In a local area network switch, a first mode of operation is selected wherein frames are examined for errors as the frames are passed from a source port to a destination port. The LAN switch calculates an error rate as a function of a percentage of the frames passing through the local area network switch which have errors. In response to the error rate exceeding a high error rate threshold, the operating mode is switched to a second mode wherein the entire frame is buffered and examined for errors before the frame is passed from the source port to the destination port. Thereafter, the operating mode may be returned to the first mode if the error rate falls below a low error rate threshold. The local area network switch may also change operating modes as a function of a trend, which indicates a rate of increase or decrease of the error rate.