Simulating packet loss with iptables/ipfw

LICENSE

The MIT License (MIT)

Copyright (c) 2010 Richard Cook

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

simulate-packet-loss.sh

#!/bin/bash

IPTABLES_SAVE_FILE_NAME=/tmp/udp-client-server-iptables.save
PLATFORM=`uname -s`
PACKET_LOSS_RATE=$1

# BEGIN: Platform-specific.

function check_preconditions {
  case $PLATFORM in
  Linux)
    if [ -f $IPTABLES_SAVE_FILE_NAME ]
    then
      echo "iptables backup file already exists. Please clean up and try again."
      return 1
    fi
    ;;
  Darwin)
    ;;
  *)
    echo "Unsupported platform \"$PLATFORM\"."
    return 1
    ;;
  esac
}

function set_up {
  case $PLATFORM in
  Linux)
    iptables-save -c > $IPTABLES_SAVE_FILE_NAME
    iptables -A INPUT -m statistic --mode random --probability $PACKET_LOSS_RATE -j DROP
    ;;
  Darwin)
    ipfw add pipe 1 in proto udp
    ipfw pipe 1 config plr $PACKET_LOSS_RATE
    ;;
  *)
    echo "Unsupported platform \"$PLATFORM\"."
    return 1
    ;;
  esac
}

function tear_down {
  case $PLATFORM in
  Linux)
    if [ -f $IPTABLES_SAVE_FILE_NAME ]
    then
      iptables-restore -c < $IPTABLES_SAVE_FILE_NAME
      rm $IPTABLES_SAVE_FILE_NAME
    fi
    ;;
  Darwin)
    ipfw -q flush
    ;;
  *)
    echo "Unsupported platform \"$PLATFORM\"."
    return 1
    ;;
  esac
}

function display_diagnostics {
  echo "--------------------"
  case $PLATFORM in
  Linux)
    iptables --list
    ;;
  Darwin)
    ipfw list
    ;;
  *)
    echo "Unsupported platform \"$PLATFORM\"."
    return 1
    ;;
  esac
  echo "--------------------"
}

# END: Platform-specific.

if [[ `whoami` != "root" ]]
then
  echo "Please run this script as root or using sudo."
  exit 1
fi

if [[ "$PACKET_LOSS_RATE" == "" ]]
then
  echo "Please specify packet loss rate (in range 0.0 to 1.0)."
  exit 1
fi

function on_exit {
  tear_down
  exit $?
}
trap on_exit EXIT

check_preconditions
if [ $? != 0 ]
then
  exit 1
fi

set_up
if [ $? != 0 ]
then
  exit 1
fi

display_diagnostics
if [ $? != 0 ]
then
  exit 1
fi

while [ true ]
do
  echo -n "Press Q to quit and restore firewall settings >"
  read text
  if [[ "$text" == "Q" || "$text" == "q" ]]
  then
    break
  fi
done

tear_down
if [ $? != 0 ]
then
  exit 1
fi