNMP 💖
okay so, an SNMP management system is basically a little team with three parts 🎀:
- several (potentially many) nodes, each holding an SNMP entity with command responder and notification originator applications. These nodes get 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) 👑
- a management protocol that carries the management information between the SNMP entities 💌
SNMP entities that run command generator and notification receiver applications are the ones that monitor and control managed elements ✨. Managed elements are things like hosts, routers, terminal servers, and so on. You keep an eye on them and steer them by getting at their management information 🦋
This document exists to define an architecture that can grow into effective management across all kinds of configurations and environments 🌈. The architecture was built with these implementations in mind:
- 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 kinds of applications, for managing a potentially huge number of managed nodes (traditionally called (network) management stations) 🔥
1.3. Goals of this Architecture 🎯
This architecture was driven by these goals:
- Use existing materials as much as possible. It leans heavily on earlier work, informally known as SNMPv2u and SNMPv2*, which was itself based on SNMPv2p 📚
- Address the need for secure SET support. This is considered the most important deficiency in SNMPv1 and SNMPv2c 🔐
- Make it possible to move portions of the architecture forward on the standards track, even if consensus hasn't been reached on every piece 🛤️
- Define an architecture that allows for longevity of the SNMP Frameworks that have been and will be defined ⏳
- Keep SNMP as simple as possible 🧸
- Make it relatively inexpensive to deploy a minimal 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 that feature 💅
1.4. Security Requirements of this Architecture 🔐
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. Other threats don't apply to management at all. This section covers the principal threats, the secondary threats, and the threats of lesser importance 🙈
The principal threats that any Security Model used within this architecture SHOULD protect against are:
Modification of Information : The modification threat is the danger that some unauthorized 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. 🎭
Secondary threats that any Security Model used within this architecture SHOULD protect against are:
Message Stream Modification : The SNMP protocol is typically based on a connectionless transport service, which can run over any subnetwork service. Messages can get re-ordered, delayed, or replayed through the normal operation of many of those subnetwork services. The message stream modification threat is the danger that messages get maliciously re-ordered, delayed, or replayed to a greater extent than a subnetwork service would naturally do, in order to carry out unauthorized management operations. 🌀
Disclosure : The disclosure threat is the danger of eavesdropping on exchanges between SNMP engines. Protecting against this may be required as a matter of local policy. 👀
There are at least two threats that a Security Model within this architecture does NOT need to protect against, since they're considered less important here:
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, many of these denial-of-service attacks look exactly like the network failures any viable management protocol has to cope with as a matter of course 🤷♀️
Traffic Analysis : A Security Model doesn't need to address traffic analysis attacks. Lots of traffic patterns are predictable (entities are often managed on a regular basis by a relatively small number of management stations), so protecting against traffic analysis doesn't buy you much 📊
1.5. Design Decisions 🧠
Various 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 to 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. As portions of SNMP change over time, the documents describing other portions aren't directly affected. This modularity means that, for example, Security Models, authentication and privacy mechanisms, and message formats can be upgraded and supplemented as needed. The self-contained documents can move along the standards track on different timelines. 📦
This modularity of specification is not meant to be read as imposing any specific requirements on implementation. 💭
- Threats : The Security Models in the Security Subsystem SHOULD protect against the principal and secondary threats: modification of information, masquerade, message stream modification, and disclosure. They don't need to protect against denial of service or traffic analysis. 🛡️
- Remote Configuration : The Security and Access Control Subsystems add a whole new set of SNMP configuration parameters. The Security Subsystem also requires frequent changes of secrets at the various SNMP entities. To make this deployable in a large operational environment, these SNMP parameters MUST be remotely configurable. 🛠️
Note: the original reads "these SNMP parameters must be remotely configurable" in lowercase, so the key word is not a BCP 14 requirement here and is kept as plain prose.
- Controlled Complexity : It's recognized that producers of simple managed devices want to keep the resources SNMP uses 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 lets the more complex environments logically extend the simple one. ⚖️
2. Documentation Overview ✨
okay so before we dive into the nitty-gritty, here's the big map 🗺️🎀 The figure below shows the whole set of documents that fit inside the SNMP Architecture. bestie, it's giving organized chaos but make it aesthetic 💅
+------------------------- 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 | | | | | | |
| | +--------------+ +--------------+ +---------------+ | |
| +---------------------------------------------------------------+ |
| |
| +---------------------------------------------------------------+ |
| | MIB Modules written in various formats, e.g.: | |
| | +----------------+ +----------------+ | |
| | | SMIv1 (STD 18) | | SMIv2 (STD 58) | | |
| | | format | | format | | |
| | +----------------+ +----------------+ | |
| +---------------------------------------------------------------+ |
| |
+-------------------------------------------------------------------+Each of these documents may be replaced or supplemented. This Architecture document specifically describes how new documents fit into the set of documents in the area of Message and PDU handling. 🦋
2.1. Document Roadmap 🗺️
One or more documents may be written to describe how sets of documents taken together form specific Frameworks. The configuration of document sets might change over time, so the "road map" should be maintained in a document separate from the standards documents themselves. ngl this is such a smart move, because nobody wants their map going stale inside the thing it's mapping 🙈
An example of such a roadmap is "Introduction and Applicability Statements for the Internet-Standard Management Framework" [RFC3410]. 💜
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. Some models will be designed to address specific problems of management, such as message security. Different vibes for different situations, iykyk 💅
One or more documents may be written to describe the environments to which certain versions of SNMP or models within SNMP would be appropriately applied, and those to which a given model might be inappropriately applied. So basically, these docs are the "use this here, not there" guides 🫶
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. not me panicking about security holes 😭
The purpose of Coexistence documents is to detail recognized anomalies and to describe required and recommended behaviors for resolving the interactions between models within the architecture. So these are the peacekeepers 🕊️✨
Coexistence documents may be prepared separately from model definition documents, to describe and resolve interaction anomalies between a model definition and one or more other model definitions. Super flexible, honestly iconic 👑
Additionally, recommendations for transitions between models may also be described, either in a coexistence document or in a separate document. 🎀
One such coexistence document is [RFC2576], "Coexistence between Version 1, Version 2, and Version 3 of the Internet-Standard Network Management Framework". 🍓
2.4. Transport Mappings 🚚
SNMP messages are sent over various transports. It is the purpose of Transport Mapping documents to define how the mapping between SNMP and the transport is done. Basically the delivery driver's instructions, and we love a good delivery driver 🧚
2.5. Message Processing 💌
A Message Processing Model document defines a message format, which is typically identified by a version field in an SNMP message header. The document may also define a MIB module for use in message processing and for instrumentation of version-specific interactions. The version field is the little label on the envelope, bestie 💖
An SNMP engine includes one or more Message Processing Models, and thus may support sending and receiving multiple versions of SNMP messages. Multilingual energy, and I'm here for it 🌈
2.6. Security 🔐
Some environments require secure protocol interactions. Security is normally applied at two different stages:
- in the transmission/receipt of messages, and
- in the processing of the contents of messages.
