SNMP Manager, Agent, Messages and Commands

5 min

SNMP is essential for monitoring and managing network devices efficiently.

This article explores the four critical components of SNMP: the Manager, the Agent, the Messages, and the Commands. Understanding these elements is key to leveraging SNMP for effective network management. Whether you’re new to network technologies or an experienced professional, this guide will enhance your understanding of how SNMP works.

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In short,  SNMP (Simple Network Management Protocol) monitors and manages IP-connected devices.  It is no secret that more devices (or entities) connect to networks by the day, which means the simple network management protocol is becoming increasingly important. 

The protocol is extremely important because it helps Managed Service Providers and network administrators extract the information they need from devices for monitoring and managing them. 

In SNMP, there is a manager-agent relationship that runs the system. The manager is responsible for sending requests to the agents while the agents wait to get a request from the manager to tell them what to do and also reply to the manager with a response.

Find more information about what SNMP is and how SNMP works on our blog. 

In network monitoring and management, SNMP extracts variables and their respective variables about devices. Furthermore, it can offer more granular details about device attributes and behavior. For example, you can use SNMP to monitor variables about almost any device, such as routers, printers, access points, hubs, NAS, UPS, etc. 

Here’s a snapshot of some of the more granular information you can monitor on a device using a simple network management protocol in comparison to standard network monitoring protocols. 

– Hard disk table: Hard Disks, Description, Status, Capacity, Info, Temperature, and Model: 

– Volumes tables: Volumes, Description, Free Size, Total Size, Filesystem, and Status. 

– Basic information: CPU Usage, CPU Temperature, Total Available Memory, Free Memory, Uptime, System Temperature, Number of Hard disks, Volumes, and Last Error Message.

  • Printers: Supply Units (Toner Cartridge, Drum Unit) and Supply Level.

In case you use Domotz network monitoring software, check out our integrations about NAS, UPS and Printers.

Firstly, to start monitoring devices using SNMP, you need access to your device’s OIDs and MIBs. 

In today’s age, network monitoring software like Domotz contains pre-configured SNMP templates. Furthermore, this software will automatically get the OIDs of your devices if they are supported. In addition, this software also enables you to start monitoring your devices immediately without requiring any configuration. 

Alternatively, if your network monitoring software doesn’t already include pre-configured SNMP templates or gather MIB information for you, you can use a MIB browser to find this information.

These are the architecture components of the simple network monitoring protocol:

SNMP Manager

The SNMP manager is the middleman between the human network administrator and the network system that you manage. It ensures the SNMP agents check the value of certain defined variables in the MIB. The manager uses a method called SNMP polling to facilitate this work, and all agents must respond to Polling. You can initiate polling, or do it automatically. Furthermore, in the case of Domotz network monitoring software, the manager is already embedded in Domotz.

SNMP Agent

The agent is in charge of the network communication. It runs on a managed device and is responsible for sending out traps, responding to queries, and answering requests from the SNMP manager. Once the agent receives a request, it acts upon it and sends results to the manager.


Simple network management protocol managers are responsible for managing their SNMP devices. Devices can include firewalls, switches, printers, routers, servers, CCTV cameras, load balancers, and any other device that has SNMP capabilities in their specifications.


In short, commands act to simplify network management. Furthermore, these are the commands that an SNMP Manager can use to inquire about an SNMP Agent.

Here are some examples of basic commands:

GETGet values from the managed device.
GET NEXTGet the next OID Value.
GET BULKRecall bulk data.
TRAPThe trap command is sent by the agent to the manager.
RESPONSEThis is used to carry back the signal of actions directed by the manager.
What is SNMP and what are common commands


MIB is short for Management Information Base. This is a collection of information that is arranged in a hierarchy. All SNMP agents have a database where you can find information about all the devices it manages. MIBs are saved in a text file format. Furthermore, simulation tools, management tools, editors, and everyone who needs the information can understand their formats.


OID is short for Object Identifiers. Their function is to identify objects that are in a MIB hierarchy. There are two types of managed objects:

  • Scalar objects define single objects.
  • Tabular objects define multiple related objects. OIDs are arranged in a hierarchy represented in the form of a tree. Each branch has a number and a name, and the path from the treetop to the point of interest forms the name of that point. Check out more on SNMP OID at our blog.

Community Strings

  • Read-only: With this string, you can only extract read-only information. The function does not let you modify the data; it only reads its values.
  • Read-write: With this string, you can carry out some other functions like reading the data value, modifying these values, and also reset them.
  • Trap community strings: This string receives SNMP traps from the device.

Above all, please note that many devices ship from the factory with a read-only community string set to “public” and read-write community string set to “private”. 

To start, this section covers traps and messages. Firstly, SNMP traps send messages from an agent to a manager. Furthermore, they inform the manager when they detect anomalies at the agent level. In addition, the trap message differs from other messages in the architecture. While other messages have to wait for the manager to send a status request before they can report a situation, the trap message can report itself without request by an instant trigger.

Here are some trap-type messages and their interpretations:

  • Cold Start: When an agent initializes its configuration table.
  • Warm Start: The message interprets an agent re-initializing its configuration table
  • Link Up: This message interprets a network adapter changing its state from down to up.
  • Link Down: Interprets a network adapter changing state from up to down.
  • Authentication Fail: The community name sent by the manager to the agent is invalid.
  • EGP Neighbor loss: The agent cannot communicate with its Exterior Gateway Protocol (EGP).

SNMP has three versions:

  1. V1: The first launch of SNMP v1 was in 1988. Currently, it’s not in use much anymore, which means it is closely becoming obsolete. 
  2. V2c: Firstly, SNMP v2 refers to the most commonly used of the three SNMP v2 versions, SNMP v2c. Additionally, it has an enhanced MIB structure element. 
  3. V3: Security concerns drove the launch of SNMP v3. Furthermore, this version includes more effective features such as authentication and encryption. Ultimately, it focuses more on safety and security to minimize eavesdropping and tampering. Learn more about SNMP v2 vs v3.

Learn all about what is SNMP and how it works, SNMP v2 vs v3, how to find your SNMP OIDs, the differences in the OSI model vs TCP/IP model, and what is a network management tool.

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