NetworkManager dispatcher script to add certain domains for a VPN device when using systemd-resolved (place in /etc/NetworkManager/dispatcher.d, make it executable and adapt VPN domains and connection name)

vpn-domains.sh

#!/bin/bash

set -ex

# ----------------------------------------------------------------------------
# Configuration:

case "$CONNECTION_ID"
in
    "Some VPN name") # enter name of VPN connection in NetworkManager here
        DOMAINS=( # enter domains that should be routed over the VPN here
            some-domain.com
            another-domain.net
        )
        ;;

    # repeat for more VPN connections

    *)
        exit 0
        ;;
esac

# ----------------------------------------------------------------------------

DBUS_PATH="/org/freedesktop/resolve1"
DBUS_IF="org.freedesktop.resolve1"

INTERFACE="$1"
IF_INDEX="$(cat "/sys/class/net/$INTERFACE/ifindex")"

if [[ $2 != "vpn-up" ]]
then
    exit 0
fi

DOMAIN_STR=""
FIRST=true
for DOMAIN in ${DOMAINS[@]}
do
    if [[ $FIRST == true ]]
    then
        FIRST=false
    else
        DOMAIN_STR="${DOMAIN_STR}, "
    fi
    DOMAIN_STR="${DOMAIN_STR}('${DOMAIN}', true)"
done

gdbus call --system --dest $DBUS_IF --object-path $DBUS_PATH --method $DBUS_IF.Manager.SetLinkDomains $IF_INDEX "[$DOMAIN_STR]"