For purposes of this document, "security" refers to message-level security; "access control" refers to the security applied to protocol operations. Two different bouncers, two different doors 🚪✨
Authentication, encryption, and timeliness checking are common functions of message level security. 🔥
A security document describes a Security Model, the threats against which the model protects, the goals of the Security Model, the protocols which it uses to meet those goals, and it may define a MIB module to describe the data used during processing, and to allow the remote configuration of message-level security parameters, such as keys. The full security glow-up writeup 😭🔐
An SNMP engine may support multiple Security Models concurrently. Multitasking queen behavior 👑
2.7. Access Control 🛡️
During processing, it may be required to control access to managed objects for operations. Who's allowed to touch what, and when 💅
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. 🌸
2.8. Protocol Operations 🎀
SNMP messages encapsulate an SNMP Protocol Data Unit (PDU). SNMP PDUs define the operations performed by the receiving SNMP engine. It is the purpose of a Protocol Operations document to define the operations of the protocol with respect to the processing of the PDUs. Every PDU belongs to one or more of the PDU classes defined below: this is where it gets so organized ✨
- Read Class:
The Read Class contains protocol operations that retrieve management information. For example, [RFC3416] defines the following protocol operations for the Read Class: GetRequest-PDU, GetNextRequest-PDU, and GetBulkRequest-PDU. 📖
- Write Class:
The Write Class contains protocol operations which attempt to modify management information. For example, [RFC3416] defines the following protocol operation for the Write Class: SetRequest-PDU. ✏️
- Response Class:
The Response Class contains protocol operations which are sent in response to a previous request. For example, [RFC3416] defines the following for the Response Class: Response-PDU, Report-PDU. 💬
- Notification Class:
The Notification Class contains protocol operations which send a notification to a notification receiver application. For example, [RFC3416] defines the following operations for the Notification Class: Trapv2-PDU, InformRequest-PDU. 🔔
- Internal Class:
The Internal Class contains protocol operations which are exchanged internally between SNMP engines. For example, [RFC3416] defines the following operation for the Internal Class: Report-PDU. 🏠
The preceding five classifications are based on the functional properties of a PDU. It is also useful to classify PDUs based on whether a response is expected: 🧠
- Confirmed Class:
The Confirmed Class contains all protocol operations which cause the receiving SNMP engine to send back a response. For example, [RFC3416] defines the following operations for the Confirmed Class: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, and InformRequest-PDU. "you replied" energy 💌
- Unconfirmed Class:
The Unconfirmed Class contains all protocol operations which are not acknowledged. For example, [RFC3416] defines the following operations for the Unconfirmed Class: Report-PDU, Trapv2-PDU, and GetResponse-PDU. Left on read, but make it protocol 💀
An application document defines which Protocol Operations 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. Little helpers doing the heavy lifting 🫶
An applications document describes 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 document defines which set of documents are used to specifically define the structure of management information, textual conventions, conformance requirements, and operations supported by the application. Every app has its own dress code 👗
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 it as a giant organized closet of objects 🗄️✨
It is the purpose of a Structure of Management Information document to establish the notation for defining objects, modules, and other elements of managed information. The grammar rulebook, 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 documents, or within a MIB module. Custom types with a little 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 the Conformance Statements document to define the notation used for these purposes. Keeping receipts on what "good enough" actually means 🧾💜
2.13. Management Information Base Modules 🎀
okay so MIB documents are basically the lists of managed objects that instrument some aspect of a managed node. it's giving organization and it's honestly so important 💅
2.13.1. SNMP Instrumentation MIBs
bestie, an SNMP MIB document can define a collection of managed objects that instrument the SNMP protocol itself 🦋 And get this, MIB modules can also be defined inside the documents that describe parts of the SNMP architecture, like the documents for Message Processing Models and Security Models. The point is to instrument those Models and to let them be configured remotely. main character energy fr 😭
2.14. SNMP Framework Documents ✨
the whole architecture is built so an SNMP Framework can evolve in an orderly way. slay 👑
for the rest of this document, "subsystem" means an abstract, incomplete spec of a part of a Framework. it gets refined by a model spec 🧚
a "model" is a specific design of a subsystem. it adds extra constraints and rules for conformance to that model. a model is detailed enough that you can actually implement the spec 💜
an "implementation" is an instantiation of a subsystem that conforms to one or more specific models 🌸
SNMP version 1 (SNMPv1) is the original Internet-Standard Network Management Framework. it's described in RFCs 1155, 1157, and 1212 🍓
SNMP version 2 (SNMPv2) is the SNMPv2 Framework, derived from SNMPv1. it's described in STD 58, RFCs 2578, 2579, 2580, and STD 62, RFCs 3416, 3417, and 3418. SNMPv2 has no message definition 🙈
the Community-based SNMP version 2 (SNMPv2c) is an experimental SNMP Framework that supplements SNMPv2, as described in [RFC1901]. it adds the SNMPv2c message format, which is pretty similar to the SNMPv1 message format 🫶
SNMP version 3 (SNMPv3) is an extensible SNMP Framework that supplements SNMPv2 by supporting the following 🔥
- a new SNMP message format,
- Security for Messages,
- Access Control, and
- Remote configuration of SNMP parameters.
