SNMP: Simple Network Management Protocol

Simple Network Management Protocol (SNMP) is the protocol developed to manage nodes (servers, workstations, routers, switches and hubs etc.) on an IP network. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth. Network management systems learn of problems by receiving traps or change notices from network devices implementing SNMP.

An SNMP managed network consists of three key components: managed devices, agents, and network-management systems (NMSs). A managed device is a network node that contains an SNMP agent and that resides on a managed network. Managed devices collect and store management information and make this information available to NMSs using SNMP. Managed devices, sometimes called network elements, can be routers and access servers, switches and bridges, hubs, computer hosts, or printers. An agent is a network management software module that resides in a managed device. An agent has local knowledge of management information and translates that information into a form compatible with SNMP. An NMS executes applications that monitor and control managed devices.

The following picture illustrates the SNMP architecture:

Currently, there are three versions of SNMP defined: SNMP v1 , SNMP v2 and SNMP v3 . The following table provides the summary of the operations and features of the different version SNMP:

SNMP v1	Basic Operations and Features
Get	Used by the NMS to retrieve the value of one or more object instances from an agent
GetNext	Used by the NMS to retrieve the value of the next object instance in a table or a list within an agent
Set	Used by the NMS to set the values of object instances within an agent.
Trap	Used by agents to asynchronously inform the NMS of a significant event.
SNMP v2	Additional Operations and Features
GetBulk	Used by the NMS to efficiently retrieve large blocks of data.
Inform	Allows one NMS to send trap information to another NMS and to then receive a response.
SNMP v3	Security Enhancement
	User-based Security Model (USM) for SNMP message security.
	View-based Access Control Model (VACM) for access control.
	Dynamically configure the SNMP agents using SNMP SET commands.

SNMP also includes a group of extensions as defined by RMON, RMON 2 , SMI, OIDs, Enterprise OIDs, etc.

Protocol Structure - SNMP Simple Network Management Protocol

SNMP is an application protocol, which is encapsulated in UDP . The general SNMP message format for all versions is shown below:

• Version -- SNMP version number. Both the manager and agent must use the same version of SNMP. Messages containing different version numbers are discarded without further processing.
• Community -- Community name used for authenticating the manager before allowing access to the agent.
• PDU (Protocol Data Unit) -- The PDU types and formats are different for SNMPv1, v2 and v3, which will be explained in the corresponding sections.