Heads up: when following this guide, IKEv2/IPsec VPNs will likely be unresponsive for about 60 seconds at boot and wake. Not sure what causes this issue. Please submit a PR if you know how to fix it!

Requirements

Self-hosted virtual private network (VPN) with public IPv4 address
Computer running macOS Mojave or Catalina

Caveats

When copy/pasting commands that start with $, strip out $ as this character is not part of the command
When copy/pasting commands that start with cat << "EOF", select all lines at once (from cat << "EOF" to EOF inclusively) as they are part of the same (single) command

Guide

Step 1: enable PF

Open "System Preferences", click "Security & Privacy", then "Firewall" and enable "Turn On Firewall".

Then, click "Firewall Options...", disable all options except "Enable stealth mode".

Step 2: confirm PF is enabled

$ sudo pfctl -s info | grep "Status"
No ALTQ support in kernel
ALTQ related functions disabled
Status: Enabled for 0 days 13:02:35           Debug: Urgent

Status: Enabled

👍

Step 3: backup and override `/etc/pf.conf`

Heads up: software updates will likely restore /etc/pf.conf to default. Remember to check /etc/pf.conf using cat /etc/pf.conf after updates and test kill switch.

sudo cp /etc/pf.conf /etc/pf.conf.backup
cat << "EOF" | sudo tee /etc/pf.conf
anchor "local.pf"
load anchor local.pf from "/etc/pf.anchors/local.pf"
EOF

Step 4: list hardware network interfaces

$ networksetup -listallhardwareports

Hardware Port: Wi-Fi
Device: en0
Ethernet Address: Redacted

Hardware Port: Thunderbolt 1
Device: en1
Ethernet Address: Redacted

Hardware Port: Thunderbolt 2
Device: en2
Ethernet Address: Redacted

Hardware Port: Bluetooth PAN
Device: en3
Ethernet Address: Redacted

Hardware Port: iPhone USB
Device: en4
Ethernet Address: Redacted

Hardware Port: Thunderbolt Ethernet
Device: en5
Ethernet Address: Redacted

Hardware Port: Thunderbolt Bridge
Device: bridge0
Ethernet Address: Redacted

VLAN Configurations
===================

Step 4: find hardware network interface subnet prefix (example bellow is for `Wi-Fi` interface)

$ networksetup -getinfo "Wi-Fi"
DHCP Configuration
IP address: 10.0.1.140
Subnet mask: 255.255.255.0
Router: 10.0.1.1
Client ID:
IPv6: Off
Wi-Fi ID: Redacted

Use following table to find bitmask using subnet mask.

For example, if subnet mask is 255.255.255.0, bitmask is /24 and subnet prefix is 10.0.1.0/24.

Subnet mask	Bitmask
0.0.0.0	/0
128.0.0.0	/1
192.0.0.0	/2
224.0.0.0	/3
240.0.0.0	/4
248.0.0.0	/5
252.0.0.0	/6
254.0.0.0	/7
255.0.0.0	/8
255.128.0.0	/9
255.192.0.0	/10
255.224.0.0	/11
255.240.0.0	/12
255.248.0.0	/13
255.252.0.0	/14
255.254.0.0	/15
255.255.0.0	/16
255.255.128.0	/17
255.255.192.0	/18
255.255.224.0	/19
255.255.240.0	/20
255.255.248.0	/21
255.255.252.0	/22
255.255.254.0	/23
255.255.255.0	/24
255.255.255.128	/25
255.255.255.192	/26
255.255.255.224	/27
255.255.255.240	/28
255.255.255.248	/29
255.255.255.252	/30
255.255.255.254	/31
255.255.255.255	/32

Step 5: set temporary environment variables

KILLSWITCH_HARDWARE_INTERFACES should include all used hardware network interfaces.

KILLSWITCH_VPN_INTERFACE should be set to VPN interface (use ifconfig to find interface).

KILLSWITCH_TRUSTED_SUBNET_PREFIXES should include all trusted subnet prefixes such as a home or office subnet prefixes (if trusted).

KILLSWITCH_VPN_ENDPOINT_IPS should include all VPN endpoint IPs.