other SNMP Frameworks, meaning other configurations of implemented subsystems, are also expected to be consistent with this architecture 🌈
3. Elements of the Architecture ✨
okay this section is where we meet all the pieces of the architecture and how they get named 💖 There are three kinds of naming:
- the naming of entities,
- the naming of identities, and
- the naming of management information.
this architecture also defines some names for other constructs that get used in the documentation 🎀
3.1. The Naming of Entities 🦋
an SNMP entity is an implementation of this architecture. each SNMP entity is made of an SNMP engine plus one or more associated applications 💅
here's the picture of an SNMP entity and everything inside it 👑
+-------------------------------------------------------------------+
| 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 ⭐
an SNMP engine 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 ✨
within an administrative domain, an snmpEngineID is the unique and unambiguous identifier of an SNMP engine. since engines and entities have a one-to-one association, it also uniquely and unambiguously identifies the SNMP entity within that administrative domain 💜
ngl this is a sneaky one: SNMP entities in different administrative domains can have the same snmpEngineID value. federating administrative domains might mean assigning new values 🙈
3.1.1.2. Dispatcher 🦋
there's only one Dispatcher in an SNMP engine. it allows concurrent support of multiple versions of SNMP messages in the engine 🌈 It does this by:
- sending and receiving SNMP messages to and 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 lets them send a PDU to a remote SNMP entity.
3.1.1.3. Message Processing Subsystem 🎀
the Message Processing Subsystem is responsible for preparing messages to send and extracting data from received messages 💖
it can potentially contain multiple Message Processing Models, as shown in the next figure.
* 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 the preparation and extraction of that version-specific message format 🧚
3.1.1.4. Security Subsystem 🔥
the Security Subsystem provides security services like authentication and privacy of messages. it can potentially contain multiple Security Models, as shown in the following figure
* 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 specifies the threats it protects against, the goals of its services, and the security protocols used to provide services like authentication and privacy 💖
3.1.1.4.2. Security Protocol 🫶
a Security Protocol specifies the mechanisms, procedures, and MIB objects used to provide a security service like authentication or privacy 💜
3.1.2. Access Control Subsystem 👑
the Access Control Subsystem provides authorization services through 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, so it can make decisions about access rights 🦋
3.1.3. Applications ✨
okay so there are a few kinds of applications 💅, and they're all the stuff that actually does the work:
- command generators 🔍, which monitor and manipulate management data
- command responders 🎀, which provide access to management data
- notification originators 📣, which start asynchronous messages
- notification receivers 👂, which process asynchronous messages
and
- proxy forwarders 🦋, which forward messages between entities
ngl the applications all lean on the services the SNMP engine gives them. main character energy, but the engine is the real MVP 👑
3.1.3.1. SNMP Manager 💖
so an SNMP entity with one or more command generator and/or notification receiver applications (plus their SNMP engine, obvi) has traditionally been called an SNMP manager 🧚
(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., RFC 3417) | | +->| otherMP * |<--->| +------------+ | |
| +-------------------+ | +------------+ | | | |
| ^ +---------------------+ +----------------+ |
| | |
| v |
+-------------------------------------------------------------------+
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+
^ ^ ^
| | | * One or more models may be present.
v v v
+------------------------------+
| Network |
+------------------------------+3.1.3.2. SNMP Agent 🌸
and an SNMP entity with one or more command responder and/or notification originator applications (plus their SNMP engine) has traditionally been called an SNMP agent 🫶
* One or more models may be present.
