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SNMP

Updated on Jul 8, 2024 by
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What Is SNMP?

SNMP (Simple Network Management Protocol) is a widely-used standard network management protocol for TCP/IP networks. It is employed in network management systems to monitor exceptions on devices connected to the network. SNMP operates through a polling mechanism and provides a basic set of functions, making it suitable for small-scale networks that prioritize speed and cost-efficiency. SNMP messages are transmitted in User Datagram Protocol (UDP) packets, which are compatible with most network devices.

SNMP contains three versions: SNMPv1, SNMPv2c, and SNMPv3, which provide a standardized framework and common language for monitoring and managing devices in the network. SNMP-enabled devices are network switches, routers, printers, etc., these devices are produced by different vendors, the management interface (such as CLI) varies greatly, making network management has become very complex, SNMP is designed to solve this problem and produced, it provides a unified interface, you can different vendors of different devices for unified management, greatly simplifying the network management.

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Key Components of SNMP

The SNMP management model consists of four primary components: the NMS (Network Management System), the SNMP agent, the MIB (Management Information Base), and managed objects. Each managed device features agent access, an MIB, and several management objects.

NMS

The NMS is a network manager that uses SNMP to monitor and control network devices. The NMS software runs on NMS servers to implement the following functions:

  • Send requests to agents on managed devices to query or modify variables.

  • Receive traps from agents on managed devices to learn the device status.

Agent

An agent is a process running on a managed device. It maintains data on the device, responds to requests from the NMS, and reports management data back to the NMS.

  • When the agent receives a request from the NMS, it performs the required operation on the MIB and sends the result back to the NMS.

  • If a fault or event occurs on the managed device, the agent notifies the NMS by sending a message with the current device status.

MIB

A MIB holds the variables maintained by the managed device, which can be queried or modified by the agent. It defines the attributes of the managed device, such as its name, status, access rights, and data type. Using the MIB, an agent can:

  • Determine the current device status.

  • Configure the device status.

Managed Object

A management object is an entity that needs to be managed, which can be a hardware component (such as an interface board) or configuration parameters for hardware or software (such as a routing protocol). The NMS communicates with the agent on a managed device. When the NMS issues a command, the agent executes operations on the MIB within the managed device.

Why Do We Need SNMP?

With the rapid expansion of networks and the increasing diversity of applications, network administrators encounter several challenges:

  • The proliferation of network devices imposes a heavier workload on administrators, compounded by the ongoing expansion of network coverage areas, which complicates real-time monitoring and fault identification.

  • Moreover, the multitude of device types and disparate management interfaces from various vendors add complexity to network management.

SNMP was developed to tackle these challenges. It serves as a standard network management protocol extensively utilized across TCP/IP networks. Integrated within a network management system, SNMP facilitates the monitoring of potential exceptions occurring on network-connected devices. It delivers several advantages:

  • Enhanced operational efficiency: Through SNMP, network administrators gain the ability to retrieve, modify, and identify faults on any device efficiently.

  • Cost-effective management: SNMP offers a foundational toolkit for managing devices with diverse tasks, physical attributes, and network configurations, thus minimizing management expenditures.

  • Reduced impact of configuration operations: The simplicity of SNMP in terms of hardware/software deployment, packet structure, and format mitigates the disruptions caused by feature configuration activities on devices.

How SNMP Works?

SNMPv2c is utilized to illustrate the fundamental workings of SNMP. It executes various operations to fetch data, adjust SNMP object variables, and issue notifications. It's important to note that SNMPv1 lacks support for GetBulk and Inform operations.

Get
It’s a request sent by the NMS to the managed device. And it’s performed to retrieve one or more values from the MIB.
GetNext
It’s similar to the GET. But it usually retrieves the value of the next OID (Object Identifier) in the MIB tree.
GetBulk
It’s used to retrieve a mass of data from large MIB table.
Set
It’s performed by the NMS to modify the value of the managed device.
Response
It’s performed by the agent in response to the GetRequest, GetNextRequest, GetBulkRequest and SetRequest operations.
Trap
This operation is initiated by the agent. It’s used to notify the NMS of a fault or event occurring on a managed device.
Inform
This operation is initiated by the agent. It’s similar to the TRAP, but after the agent sends an inform request, the NMS must send an InformResponse packet as a response to the agent.
 

When the NMS forwards a Get/GetNext/GetBulk/Set request packet to the agent, the agent initially verifies the SNMP version and community name. Upon successful authentication, the agent responds to the NMS with the corresponding value in a response packet. In case the agent encounters difficulty retrieving the corresponding value, it sends an error message to the NMS. It's important to note that the GetBulk operation is equivalent to a sequence of GetNext operations. Users have the option to specify the number of GetNext operations included in a single GetBulk operation, eliminating the need for repeated GetNext operations.

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Trap and Inform represent spontaneous actions performed by the managed device. In the event of a trap-triggering condition, the managed device promptly transmits a trap to the NMS for notification. While similar to a Trap, an Inform necessitates confirmation from the NMS, unlike a Trap which does not require this confirmation. If the managed device fails to receive confirmation, it stores the Inform in the buffer or retries the Inform operation until confirmation is received from the NMS. Upon reaching the maximum limit of retries, the managed device will log the Inform request.

How to Configure SNMP?

SNMP uses a central computer with SNMP software installed to manage network switches. SNMP configuration is not that complicated as most network switches on the market nowadays, be they Gigabit switch or 40G switch, all support SNMP that provides a unified and easy way to manage those switches. Take SNMPv2c configuration as an example. The process includes:

  • Configure IP address on the computer and the managed switches.

  • Enable SNMP.

  • Configure the access rights to enable the computer to manage the specified switches.

  • Verify the configuration result.

The Application Scenarios of SNMP

The NMS facilitates device management via SNMP. Illustrated in the diagram, the network administrator is tasked with configuring and overseeing all devices. However, due to their scattered locations across the site, it becomes impractical for the network administrator to handle each one individually. Furthermore, the devices originate from diverse vendors and offer varying management interfaces, adding complexity to network management. To mitigate operational expenses and enhance productivity, SNMP enables the network administrator to remotely configure and supervise network devices, ensuring real-time monitoring capabilities.

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For network SNMP configuration, set up SNMP Network Management System (NMS) on the management device and SNMP agents on every managed device.

SNMP facilitates:

The NMS to retrieve device information from the SNMP agent on any managed device, enabling remote management and monitoring.

Each agent to promptly relay device status updates to the NMS in real-time.

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