Simple Network Management Protocol (SNMP)

Introduction

• SNMP stands for “Simple Network Management Protocol “.
• It was developed in 1988.

Definition

• It is a standard protocol for internetwork management because it is a simple(small number of commands used for communication, its reliance on connectionless communication link) and requiring little code to implement it, and  also vendors can easily build SNMP agents to their products.

Characteristics

• SNMP protocol is extensible in structure and hence allowing vendors to easily add network management functions to their existing products.
• This protocol is believed to be robust’ because of the independence of the managers from the agents i.e. if an agent fails in its working, the manager will continue to its function, or vice versa.
• SNMP uses different Security levels (such as authentication and authorization).
• The primary protocol used by SNMP is User Datagram Protocol (UDP) and the Internet Protocol (IP) during the processing. 
• SNMP is  based on the Manager/Agent model
• SNMP also separates the management architecture from the architecture of the hardware devices, which broadens the base of multivendor support.

Architecture

• It consisting of a manager, an agent, a database of management information, managed objects and the network protocol.
  • Here, the manager component provides the interface between the human network manager and the management system. A typical manager performs the following functions:-
    • Creates Network Management Station (NMS)
    •  Implements full SNMP Protocol
    • Acts as Query agents
    • Get responses from agents
    • Set’s variables in agents
    • Acknowledge’s asynchronous events from agents.
  • The agent component provides the interface between the manager and the physical device(s) being managed. A typical agent performs the following functions:-
    • Implements full SNMP protocol.
    • Stores and retrieves management data as defined by the Management Information Base.
    • Can asynchronously signal an event to the manager.
    • Can be a proxy for some non-SNMP manageable network node.
  • Management Information Base (MIB):
    • It is a common place where manager and agent exchange their information using small set of commands called Management Information Base (MIB).
    • The MIB is actually organized in a tree structure form with individual variables(such as point status or description) being represented as leaves on the branches.
    • A long numeric tag or object identifier (OID) is used to distinguish each variable uniquely in the MIB and in SNMP messages.

Working Mechanism

• SNMP uses five basic messages commands (GET, GET-NEXT, GET-RESPONSE, SET, and TRAP) to communicate between the manager and the agent in MIB.
• The GET and GETNEXT messages allow the manager to request information for a specific variable. The agent, upon receiving a GET or GET-NEXT message, will issue a GET-RESPONSE message to the manager with either the information requested or an error indication as to why the request cannot be processed.
• A SET message allows the manager to request a change to be made to the value of a specific variable in the case of an alarm remote that will operate a relay. The agent will then respond with a GET-RESPONSE message indicating the change has been made or an error indication as to why the change cannot be made.
• The TRAP message allows the agent to spontaneously inform the manager of an an ‘important’ event.
• The most of the messages (GET, GET-NEXT, and SET) are only issued by the SNMP manager.
• The TRAP message is the only message which is initiated by an agent.

Disadvantages

• SNMP supports connectionless communication i.e. no prearranged communication path is established prior to the transmission of data. As a result, SNMP makes no guarantees about the reliable delivery of the data.
• SNMP does not perform the recovery and error detection function up to the NMS (Network Management Station) and even up to the agent level.

Function/Use

• This protocol helps in Authorization and Authentication process.