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-----+ +-----+ +-------+
| UDP | | IPX | . . . | other |
+-----+ +-----+ +-------+ (traditional SNMP agent)
+-------------------------------------------------------------------+
| ^ |
| | +---------------------+ +----------------+ |
| | | Message Processing | | Security | |
| Dispatcher v | Subsystem | | Subsystem | |
| +-------------------+ | +------------+ | | | |
| | Transport | | +->| v1MP * |<--->| +------------+ | |
| | Mapping | | | +------------+ | | | Other | | |
| | (e.g., RFC 3417) | | | +------------+ | | | 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 🪞
principal
^
|
|
+----------------------------|-------------+
| SNMP engine v |
| +--------------+ |
| | | |
| +-----------------| securityName |---+ |
| | Security Model | | | |
| | +--------------+ | |
| | ^ | |
| | | | |
| | v | |
| | +------------------------------+ | |
| | | | | |
| | | Model | | |
| | | Dependent | | |
| | | Security ID | | |
| | | | | |
| | +------------------------------+ | |
| | ^ | |
| | | | |
| +-------------------------|----------+ |
| | |
| | |
+----------------------------|-------------+
|
v
network3.2.1. Principal 🦋
okay so a principal is the "who" that services are provided for, or whose processing is happening, ya feel? 🥰
a principal can be, among other things: an individual acting in a particular role; a set of individuals, each acting in a particular role; an application or a set of applications; and any combinations of those. it's giving versatile 💅
3.2.2. securityName 💜
a securityName is a human readable string that represents a principal 📝. it has a model-independent format, so it can be used outside of a particular Security Model. iconic ✨
3.2.3. Model-dependent security ID 🌈
a model-dependent security ID is the model-specific way of representing a securityName inside one particular Security Model 🔐
these may or may not be human readable, and they have a model-dependent syntax. examples are community names and user names 🧸
and the transformation between model-dependent security IDs and securityNames (in both directions) is the responsibility of the relevant Security Model. so the model handles the translating, bestie 🫶
3.3. The Naming of Management Information 🎀
Okay so, management info lives at an SNMP entity, and a Command Responder Application there has local access to potentially multiple contexts. This app uses a contextEngineID equal to the snmpEngineID of its SNMP engine. It's giving organized 🧚
+-----------------------------------------------------------------+
| SNMP entity (identified by snmpEngineID, for example: |
| '800002b804616263'H (enterpise 696, string "abc") |
| |
| +------------------------------------------------------------+ |
| | SNMP engine (identified by snmpEngineID) | |
| | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | | | | | | | | | |
| | | Dispatcher | | Message | | Security | | Access | | |
| | | | | Processing | | Subsystem | | Control | | |
| | | | | Subsystem | | | | Subsystem | | |
| | | | | | | | | | | |
| | +-------------+ +------------+ +-----------+ +-----------+ | |
| | | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | Command Responder Application | |
| | (contextEngineID, example: '800002b804616263'H) | |
| | | |
| | example contextNames: | |
| | | |
| | "bridge1" "bridge2" "" (default) | |
| | --------- --------- ------------ | |
| | | | | | |
+--|------------------|-------------------|--------------+ |
| | | |
+------|------------------|-------------------|--------------+ |
| MIB | instrumentation | | | |
| +---v------------+ +---v------------+ +----v-----------+ | |
| | context | | context | | context | | |
| | | | | | | | |
| | +------------+ | | +------------+ | | +------------+ | | |
| | | bridge MIB | | | | bridge MIB | | | | some MIB | | | |
| | +------------+ | | +------------+ | | +------------+ | | |
| | | | | | | | |
| | | | | | +------------+ | | |
| | | | | | | other MIB | | | |
| | | | | | +------------+ | | |
| | | | | | | | |
+-----------------------------------------------------------------+3.3.1. An SNMP Context ✨
Okay bestie, so a 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 a whole bunch of contexts.
There are usually tons of instances of each managed object type in a management domain. To keep things simple, the way the MIB module identifies instances doesn't let each one be told apart from every other instance in the whole domain. Instead, each instance only gets identified within some scope, or "context," and there are multiple of those in the domain. A context is often a physical device or maybe a logical one 🌸 but it can also cover several devices, part of one device, or even part of several devices. The one thing that's always true is that a context is defined as a subset of a single SNMP entity. So to pin down one specific piece 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 [RFC2863] 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") 🦋
Each context has at least one unique identification in the management domain. The same item of management info can exist in multiple contexts, and an item can have multiple unique identifications. That happens when an item lives in multiple contexts, and it also happens when a context has multiple unique identifications. It's a whole web, honestly 🕸️
The combination of a contextEngineID and a contextName unambiguously identifies a context within an administrative domain. Note that there may 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. Non-negotiable, periodt 💅
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 with information named in the context. That context is unambiguously identified within an administrative domain by the combination of the contextEngineID and the contextName. See, for example, RFC 3416 for more info about SNMP PDUs 🌈
3.4. Other Constructs 🌸
3.4.1. maxSizeResponseScopedPDU 🫶
The maxSizeResponseScopedPDU is the maximum size of a scopedPDU that a PDU's sender would be willing to accept. Note that 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 within an SNMP entity may need to keep their own sets of configuration info.
Some of that configuration info may be accessible as managed objects.
