MAC address randomization in Ubuntu 17+ (>= 1.4.1): save to /etc/NetworkManager/conf.d/

30-randomize-mac-address.conf

# /etc/NetworkManager/conf.d/30-randomize-mac-address.conf

# REQUIRES NETWORK MANAGER >= 1.4.1 (Ubuntu Zesty and above)

# Thanks to https://blogs.gnome.org/thaller/2016/08/26/mac-address-spoofing-in-networkmanager-1-4-0/

# This randomize your MAC address for *new* connections

# Be sure to change your existing (saved) connections in
# /etc/NetworkManager/system-connections/*

# NOTE: To support captive-portals that rely on a consistent mac address,
#       use `cloned-mac-address=stable` in /etc/NetworkManager/system-connections/[network name]

[device-mac-randomization]
# "yes" is already the default for scanning
wifi.scan-rand-mac-address=yes

[connection-mac-randomization]
ethernet.cloned-mac-address=stable
# wifi.cloned-mac-address=random
# "random" when outside home network
# "stable" when inside home network
wifi.cloned-mac-address=stable
connection.stable-id=${CONNECTION}/${BOOT}

# The options are:
#
# - permanent: use the hardware MAC
# - preserve: don’t change the MAC address of the device upon activation.
# - random: generate a randomized value upon each connect.
# - stable: generate a stable, hashed MAC address.
#

added comments and rules for inside and outside home network