IEEE 802.12 Interface MIB
Extracted elements (20)
32-bit octet counters (dot12InHighPriorityOctets, dot12InNormPriorityOctets, dot12OutHighPriorityOctets) are provided for backward compatibility with SNMPv1 despite rolling over very quickly at 100 Mbps. 64-bit HC variants are the preferred objects for SNMPv2 implementations.
Normal priority receive counters (dot12InNormPriorityFrames, dot12InNormPriorityOctets) are provided because they include errored frames, whereas ifIn*Pkts and ifInOctets do not. This allows calculation of octets in unreadable frames, which is not available elsewhere.
Normal priority transmit counters are not provided because they can be easily calculated: outNormPriorityFrames = ifOutUcastPkts + ifOutMulticastPkts + ifOutBroadcastPkts - dot12OutHighPriorityFrames; standardization was not justified.
An agent should not implement RFC 1643, RFC 1650, or RFC 1748 for IEEE 802.12 interfaces, because those MIBs instrument the ethernet or token ring media access protocols, which 802.12 does not use. IEEE 802.12 uses its own Demand Priority Access Method (DPAM).
When an IEEE 802.12 interface operates in token ring framing mode and the end node supports token ring source routing, the agent should implement RFC 1749 (IEEE 802.5 Station Source Routing MIB) for those interfaces.
All MAC address representations in this MIB module are in canonical order (802.1a, least significant bit first), even when the interface operates in token ring framing mode, which transmits addresses most significant bit first.
An agent implementing this MIB module must support the ifGeneralGroup, ifStackGroup, ifHCPacketGroup, and ifRcvAddressGroup of RFC 1573.
For a master mode interface, dot12DesiredFramingType must be set to frameType88023 or frameType88025; it cannot be frameTypeEither, because a master mode interface cannot grant an unspecified framing type.
Training completion requires that 24 consecutive error-free training frames be received. If fewer are passed, dot12Status transitions to linkFailure; if 24 pass but training configuration bits indicate a problem, the state transitions to openFailure.
dot12Commands is a write-only control object with values noOp(1), open(2), reset(3), close(4). Writing 'open' initiates training (only when closed); 'close' silences the MAC; 'reset' reinitializes MAC and restarts training without affecting MIB counters. Always returns 'noOp' when read.
dot12ControlMode configures master/slave/learn mode for the interface. Interfaces that cannot operate in master mode or use hardware pushbutton control may implement this as read-only. Modifying dot12ControlMode causes the interface to retrain.
dot12LastTrainingConfig is a 2-octet read-only OCTET STRING containing configuration bits from the most recent error-free training frame. On master mode interfaces it holds the requested configuration; on slave mode interfaces it holds the allowed configuration from the training response.
IEEE 802.12 interfaces are identified by ifType value ieee80212(55). The dot12MIB is assigned the OBJECT IDENTIFIER { transmission 45 }, and ifSpecific is set to this value for 802.12 interfaces.
ifMtu for an 802.12 interface depends on the current framing type: 1500 when dot12CurrentFramingType is frameType88023 (Ethernet framing), and 4464 when frameType88025 (Token Ring framing). Changing dot12DesiredFramingType may change ifMtu after the next training.
The dot12StatsGroup includes 14 counters: dot12InHighPriorityFrames/Octets, dot12InNormPriorityFrames/Octets, dot12InIPMErrors, dot12InOversizeFrameErrors, dot12InDataErrors, dot12InNullAddressedFrames, dot12OutHighPriorityFrames/Octets, dot12TransitionIntoTrainings, and 64-bit HC variants for high- and normal-priority octets.
Security issues are not discussed in this memo.
dot12Status defines five states: closed (MAC disabled), opening (training in progress, signals received), opened (training succeeded, 24 error-free frames passed), openFailure (24 frames passed but configuration bits indicate a problem), linkFailure (no training signals or fewer than 24 error-free frames). Transitions are triggered by dot12Commands (open/close/reset), ifAdminStatus, or external events such as MAC protocol violations.
The Allowed Configuration field (2 octets) from the master includes: version bits (vvv), D=duplicate address detected, C=configuration incompatible, N=access denied by security, plus FF/PP/R bits indicating the allowed framing type, promiscuous mode, and node type.
The Requested Configuration field (2 octets) encodes: bits 7-5 of octet 1 = version (vvv, current = 100 binary = 4); bits 3-2 of octet 2 = frame type (FF: 00=88023, 01=88025, 11=Either); bits 1-0 = promisc mode (PP: 00=single, 01=promiscuous); bit 0 of octet 1 side in octet 2 bit-0 = R (0=end node, 1=repeater).
Training frames have the format: DA (6 octets, null destination address), SA (6 octets), Req Config (2 octets), Allow Config (2 octets, zeros in request), Data (594–675 octets), FCS (4 octets). Total minimum size ensures marginal links fail training.