The 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:
- 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. Ranked, literally 👑
Every message has an associated securityLevel. All Subsystems (Message Processing, Security, Access Control) and applications are REQUIRED to either supply a value of securityLevel or to abide by the supplied value of securityLevel while processing the message and its contents. No excuses, bestie 😭
4. Abstract Service Interfaces 🦋
Abstract service interfaces have been defined to describe the conceptual interfaces between the various subsystems within an SNMP entity. They're meant to help clarify the externally observable behavior of SNMP entities, and they're not meant to constrain how implementations are structured or organized in any way. Most specifically, they should not be interpreted as APIs or as requirements statements for APIs. ✨
These abstract service 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 via its PDU Dispatcher. This section describes the primitives provided by the PDU Dispatcher. 🧚
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 return an SNMP Response PDU to the PDU Dispatcher:
result = -- SUCCESS or FAILURE
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 sender can accept
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 ✨
okay so the PDU Dispatcher has this one primitive, processResponsePdu, that hands an incoming SNMP Response PDU up to an application 💌 it's giving "here's your reply, bestie" 🫶
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 🎀
ngl this part is so cute 🥹 applications can sign up to be responsible for a specific contextEngineID and for specific pduTypes, and they can also tap out and unregister later 💅 the pduTypes you're allowed to sign up for depend on the Message Processing Model(s) that the SNMP entity holding the PDU Dispatcher supports, so it's not a free-for-all 🌸
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
)Also, the realizations of registerContextEngineID and unregisterContextEngineID are allowed to offer their own implementation-specific ways to register and deregister for all possible values of the contextEngineID or pduType parameters 🦋 so the implementation can get creative with the wildcard energy 💜
4.2. Message Processing Subsystem Primitives 🧚
okay so the Dispatcher works with a Message Processing Model to handle one specific version of an SNMP Message 🍓 this section is the lineup of primitives that the Message Processing Subsystem gives you for that job 💖
4.2.1. Prepare Outgoing SNMP Request or Notification Message 📤
the Message Processing Subsystem gives you this service primitive to get an outgoing SNMP Request or Notification Message ready to go 🚀
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 💌
this is the primitive for prepping an outgoing SNMP Response Message 🫧
result = -- SUCCESS or FAILURE
prepareResponseMessage(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- same as on incoming request
IN securityName -- same as on incoming request
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size able to accept
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 🔍
this one takes an incoming SNMP message and breaks it down into its abstract data elements 🧩 it's basically the unboxing moment 🎁
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 sender can accept
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 main clients of the Access Control Subsystem, so this is where they go to ask "am I allowed to do this?" 👑
the one primitive here is isAccessAllowed, which checks 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 usual client of the Security Subsystem, so it's the one doing most of the asking here 💅
4.4.1. Generate a Request or Notification Message 🔒
the Security Subsystem gives you this primitive to generate a Request or Notification message 📨
statusInformation =
generateRequestMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)4.4.2. Process Incoming Message 📥
this is the primitive the Security Subsystem uses to process an incoming message 🧁
statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
OUT securityEngineID -- authoritative SNMP entity
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size sender can handle
OUT securityStateReference -- reference to security state
) -- information, needed for response4.4.3. Generate a Response Message 📬
and this is the primitive for generating a Response message, so the reply gets packaged up properly 🎀
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, so everybody gets a piece of the action ✨
4.5.1. Release State Reference Information 🧹
any Subsystem that passes stateReference information around also gets a primitive for releasing the memory holding that state information 🧼 so nothing gets left behind, periodt 💀
stateRelease(
IN stateReference -- handle of reference to be released
)4.6. Scenario Diagrams 🦋
4.6.1. Command Generator or Notification Originator
okay so this diagram shows how a Command Generator or Notification Originator app asks for a PDU to be sent 📨, and how the response gets handed back to that app (asynchronously, so it's not just sitting there waiting 🦋) ✨
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
this one is the Command Responder or Notification Receiver side 🧚 It shows how the app registers for handling a pduType 💅, how a PDU gets dispatched to it after an SNMP message comes in 📬, and how the Response is sent back out 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 🎀
the MIB module starts here, and it's giving formal vibes 💅 Every line below is copied exactly, so it's the real deal 🔥
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 "200210140000Z"
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-EMail: snmpv3@lists.tislabs.com
Subscribe: snmpv3-request@lists.tislabs.com
Co-Chair: Russ Mundy
Network Associates Laboratories
postal: 15204 Omega Drive, Suite 300
Rockville, MD 20850-4601
USA
EMail: mundy@tislabs.com
phone: +1 301-947-7107
Co-Chair &
Co-editor: David Harrington
Enterasys Networks
postal: 35 Industrial Way
P. O. Box 5005
Rochester, New Hampshire 03866-5005
USA
EMail: dbh@enterasys.com
phone: +1 603-337-2614
Co-editor: Randy Presuhn
BMC Software, Inc.
postal: 2141 North First Street
San Jose, California 95131
USA
EMail: randy_presuhn@bmc.com
phone: +1 408-546-1006
Co-editor: Bert Wijnen
Lucent Technologies
postal: Schagen 33
3461 GL Linschoten
Netherlands
EMail: bwijnen@lucent.com
phone: +31 348-680-485
"
DESCRIPTION "The SNMP Management Architecture MIB
Copyright (C) The Internet Society (2002). This
version of this MIB module is part of RFC 3411;
see the RFC itself for full legal notices.
"
REVISION "200210140000Z" -- 14 October 2002
DESCRIPTION "Changes in this revision:
- Updated various administrative information.
- Corrected some typos.
- Corrected typo in description of SnmpEngineID
that led to range overlap for 127.
- Changed '255a' to '255t' in definition of
SnmpAdminString to align with current SMI.
- Reworded 'reserved' for value zero in
DESCRIPTION of SnmpSecurityModel.
- The algorithm for allocating security models
should give 256 per enterprise block, rather
than 255.
- The example engine ID of 'abcd' is not
legal. Replaced with '800002b804616263'H based
on example enterprise 696, string 'abc'.
- Added clarification that engineID should
persist across re-initializations.
This revision published as RFC 3411.
"
REVISION "199901190000Z" -- 19 January 1999
DESCRIPTION "Updated editors' addresses, fixed typos.
Published as RFC 2571.
"
REVISION "199711200000Z" -- 20 November 1997
DESCRIPTION "The initial version, published in RFC 2271.
"
::= { snmpModules 10 }
-- Textual Conventions used in the SNMP Management Architecture ***okay bestie, we're getting into the textual conventions now and these are so detailed 💅
SnmpEngineID ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
Objects of this type are for identification, not for
addressing, even though it is possible that an
address may have been used in the generation of
a specific value.
