SIMPLE NETWORK MANAGEMENT PROTOCOL
SNMP (Simple Network Management Protocol) is a standard communication protocol used to monitor and manage network devices, computer systems, and various industrial devices.
SNMP allows a central system to monitor device operating status, network connections, CPU and memory utilization, temperature, energy values, fault conditions, and other information provided by the device manufacturer.
SNMP stands for Simple Network Management Protocol. It is a standard communication protocol used to monitor and manage devices and systems within a network.
The primary purpose of SNMP is to collect information about the status of devices and systems and, when required, allow specific management information to be modified. The protocol provides communication between a central management system and an SNMP agent running on a device.
SNMP was originally developed for managing TCP/IP-based networks. Today, it is widely used to monitor switches, routers, firewalls, servers, UPS systems, printers, energy devices, communication equipment, PLCs, RTUs, and various industrial devices.
One of the important features of SNMP is that it allows devices from different manufacturers to be monitored through a standardized management model. The information provided by a device is defined in a MIB (Management Information Base) and addressed using unique identifiers called OIDs (Object Identifiers).
An SNMP architecture basically consists of two main sides: the SNMP Manager and the SNMP Agent.
The SNMP Manager is the central application that monitors devices within a network or industrial system. It can request information from devices, modify supported values, and receive notifications sent by devices.
The SNMP Agent is a software component running on the monitored device that provides access to the device's management information. The agent processes requests received from the Manager and returns the corresponding information.
In simple terms, an SNMP system can be described as: the Manager asks, the Agent responds. In some cases, the Agent can also send a notification to the Manager when an important event occurs.
In the EOS SCADA SNMP client, the data address is specified using the SNMP Object Identifier, or OID. The address starts with the S# prefix.
For example:
The SNMP OID must consist of numerical sections separated by period characters.
The concepts of MIB and OID are fundamental to understanding which information can be accessed from SNMP devices.
MIB (Management Information Base) is a structure containing definitions of the management information provided by an SNMP device. MIB files are used to describe what specific OIDs represent, their data types, and how they are intended to be used.
OID (Object Identifier) is a
hierarchical numerical identifier used to
identify a specific object or piece of information
within SNMP.
For example,
1.3.6.1.2.1.1.3.0
corresponds to a specific SNMP object.
OIDs are organized in a tree structure. Therefore, accessing a data point in SNMP means querying a specific OID, similar in principle to the addressing methods used in SCADA systems.
Manufacturers can also provide device-specific information through their own MIB definitions. Therefore, a manufacturer's MIB file may be required to read information such as temperature, power, fan status, or error codes that are specific to a particular device.
SNMP uses various operation types to read management information, modify supported values, and report events. The most common SNMP operations are described below.
Used to read the current value of a specific OID. For example, device temperature, system uptime, or port status can be retrieved using a GET request.
Used to retrieve the next object in the OID tree. It is particularly useful for traversing tables and objects within a MIB.
Allows multiple management objects to be retrieved more efficiently. It is particularly useful for reading large tables in SNMPv2c and SNMPv3 applications.
Allows authorized users to modify the value of a supported management object on a device. However, which values can be changed depends on the configuration of the device's SNMP agent.
Allows a device to automatically notify an SNMP Manager when an important event occurs. For example, a communication link failure or device restart can be reported using a Trap.
Similar to a Trap, Inform is used to report events. However, unlike a Trap, an Inform message can be acknowledged by the receiver. It can therefore be preferred when a more reliable notification mechanism is required.
Different versions of SNMP have been developed over time. Today, SNMPv2c is widely encountered, while SNMPv3 is preferred when stronger security capabilities are required.
The first widely deployed version of SNMP. It has a simple architecture and supports basic operations such as GET, GETNEXT, SET, and Trap. It can still be found in legacy devices and existing systems.
Provides more advanced protocol operations than SNMPv1. In particular, the GETBULK operation allows large amounts of management information to be retrieved more efficiently.
However, community string-based SNMPv2c does not provide strong security mechanisms.
SNMPv3 introduces more advanced security mechanisms to the SNMP management architecture. It can provide authentication, integrity, and privacy features.
