Number of inbound frames dropped because of format errors or because the virtual circuit was not known. Format errors, in this case, are any errors which would prevent the system from recognizing the DLCI and placing the error in the discard category. This is a 32-bit read-only Counter32, so it only ever increases while the Passport is running and rolls back over to 0 once it wraps -- a monitoring system should poll it periodically and alert on the rate of increase (deltas), not on the raw value, since a rising rate is what signals a real, ongoing problem rather than a one-off event.