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What is Simple Network Management Protocol?


The SNMP(Simple Network Management Protocol)is a protocol that allows devices to expose useful information to other devices or applications. Using SNMP, the Network operators can be able to manage their network elements, identify the fault, and can configure the remote system.

The SNMP Protocol is based on the communication between an Agent and a Manager.

SNMP Manager:

A manager or management system is a separate entity that is responsible for communicating with the SNMP agent implemented network devices.

SNMP Manager’s key functions
  • Queries agents. 
  • Gets responses from agents Sets variables in agents. 
  • Acknowledges asynchronous events from agents. 
SNMP Agent:

The agent is a program that is packaged within the network element. Enabling the agent allows it to collect the management information database from the device locally and makes it available to the SNMP manager when it is queried for. These agents could be standard (e.g. Net-SNMP) or specific to a vendor (e.g. HP insight agent)

SNMP agent’s key functions
  • Collects management information about its local environment.
  • Stores and retrieves management information as defined in the MIB. 
  • Signals an event to the manager. 
  • Acts as a proxy for some non–SNMP manageable network node.
SNMP Operations:
  • Get Request
    • Get Request is a Read operation on the Managed Device.
    • Get request is used to fetch information from the Managed Device for a particular Object Identifier (OID)
  • Get Next Request
    • Get Next Request is same as Get Request operation. It is used to retrieve the value of the next OID value in the MIB hierarchy.
    • Get Next Request is useful to retrieve more than one piece of information from the Managed Device.
  • Get Bulk
    • Get Bulk Request is used to retrieve a large amount of data from the MIB objects.
    • It internally uses series of Get Next operation to retrieve all data from the MIB tables.
  • Set Request
    • Set Request is a Write operation on the Managed Device.
    • Set Request is used to set/write values in the Managed Device. Basically, it is used to configure Network Elements.
  • Trap
    • Trap is a type of Asynchronous Notification propagated from the Managed Device to the Network Management System.
    • Traps are generated from the Network Elements when it experiences some error condition.
  • Inform
    • SNMP Inform is similar to Traps but is more reliable.
    • When an Agent sends a Trap to the Network Management System (Manager), the Manager receives the Trap and no acknowledgment is sent to Agent. By this way, the Agent doesn’t know whether the Trap has been received by Manager or not. Whereas in Inform Request, the Manager upon receiving the Inform Request can acknowledge the Agent with an SNMP Response PDU. By this way, Agent can be able to know whether Inform has reached or not.
If the Agent didn’t receive the Acknowledgement from the Manager, it can resend the Inform Request again.

OIDs and MIBs

Two crucial SNMP concepts are OIDs (Object Identifier) and MIBs (Management Information Base).SNMP works by querying “Objects”. An object is simply something that we can gather information about on a network device. A MIB is like a translator that helps a Management Station to understand SNMP responses obtained from your network devices.

SNMP Versions Supported
  • SNMP – V1
    • SNMPv1 was the first version of SNMP protocol.
    • SNMPv1 security is based on the Community String authentication.
    • List of operations supported in v1 are Get, Get Next, Get Response, Set, Trap.
  • SNMP – V2
    • SNMPv2 is the next evolution of SNMPv1.
    • Apart from the operations defined in SNMPv1, it adds operations like Get Bulk and Informs. Some of the message formats of the above operations were changed in v2.
    • SNMPv2c is the commonly used one. It also uses the same Community String based security.
  • SNMP – V3
    • SNMPv3 is the recent version and has evolved towards Security.
    • It includes the below security models
      • User-based Security Model
        • Used to identify that the message is from the right source.
      • View-based Access Control Model
        • Used to control which User can access the parts of the MIB objects.
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