This read-only INTEGER reports the card index on which this interface resides, relative to the bus, with a value of 0 meaning the interface is native to the adapter itself rather than a separate daughter card. An admin tracing a faulty interface back to physical hardware would use this to know whether to inspect the adapter board directly or a specific plugged-in card. For example, a non-zero cnt2SysIfCardIndex tells the admin the interface lives on an add-in card, not the base adapter.