The Network Management Model contains three components:

A Network Management Station is a host that runs network management applications and is responsible for managing the network. For example, a Silicon Graphics workstation running NetVisualyzer Display Station software is a network management station.

Network management applications typically reside in the network management station and collect data from various agents in the network. They process and present that data to the user. The applications may also control or configure the data and thus affect the behavior of the underlying network entity or device. NetVisualyzer tools are examples of network management applications.

An agent is software or firmware that gathers the information important to the device on which it resides. It also implements a protocol that exchanges that information with a network management station. snmpd(1M) is an example of an SNMP agent.

The network management protocol is the protocol used to convey management information between an agent and a network management application. The protocol used by Browser to query information from various agents is SNMP.

SNMP is the network management protocol used by Browser to talk to agents on remote managed nodes. It is defined in RFC 1157 (see “Protocol References” in Appendix C). For Silicon Graphics workstations, the SNMP agent is snmpd(1M). Agents for other types of nodes may be implemented in software or firmware and are vendor-specific.

A managed node is a device such as workstation, router, or hub that has an SNMP agent implemented.

A MIB is the specification for the virtual store of the information supported by an agent. Some MIBs have RFC status, which means they have been approved by the IETF.

MIBs are defined in SMI format. For instance, a router MIB is a collection of important information about a router defined in SMI format. An SNMP agent typically implements two MIBs, MIB-II and a device-specific MIB (an Enterprise MIB). However, the agent may not implement all of the objects defined in each MIB.

The vast information that agents gather about devices is organized into a hierarchical tree called the SNMP Containment Tree. A portion of this tree is shown in Figure E-1. Some of the subtrees in this tree are MIBs. In Figure E-1, mib-2, cisco, and cabletron are MIBs.

Each node with children in the SNMP Containment Tree (Figure E-1) is called a subtree.

MIB-II is the Internet-standard MIB (RFC 1213). This MIB has managed objects that are important for managing the TCP/IP suite of protocols. The subtrees of MIB-II—system, interfaces, at, ip, and so on—and some of their variables are shown in Figure E-2.

A managed object is also known as a variable. Figure E-2 shows an additional portion of the SNMP Containment Tree. In this figure, the managed objects are solid circles. For example, sysContact is an object in mib-2 that contains the name of the contact person for that system.

A leaf node in the SNMP Containment Tree is called a variable. In the SMI definition for each MIB, each variable is defined to be read-write, read-only, or write-only.

An object identifier is a name in a dot notation that uniquely identifies an object (subtree or managed object) in the MIB. It is a sequence of numbers that traverses the SNMP Containment Tree shown partially in Figure E-1. For example, the object ID for sysContact is 1.3.6.1.2.1.1.4.

SMI is a textual format for the schema that is the precise definition of a managed object.

Enterprise MIBs are MIBs defined by different vendors for managing their devices. They can be very device or vendor specific. For example, the CISCO MIB has objects for the Cisco router.

A community string is a password used by an SNMP agent for authentication purposes. The default string for Silicon Graphics workstations is “public”. Community strings are typically defined by system administrators.

A Request for Comment is an Internet standards document for a technology, concept, or protocol.

The Internet Engineering Task Force is a community of network designers, operators, vendors, and researchers whose purpose is to coordinate the operation, management, and evolutions of the Internet, and to resolve short- and mid-range protocol and architectural issues.