• ▸ Output hang: The number of hours, minutes, and seconds since the interface was last reset because of a transmission that took too long.

  • ▸ Input drops: The number of frames dropped on the input interface. Typically, this is a result of congestion on the interface.

  • ▸ Output drops: The number of frames dropped on the output interface.

  • ▸ No buffer: The number of input packets dropped due to a lack of available buffer space.

  • ▸ Broadcasts: The number of broadcasts received on the interface. (Note that this is not an error.)

  • ▸ Throttles: The number of times the local interface requested another local interface within the switch to slow down.

  • ▸ Input errors: The total of no buffer, runts, Giants, CRCs, frame, overrun, ignored, and abort errors.

  • ▸ CRC: The failure of the cyclic redundancy check on an input packet. This can be detected thanks to the FCS field in the Ethernet header.

  • ▸ Frame: The number of frames received that did not end on an 8-bit byte boundary.

  • ▸ Overrun: The number of times the receiver hardware was unable to transfer received data to a hardware buffer because the input rate exceeded the receiver’s ability to process the data.

  • ▸ Ignored: The frames dropped because the interface hardware buffers ran low on internal buffer space.

  • ▸ Abort: An illegal sequence of 1 bit was detected in a frame received.

  • ▸ Dribble condition detected: A dribble bit error occurred, indicating that a frame is slightly too long. The frame is still accepted in this case.

  • ▸ Underruns: The number of times the sender has been running faster than the switch can handle.

  • ▸ Interface resets: The number of times the interface was reset. This is normally the result of missed keepalives from a neighboring device.

  • ▸ Alignment errors: Misaligned reads and writes.

  • ▸ Babbles: The number of transmitted frames greater than 1518 bytes in size.

  • ▸ Late collision: A collision detected after transmitting the first 64 bytes of the frame. According to CSMA/CD and the original Ethernet definition, the time needed to transmit 64 bytes is the maximum time required for a collision to be detected at the furthest interface and a “jamming detected” signal to propagate back to the sender. Under normal conditions, no collision should occur after 64 bytes have been transmitted. If it does, then something is quite wrong. In modern networks, this indicates a manual duplex mismatch (which on Cisco devices would by default be detected by CDP). In older networks, it meant a noncompliant Ethernet implementation or a host being connected on a segment physically longer than the maximum allowed distance.

  • ▸ Deferred: The number of frames transmitted successfully after waiting because the media was busy.

  • ▸ Lost carrier: The number of times the carrier was lost during transmission.

  • ▸ No carrier: The number of times the carrier was not present during the transmission.

  • ▸ Output buffer failures: The number of times a frame was not output from the output hold queue because of a shortage of shared memory.

  • ▸ Output buffers swapped out: The number of frames stored in main memory when the output queue is full.

If counters in the output related to FCS, CRC, alignment, or runts are incrementing, check for a duplex mismatch on the device. Duplex mismatch is a situation where the switch is operating at full-duplex and the connected device is operating at half-duplex or vice versa. A duplex mismatch results in extremely slow performance, intermittent connectivity, and loss of connection. Tracking down duplex mismatches can be tough because a variety of symptoms are possible. Note that some problems, such as slow performance, could also be caused by other issues.