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 string 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
128-255 - as defined by the enterprise
Maximum remaining length 27
"
SYNTAX OCTET STRING (SIZE(5..32))next up: the security model identifiers, and these ones have some really fun math 🧚
SnmpSecurityModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a
Security Model of the Security Subsystem within
this SNMP Management Architecture.
The values for securityModel are allocated as
follows:
- The zero value does not identify any particular
security model.
- 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
259.
This scheme for allocation of securityModel
values allows for a maximum of 255 standards-
based Security Models, and for a maximum of
256 Security Models per enterprise.
It is believed that the assignment of new
securityModel values will be rare in practice
because the larger the number of simultaneously
utilized Security Models, the larger the
chance that interoperability will suffer.
Consequently, it is believed that such a range
will be sufficient. In the unlikely event that
the standards committee finds this number to be
insufficient over time, an enterprise number
can be allocated to obtain an additional 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
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)okay the message processing model one is basically the same vibe, just with its own little list 🌸
SnmpMessageProcessingModel ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION "An identifier that uniquely identifies a Message
Processing Model of the Message Processing
Subsystem within this 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 259.
This scheme for allocating messageProcessingModel
values allows for a maximum of 255 standards-
based Message Processing Models, and for a
maximum of 256 Message Processing Models per
enterprise.
It is believed that the assignment of new
messageProcessingModel values will be rare
in practice because the larger the number of
simultaneously utilized Message Processing Models,
the larger the chance that interoperability
will suffer. It is believed that such a range
will be sufficient. In the unlikely event that
the standards committee finds this number to be
insufficient over time, an enterprise number
can be allocated to obtain an additional 256
possible values.
Note that the most significant bit must be zero;
hence, there are 23 bits allocated for various
organizations to design and define non-standard
messageProcessingModels. This limits the ability
to define new proprietary implementations of
Message Processing Models to the first 8,388,608
enterprises.
It is worthwhile to note that, in its encoded
form, the messageProcessingModel 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)last one for this batch: the security levels, which are ordered so you can compare them 🎀
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 "255t"
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 [RFC2279].
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. Byte sequences that do not
correspond to the valid UTF-8 encoding of a
code point or are outside this range are
prohibited.
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.
UTF-8 may require multiple bytes to represent a
single character / code point; thus the length
of this object in octets may be different from
the number of characters encoded. Similarly,
size constraints refer to the number of encoded
octets, not the number of characters represented
by an 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
[RFC3416].
Note that the size of an SnmpAdminString object is
measured in octets, not characters.
"
SYNTAX OCTET STRING (SIZE (0..255))
-- Administrative assignments ***************************************
snmpFrameworkAdmin
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 1 }
snmpFrameworkMIBObjects
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 2 }
snmpFrameworkMIBConformance
OBJECT IDENTIFIER ::= { snmpFrameworkMIB 3 }
-- the snmpEngine Group ********************************************
snmpEngine OBJECT IDENTIFIER ::= { snmpFrameworkMIBObjects 1 }
snmpEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-only
STATUS current
DESCRIPTION "An SNMP engine's administratively-unique identifier.
This information SHOULD be stored in non-volatile
storage so that it remains constant across
re-initializations of the SNMP engine.
"
::= { 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 snmpEngineID
was last configured.
"
::= { snmpEngine 2 }
snmpEngineTime OBJECT-TYPE
SYNTAX INTEGER (0..2147483647)
UNITS "seconds"
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of seconds since the value of
the snmpEngineBoots object last changed.
When incrementing this object's value would
cause it to exceed its maximum,
snmpEngineBoots is incremented as if a
re-initialization had occurred, and this
object's value consequently reverts to zero.
"
::= { 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 }
-- 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. IANA Considerations ✨
okay so IANA is going to be looking after three number spaces 🦋 one for security models, one for message processing models, and one for SnmpEngineID formats 💖
6.1. Security Models
the SnmpSecurityModel TEXTUAL-CONVENTION values that IANA manages live in the range from 0 to 255 inclusive 🎀 and they're reserved for standards-track Security Models 💅 if that range ever turns out to be not enough, an enterprise number can be allocated to get an extra 256 possible values 🌈
as of writing, there are a few securityModel values already defined for use with SNMP or reserved for supporting MIB objects 🧚 here they are:
0 reserved for 'any'
1 reserved for SNMPv1
2 reserved for SNMPv2c
3 User-Based Security Model (USM)6.2. Message Processing Models
the SnmpMessageProcessingModel TEXTUAL-CONVENTION values that IANA manages are in the range 0 to 255, inclusive ✨ each value uniquely identifies a standards-track Message Processing Model of the Message Processing Subsystem within the SNMP Management Architecture 👑
if this range ever proves insufficient, an enterprise number may be obtained for the standards committee to get an additional 256 possible values 🫶
as of writing, there are a few messageProcessingModel values defined for use with SNMP 🍓 they go like this:
0 reserved for SNMPv1
1 reserved for SNMPv2c
2 reserved for SNMPv2u and SNMPv2*
3 reserved for SNMPv36.3. SnmpEngineID Formats
the SnmpEngineID TEXTUAL-CONVENTION's fifth octet holds a format identifier 🦋 the values IANA manages are in the range 6 to 127, inclusive 💜 each value uniquely identifies a standards-track SnmpEngineID format 🌸
7. Intellectual Property ✨
okay real talk bestie, the IETF takes no position on whether any intellectual property or other rights that somebody might claim about this tech are valid or how far they reach 💅 it also doesn't say whether any licence under those rights is or isn't available, and it doesn't claim it went looking for any of them 🙈
info on the IETF's rules for rights in standards-track and standards-related docs is in RFC 2028 📚 copies of claims of rights made available for publication, plus any assurances of licences to be made available, or the result of an attempt to get a general licence or permission for implementors or users to use those proprietary rights, can all be grabbed from the IETF Secretariat 🎀
and the IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that might cover tech that may be required to practise this standard 🫶 send that info to the IETF Executive Director 👑
8. Acknowledgements 🫶
okay bestie, time to give credit where it's due, because so many people made this happen. This document is the result of the efforts of the SNMPv3 Working Group. Some special thanks go to these SNMPv3 WG members:
- Harald Tveit Alvestrand (Maxware)
- Dave Battle (SNMP Research, Inc.)