For systems with higher security requirements, SNMPv3 may be a more appropriate choice than SNMPv1 and SNMPv2c.
SNMP applications traditionally use UDP-based communication. UDP 161 is commonly used for requests sent to SNMP Agents, while UDP 162 is used for receiving Traps and similar notifications.
The standard port on which an SNMP Agent listens for normal SNMP requests. Operations such as GET, GETNEXT, GETBULK, and SET can be performed through this port.
The standard port used by an SNMP Manager or Trap Receiver to receive Trap and notification messages.
Therefore, for a SCADA or centralized monitoring application to access SNMP devices, the relevant UDP ports must be reachable through the network and firewall configuration.
SNMP is primarily used for monitoring and managing devices and communication infrastructure rather than as a process control protocol. Nevertheless, it can play an important role as a complementary communication protocol in many industrial facilities.
Switches, routers, firewalls, and other network devices can be monitored for port status, traffic values, error counters, temperature, and similar information.
Voltage, current, load, battery status, operating status, and alarm information can be obtained from UPS systems, power supplies, and certain energy devices.
Operating status, system resources, network interfaces, and various manufacturer-specific parameters can be monitored on servers and computer systems.
PLCs, RTUs, communication devices, industrial switches, and other field equipment supporting SNMP can be monitored from centralized systems.
Trap or Inform notifications received from devices can be forwarded to SCADA, alarm management, or centralized monitoring systems.
SNMP data collected over time can be archived and used for trend analysis, performance monitoring, and capacity planning.
A SCADA system can use SNMP not only to monitor conventional PLC and RTU data, but also to centrally monitor a wide range of information related to the facility's communication infrastructure and auxiliary systems.
For example, in a power generation facility, a SCADA system can collect process data from PLCs, measurements from energy devices, and communication status information from network switches within the same platform.
This approach can help identify problems in the communication infrastructure at an early stage, even when a device itself appears to be operating normally.
SNMP data can be used within SCADA systems together with trending, alarm management, event logging, and reporting mechanisms. This allows network and device management information to be evaluated alongside other operational data of the facility.
A standard management protocol supported by a wide range of network and industrial devices.
Makes it easier to monitor large numbers of devices from different manufacturers through a centralized application.
Its simple protocol structure makes it useful for device management and periodic data collection applications.
Trap and Inform mechanisms allow devices to report important events to centralized systems.
Information collected through SNMP can be archived as time-series data and later used for performance analysis.
SNMPv3 can provide advanced security mechanisms such as authentication, integrity, and privacy.
Although SNMP is a highly useful protocol, it is not by itself suitable as a process communication protocol for every application.
Assume that an SNMP device has the IP address
192.168.1.100.
An SNMP Manager that wants to read a specific OID
from the device can send a GET request for that OID.
For example:
SNMP Agent
IP Address : 192.168.1.100
Port : 161
OID : 1.3.6.1.2.1.1.3.0When the Manager sends a GET request for this OID, the SNMP Agent retrieves the corresponding value and returns it to the Manager in a Response message.
Similarly, when an important event occurs on the device, the Agent can send a Trap to the Trap Receiver of the Manager.
This means that two basic operating models can be used together with SNMP: periodic polling and event-based notification.
This section will provide tools that can be used to test the SNMP protocol, read data from devices, discover OIDs, inspect MIB files, and monitor SNMP Trap messages.
Tools for SNMP Manager and Agent testing, OID querying, MIB viewing, and Trap monitoring will be published here.
Note: This section is currently under development. Free SNMP tools to be developed for the EOS Industrial Software Hub will be published here in the future.
SNMP is a standard communication protocol developed for network and system management and is supported by a very wide range of devices.
Through its MIB and OID structure, management information within devices can be addressed in a standardized manner. GET, GETNEXT, GETBULK, and SET operations can be used to query information or modify supported parameters. Trap and Inform mechanisms allow devices to report events to centralized systems.
Particularly in SCADA and industrial monitoring systems, SNMP is an important complementary protocol that allows network infrastructure, UPS systems, energy devices, communication equipment, and auxiliary systems to be monitored alongside PLC and process data within the same centralized platform.
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