Simple Network Management Protocol

Each Internet Protocol (IP) addressable system in a network, such as a node or a router, hosts a master agent for that system. A master agent typically limits its activity to parsing and to formatting of the protocol.

If the system has multiple manageable subsystems present, the master agent passes on the requests it receives to one or more subagents. These subagents model objects of interest within a subsystem and interface to that subsystem for monitoring and management operations.
The role of the master agent and subagent can merge, in which case one can simply speak of an agent.

A clean separation of the protocol from the structure of management information has made it easy to use SNMP to monitor and often manage hundreds of different subsystems within a network. Within the SNMP architecture, a management information base (MIB) models each managed subsystem with a subsystem-specific definition. This MIB specifies precisely the management data and operations that a subagent makes possible. This model permits management across all layers of the OSI reference model and extending into applications such as databases, email, and the J2EE reference model.

The manager or management station provides the third component. It functions as the equivalent of a client in a client-server architecture. It issues requests for management operations on behalf of an administrator or application, and receives trapss from agents as well.

The SNMP protocol operates at the application layer (layer 7) of the OSI model. It specified (in version 1) five core protocol data units (PDUs):

Other PDUs were added in later versions, including:

Typically, SNMP uses UDP ports 161 for the agent and 162 for the manager.

Development and Usage

Version 1

Version 1 has been criticized for its poor security. Authentication of clients is performed only by a "community string", in effect a type of password, which is transmitted in cleartext.

Version 2

Simple Network Management Protocol version 2 (RFC 1441-RFC 1452), also known as SNMP v2 or SNMP v2p, revises version 1 and includes improvements in the areas of performance, security, confidentiality, and manager-to-manager communications. It introduced GETBULK, an alternative to iterative GETNEXTs for retrieving large amounts of management data in a single request. However, the new party-based security system in SNMP v2, viewed by many as overly complex, was not widely accepted.

Community-Based Simple Network Management Protocol version 2, or SNMP v2c, is defined in RFC 1901-RFC 1908. In its initial stages, this was also informally known as SNMP v1.5. SNMP v2c comprises SNMP v2 without the controversial new SNMP v2 security model, using instead the simple community-based security scheme of SNMP v1. While officially only a "Draft Standard", this is widely considered the de facto SNMP v2 standard.

User-Based Simple Network Management Protocol version 2, or SNMP v2u, is defined in RFC 1909-RFC 1910. This is a compromise that attempts to offer greater security than SNMP v1, but without incurring the high complexity of SNMP v2. A variant of this was commercialized as SNMP v2*, and the mechanism was eventually adopted as one of two security frameworks in SNMP v3.

Version 3

In practice, SNMP implementations often support multiple versions: typically SNMPv1, SNMPv2c, and SNMPv3. See RFC 3584 "Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework".

Usage Example

snmpwalk -c public punch system
SNMPv2-MIB::sysDescr.0 = STRING: Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IO3-M), Version 12.2(15)T5, RELEASE SOFTWARE (fc1)

TAC Support: http://www.cisco.com/tac

Copyright (c) 1986-2003 by cisco Systems, Inc.

Compiled Thu 12-Jun-03 15:49 by eaarm

SNMPv2-MIB::sysObjectID.0 = OID: SNMPv2-SMI::enterprises.9.1.187

DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (835747999) 96 days, 17:31:19.99

SNMPv2-MIB::sysContact.0 = STRING: wikiuser

SNMPv2-MIB::sysName.0 = STRING: punch

SNMPv2-MIB::sysLocation.0 = STRING: test

SNMPv2-MIB::sysServices.0 = INTEGER: 78

SNMPv2-MIB::sysORLastChange.0 = Timeticks: (0) 0:00:00.00


See also

External links