My snmpwalk is gives incorrect output. How can I fix it?

If the switch cannot report the output of

snmpwalk -c public -v1 -On <switch> .1.3.6.1.2.1.17.7.1.2.2.1.2

correctly then the showport command (and port detection in general) will not work out of the box. For example on a Dell S4148f-ON switch, SNMP failed to detect ports properly due to the switch not reporting snmpwalk output correctly.

A workaround for this issue is to create a custom control script in which you write your own logic to extract the MAC addresses from the switch and then MAP them to the correct port:

#!/bin/bash
# Example custom switch control script v1.0"

usage() {
  echo "$0 <command> <args>"
  echo " -h show this help"
  echo " --provides list available commands"
}

if [ -z "$1" -o "$1" == "-h" ]; then
  usage
  exit 1
fi

if [ "$1" == "--provides" ]; then
  echo "portbymac"

if [ "$1" == "portbymac" ]; then # lower case : separated
  if [ "$2" == "00:00:00:00:00:01" ]; then
    echo 1
  elif [ "$2" == "00:00:00:00:00:02" ]; then
    echo 2
  elif [ "$2" == "00:00:00:00:00:03" ]; then
    echo 3
  elif [ "$2" == "00:00:00:00:00:04" -o "$2" == "01:00:00:00:00:04" ]; then
    echo 4
  elif [ "$2" == "00:00:00:00:00:0A" ]; then
    echo 10
  elif [ "$2" == "00:00:00:00:00:0B" ]; then
    echo 11
  elif [ "$2" == "00:00:00:00:00:0C" ]; then
    echo 12
  fi
fi

Inside the "if [ "$1" == "portbymac" ]; " you can add the logic to extract the MAC addresses and MAP them to ports.