Small changes have been made in three areas:
Various hardware-specific ethernet drivers.
The generic ethernet device driver.
The OpenBSD TCP/IP networking package.
These changes were made in order to export information about the driver and the network that the SNMP agent must report. The changes were trivial in the case of the network stack, since it was already SNMP-friendly. The generic ethernet device driver was re-organized to have an extensive header file and to add a couple of APIs to extract statistics that the hardware-specific device drivers keep within themselves.
There may be a performance hit for recording that data; disabling a config option named something like CYGDBG_DEVS_ETH_xxxx_xxxx_KEEP_STATISTICS depending on the specific device driver will prevent that.
Not all platform ethernet device drivers export complete SNMP statistical information; if the exported information is missing, SNMP will report zero values for such data (in the dot3 MIB).
The interface chipset has an ID which is an OID; not all the latest greatest devices are listed in the available database, so new chipsets may need to be added to the client MIB, if not defined in those from UCD.