KILLSWITCH_HARDWARE_INTERFACES="{ en0, en4, en5 }"
KILLSWITCH_TRUSTED_SUBNET_PREFIXES="{ 10.0.1.0/24 }"
KILLSWITCH_VPN_INTERFACE=ipsec0
KILLSWITCH_VPN_ENDPOINT_IPS="{ 185.193.126.203 }"

Step 6: create PF strict anchor

This anchor blocks everything except DHCP and VPN requests.

cat << EOF | sudo tee /etc/pf.anchors/local.pf.strict
# Options
set block-policy drop
set ruleset-optimization basic
set skip on lo0

# Set variables
hardware_interfaces = "$KILLSWITCH_HARDWARE_INTERFACES"
vpn_endpoint_ips = "$KILLSWITCH_VPN_ENDPOINT_IPS"
vpn_interface = "$KILLSWITCH_VPN_INTERFACE"

# Block everything
block all # Use "block log all" to log blocked packets

# Allow DHCP requests (used to establish Wi-Fi connection)
pass on \$hardware_interfaces proto udp from port { 67, 68 } to port { 67, 68 } keep state

# Allow requests to VPN server (used to establish VPN connection)
pass on \$hardware_interfaces proto { tcp, udp } from any to \$vpn_endpoint_ips

# Allow all requests on VPN interface
pass on \$vpn_interface all
EOF
sudo chmod 600 /etc/pf.anchors/local.pf.strict

Step 7: create PF trusted anchor

Same as strict but allows multicast DNS and local network requests.

cat << EOF | sudo tee /etc/pf.anchors/local.pf.trusted
# Options
set block-policy drop
set ruleset-optimization basic
set skip on lo0

# Set variables
hardware_interfaces = "$KILLSWITCH_HARDWARE_INTERFACES"
trusted_subnet_prefixes = "$KILLSWITCH_TRUSTED_SUBNET_PREFIXES"
vpn_endpoint_ips = "$KILLSWITCH_VPN_ENDPOINT_IPS"
vpn_interface = "$KILLSWITCH_VPN_INTERFACE"

# Block everything
block all # Use "block log all" to log blocked packets

# Allow DHCP requests (used to establish Wi-Fi connection)
pass on \$hardware_interfaces proto udp from port { 67, 68 } to port { 67, 68 } keep state

# Allow multicast DNS requests (used to find devices using Bonjour, disable these lines when you don’t trust the network)
pass on \$hardware_interfaces from \$trusted_subnet_prefixes to 255.255.255.255 keep state
pass on \$hardware_interfaces from 255.255.255.255 to \$trusted_subnet_prefixes keep state
pass on \$hardware_interfaces proto udp from \$trusted_subnet_prefixes port 5353 to 224.0.0.251 port 5353 keep state
pass on \$hardware_interfaces proto udp from 224.0.0.251 port 5353 to \$trusted_subnet_prefixes port 5353 keep state

# Allow local network requests (used to access local network, disable this line when you don’t trust the network)
pass on \$hardware_interfaces proto { tcp, udp } from \$trusted_subnet_prefixes to \$trusted_subnet_prefixes

# Allow requests to VPN server (used to establish VPN connection)
pass on \$hardware_interfaces proto { tcp, udp } from any to \$vpn_endpoint_ips

# Allow all requests on VPN interface
pass on \$vpn_interface all
EOF
sudo chmod 600 /etc/pf.anchors/local.pf.trusted

Step 8: create `/etc/pf.anchors/local.pf` symlink

sudo ln -s /etc/pf.anchors/local.pf.strict /etc/pf.anchors/local.pf

Step 9: restart PF

sudo pfctl -F all -f /etc/pf.conf

Step 10: create `/usr/local/sbin` folder

sudo mkdir -p /usr/local/sbin
sudo chown $(whoami):admin /usr/local/sbin/

Step 11: source `/usr/local/sbin` folder

Find which shell is configured using echo $SHELL.

Bash (/bin/bash)

cat << "EOF" >> ~/.bash_profile
export PATH=${PATH}:/usr/local/sbin
EOF
source ~/.bash_profile

Z Shell (/bin/zsh)

cat << "EOF" >> ~/.zshrc
export PATH=${PATH}:/usr/local/sbin
EOF
source ~/.zshrc

Step 12: create `/usr/local/sbin/strict.sh` convenience script

Use socketfilterfw to block specific apps.

cat << "EOF" > /usr/local/sbin/strict.sh
#! /bin/sh

if [ "$(id -u)" != "0" ]; then
  echo "This script must run as root"
  exit 1
fi

green=$'\e[1;32m'
end=$'\e[0m'

