Chapter Goals

Simple Network Management Protocol
Background
SNMP Basic Components
SNMP Basic Commands
SNMP Management Information Base
SNMP and Data Representation
SNMP Version 1

SNMPv1 and Structure of Management Information

SNMPv1 and ASN.1 Data Types
SNMP MIB Tables

SNMPv1 Protocol Operations

SNMP Version 2

SNMPv2 and Structure of Management Information
SMI Information Modules
SNMPv2 Protocol Operations

SNMP Management
SNMP Security
SNMP Interoperability

Proxy Agents
Bilingual Network-Management System

SNMP Reference: SNMPv1 Message Formats

SNMPv1 Message Header
SNMPv1 Protocol Data Unit
Trap PDU Format

SNMP Reference: SNMPv2 Message Format

SNMPv2 Message Header
SNMPv2 Protocol Data Unit

GetBulk PDU Format

Review Questions

Chapter Goals

• Discuss the SNMP Management Information Base.

• Describe SNMP version 1.

• Describe SNMP version 2.

Simple Network Management Protocol

Background

The Simple Network Management Protocol (SNMP) is an application layer protocol that facilitates the exchange of management information between network devices. It is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth.

Two versions of SNMP exist: SNMP version 1 (SNMPv1) and SNMP version 2 (SNMPv2). Both versions have a number of features in common, but SNMPv2 offers enhancements, such as additional protocol operations. Standardization of yet another version of SNMP—SNMP Version 3 (SNMPv3)—is pending. This chapter provides descriptions of the SNMPv1 and SNMPv2 protocol operations. Figure 56-1 illustrates a basic network managed by SNMP.

Figure 56-1: SNMP Facilitates the Exchange of Network Information Between Devices

SNMP Basic Components

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. NMSs provide the bulk of the processing and memory resources required for network management. One or more NMSs must exist on any managed network.

Figure 56-2 illustrates the relationships of these three components.

Figure 56-2: An SNMP-Managed Network Consists of Managed Devices, Agents, and NMSs

SNMP Basic Commands

Managed devices are monitored and controlled using four basic SNMP commands: read, write, trap, and traversal operations.

The read command is used by an NMS to monitor managed devices. The NMS examines different variables that are maintained by managed devices.

The write command is used by an NMS to control managed devices. The NMS changes the values of variables stored within managed devices.

The trap command is used by managed devices to asynchronously report events to the NMS. When certain types of events occur, a managed device sends a trap to the NMS.

Traversal operations are used by the NMS to determine which variables a managed device supports and to sequentially gather information in variable tables, such as a routing table.

SNMP Management Information Base

A Management Information Base (MIB) is a collection of information that is organized hierarchically. MIBs are accessed using a network-management protocol such as SNMP. They are comprised of managed objects and are identified by object identifiers.

A managed object (sometimes called a MIB object, an object, or a MIB) is one of any number of specific characteristics of a managed device. Managed objects are comprised of one or more object instances, which are essentially variables.

Two types of managed objects exist: scalar and tabular. Scalar objects define a single object instance. Tabular objects define multiple related object instances that are grouped in MIB tables.

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