5802

Introduction to SNMP: Knowledge Base

What is SNMP?

Simple Network Management Protocol (SNMP) is a standard protocol language that computers use to send commands to each other and report important information.

SNMP's purpose in monitoring and management systems is to provide network devices with a common language for exchanging data. Today, many computer devices support it, enabling them to work together.

The SNMP model is based on the manager/agent network management architecture. The managers collect and process data about devices on the network. The agents are any type of device component connected to the managed devices in the network (in remote monitoring systems, SNMP agents are usually the RTUs).

There are three versions of SNMP: v1, v2c, and v3. SNMPv3 is the most secure version when compared with the older versions.

NetGuardian 216F
An example of a device that supports SNMP is the NetGuardian 216F by DPS Telecom

SNMP Agents

SNMP "agents" are remote devices out in the network. They can be printers, managed switches, alarm remotes, generators, servers, and lots of other things. These agents report problems and receive commands from a central "manager". This is known as the "manager-agent model".

The SNMP agent listens to requests coming from the SNMP manager on the User Datagram Protocol (UDP) port 161.

SNMP Managers

The manager side of the model describes the device, computer or program that builds reports based on status reports sent by the agents. It ensures that devices are still active, because you may not know if a quiet device is offline or simply doesn't have any alarms to report.

A manager may wait for the agent to send data at a regular, pre-set interval, or it may proactively ask for data using a series of five basic messages: TRAP, GET, GET-NEXT, GET-RESPONSE, and SET.

For example, a manager may ask an agent for data with a "get" message, the agent will send back a "get-response". The manager might only need that one piece of data, or it can then send a "get-next" message (and then another, and then another) to request a full status update.

The SNMP manager listens to Trap messages coming from the agent on port UDP 162.

Real SNMP Application Examples

Seeing real devices in real-world examples is incredibly helpful when learning a new protocol like SNMP. Here is a small collection of examples of typical SNMP deployments including legacy integration. The managers and RTUs and specific, but the concepts are universal:

  1. Use the NetGuardian 216 RTU to report via SNMP
    An SNMP manager like Castle Rock requires SNMP traps. An SNMP RTU like the NetGuardian 216 can convert alarm data into traps and send them to your manager.
  2. Set up your Cordell manager to handle RTUs
    Another example of an SNMP manager as the central alarm aggregator for a fleet of RTUs.
  3. Mediate alarm data as SNMP traps
    Several older pieces of equipment must be modernized by converting data to SNMP in this example.
  4. Use Harris NetBoss to monitor SNMP
    NetGuardian RTUs are installed to report to an existing NetBoss manager.
  5. Forward SNMP traps to your SMARTS InCharge manager
    A mid-level master station can be installed as a multi-protocol aggregator, allowing you to use your preferred SNMP manager for the management of alarms from other protocols as well.
  6. Integrate SONET, Badger, and SNMP equipment
    SONET equipment using TL1 (an ASCII text protocol), which is not natively compatible with SNMP. See how an intermediary master station can bridge this gap.
  7. Send SNMP Traps via LAN To Your Fial Manager
    The application features the Remote Alarm Block to monitor your discrete and analog alarms and report those to your FIAL Master Station.
  8. Migrate from Westronics RTU and IRIS Master - Monitor Radio & Fiber TABS via SNMP
    This application features a customized software platform and modified hardware to provide you with a solution best-suited for your networks.
  9. Roadway Traffic System Monitoring via SNMP and Pager Alerts
    This solution takes the form of our central alarm master station: the T/Mon NOC. The T/Mon NOC will provide you a central aggregation point for SNMP based alarm notifications from the Roadway Traffic System.

More about SNMP protocol

SNMP Traps

A SNMP Trap is one of the 5 basic message types used in SNMP protocol (although more types have been added since version 1 of SNMP). What makes an SNMP trap unique from all other message types is the fact that it is the only method that can be directly initiated by an SNMP agent in the field.

All other core SNMP message types are either initiated by the SNMP manager or issued in response to an SNMP manager's message. This is what makes a trap so important and the most common SNMP message in most networks. A trap is an SNMP agent's way of notifying the manager that there is a problem.

MIB Flow Chart
The device being monitored (a generator or other piece of equipment) sends an alarm to the agent. The agent translates the alarm and sends a Trap message to the manager.

MIB

The Management Information Base, or MIB, is an ASCII text file that catalogs SNMP network elements as a list of data objects, similar to a dictionary of the SNMP language. Every object that is referred to in an SNMP message must be listed in the MIB.

When an SNMP device sends a Trap or other message, it identifies each data object in the message with a number string called an object identifier, or OID. The MIB provides a text label called for each OID. The SNMP manager then uses the MIB to decode the OID numbers into a human-readable display.

Solve MIB problems in 5 easy steps.

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