About the Entity MIB

The Entity MIB is defined by the Internet Engineering Task Force RFC 2737 at http://www.ietf.org/rfc/rfc2737.txt. This chapter does not describe the Entity MIB in detail. You should read RFC 2737 before reading this chapter.

The Entity MIB provides a mechanism for presenting hierarchies of physical entities by using SNMP tables. The Entity MIB contains the following groups, which describe the physical elements and logical elements of a managed system:

entityPhysical group

The entityPhysical group describes the identifiable physical resources that are managed by the agent. Resources include the chassis, boards, power supplies, sensors, and so on.

Physical entities are represented by rows in the entPhysicalTable, where one row is provided for each hardware resource. The rows are called entries. A particular row is referred to as an instance. Each table entry has a unique index, entPhysicalIndex, and contains several objects that represent common characteristics of the hardware resource. One object, entPhysicalContainedIn, points to the index of another row in this table. This object is used to indicate whether an entity is contained within another entity. A row for a system board might use entPhysicalContainedIn to specify the index of the row that represents the chassis where the board is installed.

entityLogical group

The entityLogical group describes the logical entities managed by the agent. Logical entities represent nonphysical, abstract elements that provide services. The abstract elements are controlled by higher levels of management. For example, logical entities might represent elements of platform hardware management. Such elements might include functions such as OS reboot, hardware reset, and power control. Logical entities might also represent administrative domains such as Solaris domains or service controllers.

Logical entities are represented as rows in the entLogicalTable, which provides one row for each logical entity. Each table row has a unique index, entLogicalIndex, and contains objects for the logical entity's name, description, and type.

Each row also contains security information that is applicable to SNMPv1, SNMPv2c, and SNMPv3 to allow access to the logical entity's MIB information. If an agent represents multiple logical entities with this MIB, the agent must implement the entityLogical group for all logical entities that are known to the agent. If an agent represents one logical entity, or multiple logical entities within a single naming scope, the agent can omit implementation of this group.

entityMapping group

The entityMapping group describes the objects that represent the associations between elements for which a single agent provides management information. These elements include multiple logical entities, physical components, interfaces, and port identifiers.

The entityMapping group contains the following tables:

• The entPhysicalContainsTable provides a hierarchy of the hardware resources that are represented in the entPhysicalTable. The entPhysicalContainsTable table is two-dimensional, indexed first by the entPhysicalIndex of the containing entry, and second by the entPhysicalChildIndex of the contained entries.

• The entLPMappingTable is the logical-physical mapping table. The entLPMappingTable makes associations between logical entities and physical entities by mapping the indexes of the entLogicalTable to the indexes of entPhysicalTable For example, the table could map a firewall to a particular board.

• The entAliasMappingTable represents mappings of logical entity and physical component to external MIB identifiers.

entityGeneral group

This table describes objects that represent general entity information for which a single agent provides management information. Currently, only one object exists in this group. The object records the time interval between agent startup and the last change to the Physical Entity Table or Physical Mapping Table.

The RFC 2737 and the ENTITY-MIB.txt file describe these tables in more detail. The ENTITY-MIB.txt file is located in the /etc/sma/snmp/mibs directory.