# /usr/libexec/ApplicationFirewall/socketfilterfw --blockapp /Applications/1Password\ 7.app
# /usr/libexec/ApplicationFirewall/socketfilterfw --blockapp /usr/local/Cellar/squid/4.8/sbin/squid
# printf "\n"

ln -sfn /etc/pf.anchors/local.pf.strict /etc/pf.anchors/local.pf

pfctl -e

printf "\n"

pfctl -F all -f /etc/pf.conf

printf "\n%s" "${green}Strict mode enabled${end}"
EOF
chmod +x /usr/local/sbin/strict.sh

Step 13: create `/usr/local/sbin/trusted.sh` convenience script

Use socketfilterfw to unblock specific apps (useful to allow 1Password’s local sync or Squid proxy for example).

cat << "EOF" > /usr/local/sbin/trusted.sh
#! /bin/sh

if [ "$(id -u)" != "0" ]; then
  echo "This script must run as root"
  exit 1
fi

red=$'\e[1;31m'
end=$'\e[0m'

function disable()
{
  /usr/local/sbin/strict.sh
  exit 0
}

trap disable EXIT

# /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp /Applications/1Password\ 7.app
# /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp /usr/local/Cellar/squid/4.8/sbin/squid
# printf "\n"

ln -sfn /etc/pf.anchors/local.pf.trusted /etc/pf.anchors/local.pf

pfctl -e

printf "\n"

pfctl -F all -f /etc/pf.conf

printf "\n%s\n\n" "${red}Trusted mode enabled (press ctrl+c to disable)${end}"

while :
do
  sleep 60
done
EOF
chmod +x /usr/local/sbin/trusted.sh

Step 14: create `/usr/local/sbin/disabled.sh` convenience script

cat << "EOF" > /usr/local/sbin/disabled.sh
#! /bin/sh

if [ "$(id -u)" != "0" ]; then
  echo "This script must run as root"
  exit 1
fi

red=$'\e[1;31m'
end=$'\e[0m'

function disable()
{
  /usr/local/sbin/strict.sh
  exit 0
}

trap disable EXIT

pfctl -d

printf "\n%s\n\n" "${red}Firewall disabled (press ctrl+c to enable)${end}"

while :
do
  sleep 60
done
EOF
chmod +x /usr/local/sbin/disabled.sh

Step 15: test convenience scripts

$ sudo strict.sh
Password:
No ALTQ support in kernel
ALTQ related functions disabled
pfctl: pf already enabled

pfctl: Use of -f option, could result in flushing of rules
present in the main ruleset added by the system at startup.
See /etc/pf.conf for further details.

No ALTQ support in kernel
ALTQ related functions disabled
rules cleared
nat cleared
dummynet cleared
0 tables deleted.
64 states cleared
source tracking entries cleared
pf: statistics cleared
pf: interface flags reset

Strict mode enabled

$ sudo trusted.sh
No ALTQ support in kernel
ALTQ related functions disabled
pfctl: pf already enabled

pfctl: Use of -f option, could result in flushing of rules
present in the main ruleset added by the system at startup.
See /etc/pf.conf for further details.

No ALTQ support in kernel
ALTQ related functions disabled
rules cleared
nat cleared
dummynet cleared
0 tables deleted.
6 states cleared
source tracking entries cleared
pf: statistics cleared
pf: interface flags reset

Trusted mode enabled (press ctrl+c to disable)

$ sudo disabled.sh
No ALTQ support in kernel
ALTQ related functions disabled
pf disabled

Firewall disabled (press ctrl+c to enable)

Step 16: make sure PF is set to strict at boot

cat << EOF | sudo tee /Library/LaunchDaemons/local.pf.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>pf</string>

    <key>ProgramArguments</key>
    <array>
      <string>/usr/local/sbin/strict.sh</string>
    </array>

    <key>RunAtLoad</key>
    <true/>
  </dict>
</plist>
EOF

Want things back the way they were before following this guide? No problem!

Step 1: restore `/etc/pf.conf` from backup

sudo cp /etc/pf.conf.backup /etc/pf.conf

Step 2: delete anchors, convenience scripts and launch daemon

Delete anchors

sudo rm /etc/pf.anchors/local.pf
sudo rm /etc/pf.anchors/local.pf.strict
sudo rm /etc/pf.anchors/local.pf.trusted

Delete convenience scripts

rm /usr/local/sbin/strict.sh
rm /usr/local/sbin/trusted.sh
rm /usr/local/sbin/disabled.sh

Delete launch daemon

sudo rm /Library/LaunchDaemons/local.pf.plist

Step 3: restart PF

sudo pfctl -F all -f /etc/pf.conf

README.md Unescape Escape

How to configure self-hosted VPN kill switch using PF firewall on macOS