This page is intended to provide a troubleshooting process for problems involving SNMP, such as SNMP configuration validation, snmpd daemon status, port, rules, traffic captures, mibs translations, possible failures/errors. 

What is SNMP?

SNMP stands for Simple Network Management Protocol and consists of three key components: managed devices, agents and network management systems. The protocol is a set of standards for communicating with devices on a TCP/IP network. It can be defined as an application-level protocol designed to monitor network infrastructure and provides administrators with device-centric visibility. SNMP monitoring is useful for anyone responsible for servers and network devices such as servers, routers, hubs, switches, ups, etc.

How to troubleshoot SNMP communication issues

There are a number of reasons may not be able to communicate with a device during discovery, or communication could be lost some time later. There are things you can check to verify proper SNMP communication.

Device Troubleshooting Process

General Troubleshooting

Start with these basic checks:

Ports/rules required by the snmpd service.

SNMP operates at the application layer of the Internet protocol suite (layer 7 of the OSI model).

The ports commonly used for SNMP are as follows:

for more references click here

snmpd daemon status validation

Procedure to validate if the snmpd daemon is correctly found on the NMIS server.

NMIS server snmp configuration

Tutorial on how to configure SNMP to monitor our server, we will focus on CentOS as it is one of the most widespread distributions for servers. Except for the installation, the rest is similar in other distributions.

configuration steps.

Snmp queries to devices

The most widely used SNMP versions are SNMP version 1 (SNMPv1) and SNMP version 2 (SNMPv2). SNMP version 3 (SNMPv3) includes important changes with respect to previous versions, especially in security issues; however, its acceptance has been very low due to some implementation problems and incompatibilities.
The snmpwalk command will be used for these queries.

Examples of command execution.

SNMPBULKWALK

snmpbulkwalk is an SNMP application that uses SNMP GETBULK requests to query a network entity efficiently for a tree of information.

More details here.

Procedure for translating MIBS

One of the most common issues that users encounter with SNMP Traps and MIB files are that most MIB files require other MIB files to be loaded on the system so they can be fully translated. Solving this issue require that those needed MIB files are gathered and translated appropriately.

Details of the procedure.

SNMP trap

SNMP traps are one of the oldest standards for fault notification on network equipment. As one of the oldest standard protocols, most network devices with basic management capabilities typically support SNMP traps. When a device detects an error or change, the device will send a notification to one or more trap receivers.
NMIS waits for incoming messages and upon receiving data and, depending on the filtering rule, sound the alarm to notify of this detected event.

Tests for snmptraps reception.