- Alan Beard (Disney Worldwide Services)
- Paul Berrevoets (SWI Systemware/Halcyon Inc.)
- Martin Bjorklund (Ericsson)
- Uri Blumenthal (IBM T.J. Watson Research Center)
- Jeff Case (SNMP Research, Inc.)
- John Curran (BBN)
- Mike Daniele (Compaq Computer Corporation)
- T. Max Devlin (Eltrax Systems)
- John Flick (Hewlett Packard)
- Rob Frye (MCI)
- Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.)
- David Harrington (Cabletron Systems Inc.)
- Lauren Heintz (BMC Software, Inc.)
- N.C. Hien (IBM T.J. Watson Research Center)
- Michael Kirkham (InterWorking Labs, Inc.)
- Dave Levi (SNMP Research, Inc.)
- Louis A Mamakos (UUNET Technologies Inc.)
- Joe Marzot (Nortel Networks)
- Paul Meyer (Secure Computing Corporation)
- Keith McCloghrie (Cisco Systems)
- Bob Moore (IBM)
- Russ Mundy (TIS Labs at Network Associates)
- Bob Natale (ACE*COMM Corporation)
- Mike O'Dell (UUNET Technologies Inc.)
- Dave Perkins (DeskTalk)
- Peter Polkinghorne (Brunel University)
- Randy Presuhn (BMC Software, Inc.)
- David Reeder (TIS Labs at Network Associates)
- David Reid (SNMP Research, Inc.)
- Aleksey Romanov (Quality Quorum)
- Shawn Routhier (Epilogue)
- Juergen Schoenwaelder (TU Braunschweig)
- Bob Stewart (Cisco Systems)
- Mike Thatcher (Independent Consultant)
- Bert Wijnen (IBM T.J. Watson Research Center)
The document is based on recommendations of the IETF Security and Administrative Framework Evolution for SNMP Advisory Team. Members of that Advisory Team were:
- David Harrington (Cabletron Systems Inc.)
- Jeff Johnson (Cisco Systems)
- David Levi (SNMP Research Inc.)
- John Linn (Openvision)
- Russ Mundy (Trusted Information Systems) chair
- Shawn Routhier (Epilogue)
- Glenn Waters (Nortel)
- Bert Wijnen (IBM T. J. Watson Research Center)
As recommended by the Advisory Team and the SNMPv3 Working Group Charter, the design incorporates as much as practical from previous RFCs and drafts. So a huge shoutout 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.)
9. Security Considerations 🔐
okay this part is SERIOUS, so read it slowly 👀. This document describes how an implementation can include a Security Model to protect management messages, and an Access Control Model to control access to management information.
The level of security you get is determined by the specific Security Model implementation(s) and the specific Access Control Model implementation(s) you use. So choose wisely 💅.
Applications have access to data that is not secured. Applications SHOULD take reasonable steps to protect the data from disclosure. No cap, this one matters a lot 😭.
It is the responsibility of the purchaser of an implementation to make sure that:
- an implementation complies with the rules defined by this architecture,
- the Security and Access Control Models utilized satisfy the security and access control needs of the organization,
- the implementations of the Models and Applications comply with the model and application specifications,
- and the implementation protects configuration secrets from inadvertent disclosure.
This document also contains a MIB definition module. None of the objects defined is writable, and the information they represent is not deemed to be particularly sensitive. However, if they are deemed sensitive in a particular environment, access to them should be restricted through the use of appropriately configured Security and Access Control models. Main character energy for the MIB objects: read-only, but still guard them if they're sensitive 🛡️✨
10. References 📚
10.1. Normative References
These are the must-read ones, the foundation of the whole vibe 💜:
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Structure of Management
Information Version 2 (SMIv2)", STD 58, RFC 2578, April
1999.
[RFC2579] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Textual Conventions for
SMIv2", STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M. and S. Waldbusser, "Conformance Statements for
SMIv2", STD 58, RFC 2580, April 1999.
[RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen,
"Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002.
[RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, RFC
3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "User-Based Security Model
(USM) for Version 3 of the Simple Network Management
Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
[RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415, December
2002.
[RFC3416] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Protocol Operations for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3416, December
2002.
[RFC3417] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Transport Mappings for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3417, December
2002.
[RFC3418] Presuhn, R., Case, J., McCloghrie, K., Rose, M. and S.
Waldbusser, "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62, RFC
3418, December 2002.10.2. Informative References
These ones are the extra reading for when you want the backstory 🧚:
[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.
[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.
[RFC2576] Frye, R., Levi, D., Routhier, S. and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3
of the Internet-Standard Network Management Framework",
RFC 2576, March 2000.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, June 2000.
[RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.Appendix A 📎
A. Guidelines for Model Designers 🎀
This appendix is the cheat sheet for anyone designing models that are meant to fit into this architecture 🧁.
