Common Cisco switch port errors

Table of contents

  1. Common network problems
  2. Overview

Common network problems

From my experience the most network problems are on Layer One (Physical layer aka “The cable”). Cisco switches provide a lot of information of the switch interfaces and typically I check:

    swt-3750g#show interfaces counters errors
    swt-3750g#show interfaces status
    swt-3750g#show interfaces GigabitEthernet x/x/x


ErrorPossible cause
Align-ErrMalformed frames, bad hardware, duplex mismatch, half duplex collisions
FCS-ErrBad frame checksum, duplex mismatch, bad hardware
Xmit-Err Speed settings mismatch
Rcv-Err Duplex mismatch, backplane congestion
UnderSizeReceived frames which are less than 64 bytes
OutDiscardsOccur when transmit buffer is full and packets are dropped
Single-ColHalf duplex, duplex mismatch, high utilization of port
Multi-ColHalf duplex, duplex mismatch, high utilization of port
Late-ColCable length, duplex mismatch
Excess-ColSwitch rehad 16 collisions in row, high utilization of port
Carri-SenDuplex settings
RuntsFrame is smaller than 64 bytes and has bad CRC, duplex settings, physical port
GiantsFrame is larger than 1518 bytes and has bad FCS, device source