Definitions of Managed Objects for the Ethernet-like Interface Types
obsoleted by
- rfc-3635 — Definitions of Managed Objects for the Ethernet-like Interface Types
obsoletes
- rfc-2358 — Definitions of Managed Objects for the Ethernet-like Interface Types
Extracted elements (25)
All Ethernet interfaces are recommended to use a single ifType (ethernetCsmacd(6)) regardless of speed, because 'an Ethernet is an Ethernet.' Speed information is available from ifSpeed/ifHighSpeed and MAU type from ifMauType in the MAU-MIB, making separate ifType values for Fast/Gigabit Ethernet unnecessary.
dot3StatsDuplexStatus provides redundant information with ifMauType, which is normally discouraged. The redundancy was judged worthwhile because it allows a management application to determine duplex status without knowing every possible value of ifMauType.
dot3StatsEtherChipSet has been deprecated. Implementation feedback indicated it is more useful in theory than practice: it identifies only the MAC chip (not PHY, PMD, or driver), and the administrative overhead of maintaining a central OID registry cannot be justified for an object of questionable utility.
Several IEEE 802.3 managed objects (aFramesWithExcessiveDeferral, aInRangeLengthErrors, aOutOfRangeLengthField, aMACEnableStatus, aTransmitEnableStatus, aMulticastReceiveStatus, acInitializeMAC) were removed from the MIB based on implementation feedback; others were omitted because the information is derivable from MAU-MIB objects.
Collision-related counters (dot3StatsSingleCollisionFrames, dot3StatsMultipleCollisionFrames, dot3StatsLateCollisions, dot3StatsExcessiveCollisions, dot3StatsDeferredTransmissions, dot3StatsSQETestErrors, dot3StatsCarrierSenseErrors) do not increment when the interface is operating in full-duplex mode, as collisions do not occur in full-duplex operation.
IF-MIB ifInOctets and ifOutOctets include the entire MAC frame (header and FCS), whereas IEEE 802.3 aOctetsReceivedOK and aOctetsTransmittedOK count only clientData and Pad fields. The mapping is: ifInOctets = aOctetsReceivedOK + (18 * aFramesReceivedOK).
IF-MIB ifOut*castPkts count transmit requests from higher layers (including failed ones), while IEEE 802.3 aFramesTransmittedOK counts only successfully transmitted frames. MAC Control frames are not counted by ifOut*castPkts but are counted by aFramesTransmittedOK, and ifOutDiscards/ifOutErrors are counted by ifOut*castPkts but not ifOutOctets.
MAC Control frames are consumed or generated by the interface layer itself and are not counted by ifIn*castPkts or ifOut*castPkts. However, they are included in ifInOctets and ifOutOctets, creating an asymmetry between octet and packet counters in the IF-MIB.
The ifMtu for Ethernet-like interfaces is 1500 octets as seen by the MAC client. When using IEEE 802.2 LLC, higher layers see a different MTU: LLC type 1 clients see 1497 octets and protocols running over SNAP see 1492 octets.
This MIB module is defined using SMIv2. A translation to SMIv1 is possible except that Counter64 objects cannot be translated, so SMIv1-compliant MIBs derived from this document will omit the 64-bit HC counter objects.
64-bit HC octet counters (ifHCInOctets, ifHCOutOctets) are required for Ethernet-like interfaces capable of operating at 20 Mbit/s or faster, even if currently running slower. 64-bit HC packet counters are required for interfaces capable of 640 Mbit/s or faster.
An attempt to set dot3PauseAdminMode to 'enabledXmit(2)' or 'enabledRcv(3)' will fail on interfaces that do not support operation at greater than 100 Mb/s. The value of dot3PauseAdminMode is ignored when the interface is not operating in full-duplex mode.
ifSpeed and ifHighSpeed MUST NOT indicate a doubled value when operating in full-duplex mode; they MUST indicate the correct line speed regardless of the current duplex mode. Before auto-negotiation completes, these objects SHOULD reflect the maximum speed supported by the interface.
It is RECOMMENDED that all Ethernet-like interfaces use an ifType of ethernetCsmacd(6) regardless of speed or link-layer encapsulation. An Ethernet-like interface SHOULD NOT use fastEther(62), fastEtherFX(69), or gigabitEthernet(117) ifTypes.
Standard MIBs do not include objects to return TDR test results; any needed result objects MUST be provided in the vendor-specific MIB. Implementation of the TDR and Loopback tests is not required.
Support for the mauModIfCompl2 compliance statement of the MAU-MIB is REQUIRED for Ethernet-like interfaces, to allow applications to determine the current MAU type, control auto-negotiation, and control duplex mode. Without it there is no standard way to determine media type or control duplex.
dot3CollTable provides a collision histogram indexed by (ifIndex, dot3CollCount), where dot3CollCount ranges 1–16 and dot3CollFrequencies counts MAC frames that experienced exactly that many collisions. This group is optional and does not increment in full-duplex mode.
dot3Compliance is the current MODULE-COMPLIANCE statement, requiring etherStatsBaseGroup as mandatory and conditionally requiring etherDuplexGroup (full-duplex capable), etherStatsLowSpeedGroup (≤10 Mb/s half-duplex), etherStatsHighSpeedGroup (≥100 Mb/s), etherControlGroup, etherControlPauseGroup, and optionally etherCollisionTableGroup.
dot3ControlTable describes the MAC Control sublayer with dot3ControlFunctionsSupported (a BITS object with 'pause(0)' defined) and dot3ControlInUnknownOpcodes (count of MAC Control frames with unsupported opcodes). Only interfaces implementing MAC Control have a row in this table.
dot3PauseTable describes the MAC Control PAUSE function with dot3PauseAdminMode (read-write: disabled/enabledXmit/enabledRcv/enabledXmitAndRcv), dot3PauseOperMode (read-only current mode), dot3InPauseFrames, and dot3OutPauseFrames. Only interfaces supporting the PAUSE function have a row here.
dot3StatsDuplexStatus reports the current MAC operating mode: unknown(1), halfDuplex(2), or fullDuplex(3). Management control of duplex mode is accomplished through the MAU MIB using ifMauDefaultType (when no auto-negotiation) or ifMauAutoNegAdvertisedBits (when auto-negotiation is enabled).
dot3StatsTable provides per-interface Ethernet statistics including alignment errors, FCS errors, single/multiple collision frames, SQE test errors, deferred transmissions, late/excessive collisions, internal MAC transmit/receive errors, carrier sense errors, frame-too-longs, symbol errors, and duplex status. Indexed by dot3StatsIndex (same value as ifIndex).
Two diagnostic test identities are defined: dot3TestTdr (Time-Domain Reflectometry, specific to 10Base5/10Base2, returns a time interval in 10 MHz ticks to the nearest cable fault) and dot3TestLoopBack (internal MAC chip loopback of memory, data paths, and logic; requires the interface to be offline).
The EtherLike-MIB is assigned OID { mib-2 35 } (etherMIB). The dot3 subtree is at { transmission 7 }. The chipset OID tree { dot3 8 } (dot3ChipSets) was previously part of this document but has been moved to a separate document to reduce maintenance overhead.
The read-write object in this MIB is dot3PauseAdminMode, which can be used to configure the PAUSE mode of an interface. Unauthorized modification could disrupt flow control and affect network performance. SNMPv3 with authentication and privacy is recommended to protect management access.