1  SNMP Introduction

1 SNMP Introduction

The SNMP development toolkit contains the following parts:

  • An Extensible multi-lingual SNMP agent, which understands SNMPv1 (RFC1157), SNMPv2c (RFC1901, 1905, 1906 and 1907), SNMPv3 (RFC2271, 2272, 2273, 2274 and 2275), or any combination of these protocols.
  • A multi-lingual SNMP manager.
  • A MIB compiler, which understands SMIv1 (RFC1155, 1212, and 1215) and SMIv2 (RFC1902, 1903, and 1904).

The SNMP development tool provides an environment for rapid agent/manager prototyping and construction. With the following information provided, this tool is used to set up a running multi-lingual SNMP agent/manager:

  • a description of a Management Information Base (MIB) in Abstract Syntax Notation One (ASN.1)
  • instrumentation functions for the managed objects in the MIB, written in Erlang.

The advantage of using an extensible (agent/manager) toolkit is to remove details such as type-checking, access rights, Protocol Data Unit (PDU), encoding, decoding, and trap distribution from the programmer, who only has to write the instrumentation functions, which implement the MIBs. The get-next function only has to be implemented for tables, and not for every variable in the global naming tree. This information can be deduced from the ASN.1 file.

This manual describes the SNMP development tool, as a component of the Erlang/Open Telecom Platform development environment. It is assumed that the reader is familiar with the Erlang Development Environment, which is described in a separate User's Guide.

The following prerequisites is required for understanding the material in the SNMP User's Guide:

  • the basics of the Simple Network Management Protocol version 1 (SNMPv1)
  • the basics of the community-based Simple Network Management Protocol version 2 (SNMPv2c)
  • the basics of the Simple Network Management Protocol version 3 (SNMPv3)
  • the knowledge of defining MIBs using SMIv1 and SMIv2
  • familiarity with the Erlang system and Erlang programming

The tool requires Erlang release 4.7 or later.

The following definitions are used in the SNMP User's Guide.

MIB
The conceptual repository for management information is called the Management Information Base (MIB). It does not hold any data, merely a definition of what data can be accessed. A definition of an MIB is a description of a collection of managed objects.
SMI
The MIB is specified in an adapted subset of the Abstract Syntax Notation One (ASN.1) language. This adapted subset is called the Structure of Management Information (SMI).
ASN.1
ASN.1 is used in two different ways in SNMP. The SMI is based on ASN.1, and the messages in the protocol are defined by using ASN.1.
Managed object

A resource to be managed is represented by a managed object, which resides in the MIB. In an SNMP MIB, the managed objects are either:

  • scalar variables, which have only one instance per context. They have single values, not multiple values like vectors or structures.
  • tables, which can grow dynamically.
  • a table element, which is a special type of scalar variable.
Operations
SNMP relies on the three basic operations: get (object), set (object, value) and get-next (object).
Instrumentation function
An instrumentation function is associated with each managed object. This is the function, which actually implements the operations and will be called by the agent when it receives a request from the management station.
Manager
A manager generates commands and receives notifications from agents. There usually are only a few managers in a system.
Agent
An agent responds to commands from the manager, and sends notification to the manager. There are potentially many agents in a system.

In addition to this introductory chapter, the SNMP User's Guide contains the following chapters:

  • Chapter 2: "Functional Description" describes the features and operation of the SNMP development toolkit. It includes topics on Sub-agents and MIB loading, Internal MIBs, and Traps.
  • Chapter 3: "The MIB Compiler" describes the features and the operation of the MIB compiler.
  • Chapter 4: "Running the application" describes how to start and configure the application. Topics on how to debug the application are also included.
  • Chapter 5: "Definition of Agent Configuration Files" is a reference chapter, which contains more detailed information about the agent configuration files.
  • Chapter 6: "Definition of Manager Configuration Files" is a reference chapter, which contains more detailed information about the manager configuration files.
  • Chapter 7: "Agent Implementation Example" describes how an MIB can be implemented with the SNMP Development Toolkit. Implementation examples are included.
  • Chapter 8: "Instrumentation Functions" describes how instrumentation functions should be defined in Erlang for the different operations.
  • Chapter 9: "Definition of Instrumentation Functions" is a reference chapter which contains more detailed information about the instrumentation functions.
  • Chapter 10: "Definition of Agent Net if" is a reference chapter, which describes the Agent Net if function in detail.
  • Chapter 11: "Definition of Manager Net if" is a reference chapter, which describes the Manager Net if function in detail.
  • Chapter 12: "Advanced Agent Topics" describes sub-agents, agent semantics, audit trail logging, and the consideration of distributed tables.
  • Appendix A describes the conversion of SNMPv2 to SNMPv1 error messages.
  • Appendix B contains the RFC1903 text on RowStatus.

Refer to the following documentation for more information about SNMP and about the Erlang/OTP development system:

  • Marshall T. Rose (1991), "The Simple Book - An Introduction to Internet Management", Prentice-Hall
  • Evan McGinnis and David Perkins (1997), "Understanding SNMP MIBs", Prentice-Hall
  • RFC1155, 1157, 1212 and 1215 (SNMPv1)
  • RFC1901-1907 (SNMPv2c)
  • RFC1908, 2089 (coexistence between SNMPv1 and SNMPv2)
  • RFC2271, RFC2273 (SNMP std MIBs)
  • the Mnesia User's Guide
  • the Erlang 4.4 Extensions User's Guide
  • the Reference Manual
  • the Erlang Embedded Systems User's Guide
  • the System Architecture Support Libraries (SASL) User's Guide
  • the Installation Guide
  • the Asn1 User's Guide
  • Concurrent Programming in Erlang, 2nd Edition (1996), Prentice-Hall, ISBN 0-13-508301-X.

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