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.

Currently, there are three versions of SNMP defined: SNMP v1, SNMP v2 and SNMP v3. Both versions 1 and 2 have a number of features in common, but SNMPv2 offers enhancements, such as additional protocol operations. SNMP version 3 (SNMPv3) adds security and remote configuration capabilities to the previous versions. To solve the incompatible issues among different versions of SNMP, RFC 3584 defines the coexistence strategies.

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

Protocol Structure

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.

Related Terms: SNMPv1, SNMPv2, SNMPv3, UDP, RMON, SMI, OIDs

Sponsor Source: SNMP is defined by IETF (http://www.ietf.org) through a group of RFCs shown in the reference.

Reference:
http://www.javvin.com/protocol/rfc1155.pdf: Structure and Identification of Management Information for TCP/IP based internets
http://www.javvin.com/protocol/rfc1156.pdf: Management Information Base Network
http://www.javvin.com/protocol/rfc1157.pdf: A Simple Network Management Protocol
http://www.javvin.com/protocol/rfc1441.pdf: Introduction to SNMP v2
http://www.javvin.com/protocol/rfc2579.pdf: Textual Conventions for SNMP v2
http://www.javvin.com/protocol/rfc2580.pdf: Conformance Statements for SNMP v2
http://www.javvin.com/protocol/rfc2578.pdf: Structure of Management Information for SNMP v2
http://www.javvin.com/protocol/rfc3416.pdf: Protocol Operations for SNMP v2
http://www.javvin.com/protocol/rfc3417.pdf: Transport Mappings for SNMP v2
http://www.javvin.com/protocol/rfc3418.pdf: Management Information Base for SNMP v2
http://www.javvin.com/protocol/rfc3410.pdf: Introduction and Applicability Statements for Internet Standard Management Framework
http://www.javvin.com/protocol/rfc3411.pdf: Architecture for Describing SNMP Frameworks
http://www.javvin.com/protocol/rfc3412.pdf: Message Processing and Dispatching for the SNMP
http://www.javvin.com/protocol/rfc3413.pdf: SNMP Applications
http://www.javvin.com/protocol/rfc3414.pdf: User-based Security Model (USM) for SNMP v3
http://www.javvin.com/protocol/rfc3415.pdf: View-based Access Control Model for the SNMP
http://www.javvin.com/protocol/rfc3584.pdf: Coexistence between SNMP v1, v2 and v3