SNMPv1 and SNMPv2c are two SNMP frameworks that use communities to provide trivial authentication and access control. SNMPv1 and SNMPv2c Frameworks can coexist with Frameworks designed according to this architecture, and modified versions of SNMPv1 and SNMPv2c Frameworks could be designed to meet the requirements of this architecture, but this document does not provide guidelines for that coexistence.
Within any subsystem model, there should be no reference to any specific model of another subsystem, or to data defined by a specific model of another subsystem. Keep your borders clean, bestie 🙅♀️.
Transfer of data between the subsystems is deliberately described as a fixed set of abstract data elements and primitive functions, which can be overloaded to satisfy the needs of multiple model definitions. Very intentional, very iconic 💖.
Documents which define models to be used within this architecture SHOULD use the standard primitives between subsystems, possibly defining specific mechanisms for converting the abstract data elements into model-usable formats. This constraint exists to allow subsystem and model documents to be written recognizing common borders of the subsystem and model. Vendors are not constrained to recognize these borders in their implementations, so they can do their own thing under the hood 🧚.
The architecture defines certain standard services to be provided between subsystems, and the architecture defines abstract service interfaces to request these services.
Each model definition for a subsystem SHOULD support the standard service interfaces, but whether, or how, or how well, it performs the service is dependent on the model definition. Ngl, the "how well" part is where the drama lives 🍓.
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. Non-negotiable, periodt 👑.
A.1.2. Security Processing ✨
Okay so every received message MUST be validated by a Model of the Security Subsystem 🔐. That validation includes authentication and privacy processing if needed, but it's explicitly allowed to send messages that don't need authentication or privacy. Not everything has to be locked down, bestie 🦋
A received message carries a specified securityLevel that gets used during processing. All messages requiring privacy MUST also require authentication. Privacy without auth is a no-go 🙅♀️
A Security Model defines the rules for how authentication and privacy get done. A model can add extra security features, but it's limited to using (possibly a subset of) the abstract data elements defined in this document for passing data between subsystems 💅
Each Security Model may allow multiple security protocols to be used concurrently inside an implementation of the model. Each one defines how to figure out which protocol to use, given the securityLevel and the security parameters relevant to the message. Each Security Model, together with its protocol(s), defines how the sending and receiving entities are identified and how secrets are configured 🗝️
Authentication and Privacy protocols supported by Security Models are uniquely identified using Object Identifiers. IETF standard protocols should have an identifier defined within the snmpAuthProtocols or 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 processIncomingMsg primitive as described in section 4.4.2 ✨
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 so 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. Main character energy 👑
A Message Processing Model has the responsibility for explicitly releasing the cached data if that data is no longer needed. To make this possible, 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 4.5.1 🌸
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. No shortcuts, periodt 💅
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). It interacts with a Security Model to provide security processing for the message using the processIncomingMsg primitive, as described in section 4.4.2 🔍
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 4.2.1. - for response messages:
prepareResponseMessage, as described in section 4.2.2.
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 4.4.1. - for response messages:
generateResponseMsg, as described in section 4.4.3.
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 4.1.1 ✨
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. That's on the app, not the engine 💁♀️
The SNMP engine looks at the "expectResponse" parameter. If a response is expected, the appropriate information is cached so that a later response can be associated with this message and then 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 4.1.4 🫶
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 registerContextEngineID primitive, as described in section 4.1.5 📝
An Application that wishes to stop receiving asynchronous messages should unregister itself with the SNMP engine using the unregisterContextEngineID primitive, as described in section 4.1.5 👋
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. Not doing the same thing twice, bestie 🙅♀️
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 4.1.2 🎯
A.3.4. Applications that Send Responses 📬
Request operations require responses. An application sends a response via the returnResponsePdu primitive, as described in section 4.1.3 💖
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 🧚
Editors' Addresses 💌
Bert Wijnen
Lucent Technologies
Schagen 33
3461 GL Linschoten
Netherlands
Phone: +31 348-680-485
EMail: bwijnen@lucent.com
David Harrington
Enterasys Networks
Post Office Box 5005
35 Industrial Way
Rochester, New Hampshire 03866-5005
USA
Phone: +1 603-337-2614
EMail: dbh@enterasys.com
Randy Presuhn
BMC Software, Inc.
2141 North First Street
San Jose, California 95131
USA
Phone: +1 408-546-1006
Fax: +1 408-965-0359
EMail: randy_presuhn@bmc.comFull Copyright Statement ✨
okay so the legal bit, bestie 💅 Here's the copyright line, verbatim: Copyright (C) The Internet Society (2002). All Rights Reserved. 🦋
You're allowed to copy and share this document, and to translate it, as long as the copyright notice and this paragraph stay on every copy. You can also make derivative works that comment on or explain it, or help people implement it, and publish and distribute those too, in whole or in part, with no restrictions of any kind. The catch: the document itself can't be modified in any way. You can't remove the copyright notice, and you can't remove references to the Internet Society or other Internet organizations. The exceptions are when you need it for developing Internet standards (then the copyright procedures in the Internet Standards process must be followed) or when you're translating it into a language other than English 🌸
These permissions are perpetual, so the Internet Society and its successors or assigns won't take them back. Lowkey iconic 👑
Now the disclaimer, which is serious even though I'm having fun with it 💀 The document and everything in it 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. Translation: no promises, no guarantees, so be careful and check your own work 🙈
Acknowledgement 🫶
Last one, and it's a sweet one 🥹 Funding for the RFC Editor function is currently provided by the Internet Society. So the people who keep these documents organized and published are being supported by the Internet Society right now 🧚💜
📦 where this page comes from
- ietf: rfc3411 2002-12
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms