MIB: EtherLike-MIB
The current mode of operation of the MAC entity. `unknown` indicates that the current duplex mode could not be determined.
Management control of the duplex mode is accomplished through the MAU MIB. When an interface does not support autonegotiation or when autonegotiation is not enabled, the duplex mode is controlled using `ifMauDefaultType`. When autonegotiation is supported and enabled, duplex mode is controlled using `ifMauAutoNegAdvertisedBits`. In either case, the currently operating duplex mode in reflected both in this object and in `ifMauType`.
Note that this object provides redundant information with `ifMauType`. Normally, redundant objects are discouraged. However, in this instance, it allows a management application to determine the duplex status of an interface without having to know every possible value of `ifMauType`. This was felt to be sufficiently valuable to justify the redundancy.
Reference: [IEEE 802.3 Std.], 30.3.1.1.32,aDuplexStatus.