Entity MIB using SMIv2
obsoleted by
- rfc-2737 — Entity MIB (Version 2)
Extracted elements (26)
All Entity MIB objects are read-only by conscious working group decision to limit the MIB's scope. The restriction may be lifted after implementation experience by adding writable tables via the AUGMENTS clause, rather than modifying existing objects.
The Entity MIB deliberately does not expose administrative relationships between logical entities or distinguish between locally-realized and proxy-realized MIB instances, because management of the administrative framework was explicitly out of scope pending operational experience.
The Entity MIB is intentionally not a 'Chassis MIB replacement.' A previous IETF working group failed to reach consensus on a Chassis MIB, likely due to overly broad scope. This MIB limits itself to representing logical/physical entity relationships rather than full chassis management.
The entLPMappingTable should include only the most appropriate physical component closest to the root of the containment tree. Redundant mappings derivable from entPhysicalContainedIn should be omitted; per-port mappings are appropriate only when multiple logical entities share the same module's ports.
For community-based SNMP, distinguishing logical entities is one purpose of the community string. Different logical entities may share the same naming scope (entLogicalCommunity value) provided they have no need for the same MIB object instance to represent different managed information.
Multiple agents within the same managed system are free to implement the Entity MIB independently; multiple instances are not required to be equivalent or consistent. An NMS may attempt to align instances by examining table columns, but vendor-specific identifiers and index values are likely to differ across agents.
The Entity MIB is itself a single-scoped MIB. The entLogicalTAddress and entLogicalTDomain objects support a historical multiplexing mechanism and are not intended to identify other SNMP agents; an agent's entLogicalTable is not required to contain information about logical entities managed primarily by other agents.
All MIB objects defined in the Entity MIB have at most read-only MAX-ACCESS; none are writable. A compliant SNMP agent must implement all five mandatory groups: entityPhysicalGroup, entityLogicalGroup, entityMappingGroup, entityGeneralGroup, and entityNotificationsGroup.
An agent must not generate more than one entConfigChange trap-event in a five-second period. If additional configuration changes occur within this throttling window, those trap-events must be suppressed. An NMS should periodically check entLastChangeTime to detect missed traps.
Only entPhysicalIndex values which represent physical ports (entPhysicalClass = port(10)) are permitted to exist in the entAliasMappingTable.
The entLogicalTable must contain at least one entry. The entLogicalCommunity agent must not return a community string which allows more privileges than the community string used to access this object.
The entPhysicalTable must always contain at least one row for an 'overall' physical entity. An agent must represent both empty and full containers in the entPhysicalTable.
The value of entPhysicalContainedIn for a 'module' entity (entPhysicalClass = module(9)) must equal an entPhysicalIndex representing the parent 'container' entity (entPhysicalClass = container(5)). The containment relationships define a strict hierarchy; recursion is not allowed.
entLastChangeTime (entityGeneral group) records the value of sysUpTime at the time any conceptual row is created or deleted in the five Entity MIB tables, or when any of 12 listed object instances change value. It serves as a change-detection timestamp for NMS polling.
The entAliasMappingTable maps (entPhysicalIndex, entAliasLogicalIndexOrZero) pairs to external MIB identifiers (RowPointer). Only physical ports (entPhysicalClass = port(10)) may appear. A zero value for entAliasLogicalIndexOrZero acts as a wildcard, applying to all logical entities without a specific entry; non-zero entries take precedence.
The entConfigChange NOTIFICATION-TYPE is sent when entLastChangeTime changes, enabling an NMS to trigger entity table maintenance polls. An agent must not generate more than one entConfigChange trap-event in a five-second throttling period; additional changes during that window must be suppressed.
The Entity MIB (ENTITY-MIB) is assigned OID { mib-2 47 } and contains five conformance groups: entityPhysical, entityLogical, entityMapping, entityGeneral, and entityNotifications. It represents multiple logical and physical entities managed by a single SNMP agent.
The entLogicalTable contains one row per logical entity, indexed by entLogicalIndex (integer 1..2147483647). Each entry includes entLogicalDescr, entLogicalType, entLogicalCommunity (OCTET STRING 1..255), entLogicalTAddress, and entLogicalTDomain to support SNMPv1/v2C access to the logical entity's MIB information. At least one entry must exist.
The entLPMappingTable maps entLogicalIndex values to entPhysicalIndex values, representing which physical components support each logical entity. A logical entity can map to multiple physical components and vice versa. Agents should limit entries to meaningful, non-redundant associations.
The entPhysicalContainsTable exposes container/containee relationships indexed by (entPhysicalIndex, entPhysicalChildIndex), providing a direct format equivalent to traversing the containment tree via entPhysicalContainedIn. This allows an NMS to quickly discover all children of a given physical entity.
The entPhysicalTable contains one row per physical entity, indexed by entPhysicalIndex (PhysicalIndex, integer 1..2147483647). Each entry includes entPhysicalDescr, entPhysicalVendorType, entPhysicalContainedIn, entPhysicalClass, entPhysicalParentRelPos, and entPhysicalName. The table must always contain at least one row for an 'overall' physical entity.
The PhysicalClass textual convention enumerates hardware types: other(1), unknown(2), chassis(3), backplane(4), container(5), powerSupply(6), fan(7), sensor(8), module(9), port(10). It is used by entPhysicalClass to indicate the general hardware type of a physical entity.
The ENTITY-MIB module is registered under mib-2 47 (OID { mib-2 47 }), assigned by IANA as part of the MIB-II subtree. The module defines the entityMIB MODULE-IDENTITY with LAST-UPDATED '9605160000Z'.
The Entity MIB exposes potentially sensitive management information about logical and physical entities. A network administrator should employ instance-level access control, configuring community strings such that sensitive instances (e.g., entLogicalCommunity, entLogicalEntries, entPhysicalEntries, and mapping table entries) are excluded from particular MIB views.
entLogicalTAddress is formatted according to entLogicalTDomain. For snmpUDPDomain, TAddress is 6 octets: the initial 4 octets contain the IP address in network-byte order, and the last 2 octets contain the UDP port in network-byte order.
entPhysicalParentRelPos is an INTEGER (-1..2147483647) indicating the relative position of a child component among its siblings. The value -1 indicates position cannot be determined or entPhysicalContainedIn is 0; non-negative values reflect parent-relative ordering, normally starting from 1 unless the device labels from 0.