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Interface Errors and Discards

Elevated interface error rates usually indicate a problem with the transmission medium. For example, the cable, fiber, or interface hardware can cause errors. Each error indicates that the associated packet was dropped during the attempt to transmit or receive it.

When detected in the inbound direction, errors typically indicate problems with the transmission medium (for example, cable or fiber). Outbound errors indicate problems with the interface hardware. The acceptable rate of errors for any given interface is typically zero (0) errors.

Interface discards typically occur when interface buffers no longer have the capacity to store packets (because, for example, buffer memory is exhausted). Buffer congestion often indicates that the rate at which packets are arriving at the interface exceeds its transmission rate.

Each reported discard is a packet that the reporting interface threw out. The sending host must retransmit such packets if a reliable protocol such as TCP is used to send the data end-to-end. Interface discards are typically the result of congested queues serving the interface. Discards frequently occur in bursts. Elevated discard rates may be the result of either microcongestion or chronic congestion issues.

Acceptable discard rates depend on the applications being served, the transmission protocols, and the SLAs established within your organization. Views of interface error and discard totals use a "k" to indicate thousands. Units labeled 'kErrors' or 'kDiscards' therefore refer to thousands of packet errors or thousands of packet discards.