Some basic concepts

• SNMP protocol

  Simple Network Management Protocol (SNMP) is an application layer protocol of the TCP/IP protocol cluster. It was developed in 1988 and adopted by the Internet Architecture Board (IAB) as a short-term network management solution; due to the simplicity of SNMP, it has flourished in the Internet era, and SNMPv2 was released in 1992 to enhance the security and functionality of SNMPv1. Now, an SNMPv3 version is available.
  A complete SNMP system consists of a Management Information Base (MIB), Management Information Structure (SMI), and SNMP message protocols.

• The MIB (Management Information Base)

  Any managed resource is represented as an object, called a managed object.MIB is a collection of managed objects. It defines a set of properties of the managed object: the object’s name, the object’s access rights, the object’s data type, etc. Each SNMP device (Agent) has its own MIB. Each SNMP device (Agent) has its own MIB, which can also be seen as a communication bridge between the NMS (Network Management System) and the Agent. The relationship between them is shown in Figure 1.

  

• SNMP messages

  SNMP specifies five types of protocol data unit PDUs (also known as SNMP messages) to be exchanged between the management process and the proxy.

    - get-request (abbreviation: GET): extracts one or more parameter values from the proxy process.
    - get-next-request (abbreviated GET-NEXT): extract the next parameter value immediately following the current parameter value from the proxy process.
    - set-request (SET): Set one or more parameter values for the proxy process.
    - get-response: one or more parameter values to be returned. This operation is issued by the proxy process and is the response to the previous three operations.
    - trap operation: a message initiated by the proxy process that notifies the management process that something is happening.
  

Data Types in MIB

-- the "base types" defined here are:
-- 3 built-in ASN.1 types: INTEGER, OCTET STRING, OBJECT IDENTIFIER
-- 8 application-defined types: Integer32, IpAddress, Counter32,
-- Gauge32, Unsigned32, TimeTicks, Opaque, and Counter64

• Type Definitions

Details: following OID DataTypes

• Integer: Signed 32bit Integer (values between - 2147483648 and 2147483647).
• OctetString：Arbitrary binary or textual data, typically limited to 255 characters in length.
• OctetString：Arbitrary binary or textual data, typically limited to 255 characters in length.
• IPAddress: An IP address.
• Counter32: Represents a non-negative integer which monotonically increases until it reaches a maximum value of 32bits-1 (4294967295 dec), when it wraps around and starts increasing again from zero.
• Counter64: Same as Counter32 but has a maximum value of 64bits-1.
• Gauge32: Represents an unsigned integer, which may increase or decrease, but shall never exceed a maximum value.
• TimeTicks: Represents an unsigned integer which represents the time, modulo 2³² (4294967296 dec), in hundredths of a second between two epochs.
• Opaque: Provided solely for backward-compatibility, its no longer used.

Communities of exchange

• [Google Group] (https://groups.google.com/forum/?hl=zh-CN?hl%3Den#!forum/ems-nms)

Reference

• Introduction to Digital Ocean )
• [SNMP protocol explained in detail (it’s not really detailed, just that it’s barely working)] (https://blog.csdn.net/shanzhizi/article/details/11606767)