Mac OSX simulate poor network conditions

README.md

📡 simulate-network

A simple macOS utility to simulate different network conditions (e.g. 3G, 4G, edge, wifi) for all TCP and UDP traffic. Useful for testing how your app behaves under degraded or limited network environments.

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✅ Features

• Simulate bandwidth throttling, latency, and packet loss
• Affects all TCP and UDP traffic (including WebRTC)
• Easy reset to return to normal
• macOS-native using pfctl and dnctl

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🔧 Requirements

• macOS with pfctl and dnctl (usually built-in)
• Root access (sudo)
• Bash shell (bash >= 3)

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🚀 Usage

# Make the script executable
chmod +x simulate-network

# Simulate a 3G network with 1% packet loss
sudo ./simulate-network 3g --loss 1

# Simulate wifi conditions (default delay and bandwidth)
sudo ./simulate-network wifi

# Reset all simulation and restore normal network behavior
sudo ./simulate-network reset

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🌐 Supported Presets

Speed	Bandwidth	Latency
edge	240 Kbit/s	400 ms
3g	750 Kbit/s	200 ms
4g	4000 Kbit/s	80 ms
wifi	30000 Kbit/s	20 ms

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⚠️ Limitations

• Jitter is not supported on macOS's dnctl (it will be ignored with a warning)
• Only one simulation can be active at a time
• Must be run with sudo

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📁 Files

• simulate-network – the Bash script
• README.md – this file

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🧼 Cleanup

Always run the following to restore your system to a normal state after testing:

sudo ./simulate-network reset

simulate-network

#!/usr/bin/env bash

# -------- Bootstrap: force Bash --------
if [ -z "$BASH_VERSION" ]; then
  exec /usr/bin/env bash "$0" "$@"
fi

set -e

DEFAULT_INTERFACE="en0"
TMP_PF_CONF="/tmp/pf.conf.simnet"

print_usage() {
  echo "Usage: $0 [speed] [--loss %] [--jitter ms]"
  echo "       $0 reset"
  echo ""
  echo "Speeds: edge, 3g, 4g, wifi"
}

require_root() {
  if [ "$EUID" -ne 0 ]; then
    echo "Please run as root (e.g. sudo $0 ...)"
    exit 1
  fi
}

list_interfaces() {
  echo "Available network interfaces:"
  ifconfig | awk '/flags=/{gsub(":", "", $1); iface=$1} /status: /{print " - " iface ": " $2}' \
    | sed "s/^ - $DEFAULT_INTERFACE/ * $DEFAULT_INTERFACE/"
  echo ""
}

reset_network() {
  echo "Resetting network simulation..."
  sudo pfctl -d
  sudo dnctl flush
  echo "✅ Network simulation reset."
  exit 0
}

# -------- Parse Arguments --------
if [ "$1" == "reset" ]; then
  require_root
  reset_network
fi

if [ $# -lt 1 ]; then
  print_usage
  exit 1
fi

SPEED=$1
shift

# Default values
LOSS=0
JITTER=0

while [[ $# -gt 0 ]]; do
  key="$1"
  case $key in
    --loss)
      LOSS="$2"
      shift; shift
      ;;
    --jitter)
      JITTER="$2"
      shift; shift
      ;;
    *)
      echo "Unknown option: $key"
      print_usage
      exit 1
      ;;
  esac
done

# Map speed to bandwidth/delay
case "$SPEED" in
  edge)
    BW=240
    DELAY=400
    ;;
  3g)
    BW=750
    DELAY=200
    ;;
  4g)
    BW=4000
    DELAY=80
    ;;
  wifi)
    BW=30000
    DELAY=20
    ;;
  *)
    echo "Invalid speed: $SPEED"
    print_usage
    exit 1
    ;;
esac

# -------- Apply Network Simulation --------
require_root
list_interfaces

echo "Using interface: $DEFAULT_INTERFACE"
echo "Setting network simulation:"
echo "  Speed: $SPEED ($BW Kbit/s, $DELAY ms)"
echo "  Loss: $LOSS%"

if [ "$JITTER" -gt 0 ]; then
  echo "⚠️  Warning: 'jitter' is not supported by macOS dummynet and will be ignored."
fi

sudo dnctl flush
sudo dnctl pipe 1 config bw ${BW}Kbit/s delay ${DELAY}ms plr $(awk "BEGIN {print $LOSS / 100}")
sudo dnctl pipe 2 config bw ${BW}Kbit/s delay ${DELAY}ms plr $(awk "BEGIN {print $LOSS / 100}")

cat <<EOF > $TMP_PF_CONF
dummynet in quick on $DEFAULT_INTERFACE proto { tcp udp } from any to any pipe 1
dummynet out quick on $DEFAULT_INTERFACE proto { tcp udp } from any to any pipe 2
EOF

sudo pfctl -f $TMP_PF_CONF
sudo pfctl -e

echo "✅ Network simulation applied."