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What is SNMP?

Simple Network Management Protocol monitoring (SNMP monitoring) is used for monitoring and managing data for your network device. SNMP is embedded in network devices such as switches, routers, and servers, which can be accessed with your IP address. Organizations use SNMP to monitor and manage devices in a local area network (LAN) or wide area network (WAN). Most network devices on the market come bundled with SNMP agents. If not, some devices allow network admins to install the agents.

SNMP emerged in the 1980’s when organizations were increasingly growing in size and complexity. SNMP is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) suite as defined by the Internet Engineering Task Force. Today, SNMP is one of the most widely accepted and used protocols for network monitoring.

What are the different versions of SNMP?

Currently, there are three different versions of SNMP that were developed at different times. Each version comes with a new improvement used to adjust to technological advancements:

  1. SNMPv1: This is the first version of the protocol defined. It involves basic functionalities of data polling. This version is the easiest to set up and resides in RFC 1155 and 1177.
  2. SNMPv2: A revised version that includes enhanced protocol packet types, transport mappings, and MIB structure elements. Defined in RFC 1901, 1905 and 1906, the version improved efficient error handling.
  3. SNMPv3: The is the most recent version that supports remote configuration of SNMP entities. SNMPv3 add encryption and authentication, which drastically improves security and privacy making it the most secure version yet. SNMPv3 is defined by RFC 1905, 1906, 2571, 2572, 2574, and 2575.

How does SNMP work?

SNMP works by sending messages called protocol data unites (PDU) to other devices in your network that speak the SNMP language.

A software server component (SNMP Manager) sends commands that requests information from a software client component (SNMP Agent) that runs on a network device. With certain messages, the SNMP agent can also send information to the SNMP manager on its own. From these messages, the network administrators can manage network device activity. An example of typical SNMP communication starts with the SNMP at the application layer. This then moves through the transport layer (UDP) to the internet layer (IP). The communication process ends at the physical layers (10 base T).

What are the three elements of SNMP? 

For a SNMP to be conducted, there are three main components needed throughout the process:

  1. Managed device: network devices such as a PC, router, switch, or server that contains an SNMP agent
  2. Agent: software management module running on the network device used to manage data on the device and responds to requests by the NMS
  3. Network management system (NMS): referred to as the network manager, monitors the network device by sending requests to the agent and receiving messages from the agent

What is MIB and OID?

A MIB, or Management Information Base, is a database storage used to manage network devices. A MIB is a collection of important information called objects (raw data) that are used by the SNMP manager. Each object in a MIB has an OID, or Object Identifier, with a unique identification. An OID provides a different name to identify quantifiable pieces of data.

Examples of SNMP Commands

SNMP tools perform different functions between network devices and management systems. There are various commands that allow the SNMP manager and SNMP agent to communicate:

  • SNMP Trap: This is used to send alerts, such as error messages. This command is sent by the agent to the manager to alert that something needs to be reported. The manager may also proactively request the data from the agent to check to see if the device is functioning properly.
  • SNMP Get Request: This command is most used by the manager to get data. It retrieves one or more values from the devices.
  • SNMP GetNext Request: This command retrieves the next OID value. It is sent by the SNMP manager to obtain the next OID value in the MIB until there is no other value to get.
  • SNMP GetBulk Request: It obtains large amounts of GetNext requests. This command is sent by the SNMP manager to collect several GetNext requests as the system will allow at once.
  • SNMP Set Request: This command modifies or sets the value of a parameter. It is sent by the SNMP manager to alert the agent to update a configuration setting or issue a command.
  • SNMP Inform Request: This is used to confirm a Trap message has been received. This command is sent by the SNMP manager to which they can confirm that they received the Trap message.
  • SNMP Response Request: This sends the values of action back to the SNMP manager. This command is sent by the SNMP agent in response to a request sent by the SNMP manager. For example, the Response to a SetRequest would be the set of new values as a form of confirmation that the request has been completed.

Why are SNMP monitoring tools important?

SNMP monitoring tools are necessary in organizations because of these capabilities:

  • Automatically discovers, monitors, and manages network devices;
  • Monitors key performance metrics at the device and interface level;
  • Obtains complete visibility into the performance of network devices; and
  • Configures threshold limits and generates alerts in case of anomalies.

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