Structure of Management Information

The writing of MIBs is governed by a set of rules known as the Structure of Management Information, (SMI). This set of documents contains industry-accepted methods and rules for specifying the following information:

• The model of management information

• Types of management information

• Types of events

The System Management Agent uses SMIv2. SMIv2 instructs about organization object names so that logical access can occur. SMIv2 states that each managed object must have the following attributes:

A name

The name, an object identifier (OID), uniquely identifies the object. The assignment of an OID value to an object registers that object. For more information, see ISO Namespace Tree.

A syntax

The syntax defines the data type, such as an integer or a string of octets.

An encoding

The encoding describes how the information associated with the managed objects is serialized for transmission between machines.

Community String

In SNMP, one or several managers together with an agent is known as a community. SNMPv1 and v2c messages contain the name of a community, known as a community string. While SNMPv3 packets are associated to users specified in USM settings, SNMPv2 and v1 packets have an associated community string. The community string is an octet string variable used for the following checks:

• Identifying the requesting entity.

• Indicating the location of the requesting entity.

• Determining the MIB view information.

The VACM supported by the SMA elaborates on the community string model with a dynamic access control model. The dynamic access control model for SNMPv3 is explained in Using VACM for Access Control.

The com2sec token maps a community to an SNMPv3 security name, so that the community can use VACM views. For more information, see Chapter 4, Managing Security.