Simulate a lossy network connection

simulate-bad-connection.sh

#!/usr/bin/env bash

[ "$(id -u)" != "0" ] && echo "Please run as root" && exit 1

function usage {
  echo "Usage:
          ./simulate_bad_connection.sh (-a | --address) <dest-ip-address>
                                       [ -d | --delay ] <delay-in-ms>
                                       [ -t | --timeout ] <timeout-seconds>
  "
}

OPTIONS="$(getopt --name simulate_bad_connection --options ha:d:t: --longoptions help,address:,delay:,timeout: -- "$@")"

DELAY=400 # ms
TIMEOUT=300 # seconds

if [ $? != 0 ]; then
    # Incorrect options provided
    usage
    exit 1
fi

eval set -- "$OPTIONS"
while true; do
  case "$1" in
  -h | --help)
    echo "Simulate a bad connection with tc and netem"
    usage
    exit
    ;;
  -a | --address)
    shift
    DEST_ADDRESS="$1"
    ;;
  -d | --delay)
    shift
    DELAY="$1"
    ;;
  -t | --timeout)
    shift
    TIMEOUT="$1"
    ;;
  --)
    shift
    break
    ;;
  esac
  shift
done


if [ -z "$DEST_ADDRESS" ]; then
  echo "Please provide a destination address"
  usage
  exit 1
fi

NETWORK_INTERFACE="$(arp | grep $DEST_ADDRESS | awk '{ print $5 }')"

if [ -z "$NETWORK_INTERFACE" ]; then
  echo "Could not find network interface for address: $DEST_ADDRESS"
  exit 1
fi

# This restores the network
function finish {
  echo "
Restoring network on interface: $NETWORK_INTERFACE"

  # Restore outgoing traffic
  tc qdisc delete dev $NETWORK_INTERFACE root netem &> /dev/null

  # Restore incoming traffic
  tc qdisc delete dev ifb0 root netem &> /dev/null
  tc qdisc delete dev $NETWORK_INTERFACE ingress &> /dev/null
  ip link set dev ifb0 down &> /dev/null
}
# This makes it run when the script exits, no matter how
trap finish EXIT

echo "Simulating bad connection on interface: $NETWORK_INTERFACE"

# Filter outgoing traffic
tc qdisc add dev $NETWORK_INTERFACE root netem \
  delay ${DELAY}ms 20ms distribution normal \
  loss 0.5% 25% \
  corrupt 0.1% \
  reorder 25% 50%

# Filter incoming traffic
# https://wiki.linuxfoundation.org/networking/netem#how_can_i_use_netem_on_incoming_traffic
modprobe ifb
ip link set dev ifb0 up
tc qdisc add dev $NETWORK_INTERFACE ingress
tc filter add dev $NETWORK_INTERFACE parent ffff: protocol ip u32 match u32 0 0 flowid 1:1 action mirred egress redirect dev ifb0

tc qdisc add dev ifb0 root netem \
  delay ${DELAY}ms 20ms distribution normal \
  loss 0.5% 25% \
  corrupt 0.1% \
  reorder 25% 50%

# Wait

echo "Network will restore in $TIMEOUT seconds, or when this script exits"
sleep $TIMEOUT

# finish will be called here