/etc/NetworkManager/NetworkManager.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=False

#######################################################
/etc/NetworkManager/dispatcher.d/01ifupdown

#!/bin/sh -e
# Script to dispatch NetworkManager events
#
# Runs ifupdown scripts when NetworkManager fiddles with interfaces.
# See NetworkManager(8) for further documentation of the dispatcher events.

# We do not handle connectivity-change events in ifupdown so simply exit at
# this point
if [ "$2" = "connectivity-change" ]; then
    exit 0;
fi

if [ -z "$1" ]; then
    echo "$0: called with no interface" 1>&2
    exit 1;
fi

if [ -n "$IP4_NUM_ADDRESSES" ] && [ "$IP4_NUM_ADDRESSES" -gt 0 ]; then
   ADDRESS_FAMILIES="$ADDRESS_FAMILIES inet"
fi
if [ -n "$IP6_NUM_ADDRESSES" ] && [ "$IP6_NUM_ADDRESSES" -gt 0 ]; then
   ADDRESS_FAMILIES="$ADDRESS_FAMILIES inet6"
fi

# If we have a VPN connection ignore the underlying IP address(es)
if [ "$2" = "vpn-up" ] || [ "$2" = "vpn-down" ]; then
   ADDRESS_FAMILIES=""
fi

if [ -n "$VPN_IP4_NUM_ADDRESSES" ] && [ "$VPN_IP4_NUM_ADDRESSES" -gt 0 ]; then
   ADDRESS_FAMILIES="$ADDRESS_FAMILIES inet"
fi
if [ -n "$VPN_IP6_NUM_ADDRESSES" ] && [ "$VPN_IP6_NUM_ADDRESSES" -gt 0 ]; then
   ADDRESS_FAMILIES="$ADDRESS_FAMILIES inet6"
fi

# We're probably bringing the interface down.
[ -n "$ADDRESS_FAMILIES" ] || ADDRESS_FAMILIES="inet"

# Fake ifupdown environment
export IFACE="$1"
export LOGICAL="$1"
export METHOD="NetworkManager"
export VERBOSITY="0"

for i in $ADDRESS_FAMILIES; do

    export ADDRFAM="$i"

    # Run the right scripts
    case "$2" in
        up|vpn-up)
            export MODE="start"
            export PHASE="post-up"
            run-parts /etc/network/if-up.d
            ;;
        down|vpn-down)
            export MODE="stop"
            export PHASE="post-down"
            run-parts /etc/network/if-post-down.d
            ;;
# pre-up/pre-down not implemented. See
# https://bugzilla.gnome.org/show_bug.cgi?id=387832
#        pre-up)
#            export MODE="start"
#            export PHASE="pre-up"
#            run-parts /etc/network/if-pre-up.d
#            ;;
#        pre-down)
#            export MODE="stop"
#            export PHASE="pre-down"
#            run-parts /etc/network/if-down.d
#            ;;
        hostname|dhcp4-change|dhcp6-change)
            # Do nothing
            ;;
        *)
            echo "$0: called with unknown action \`$2'" 1>&2
            exit 1
            ;;
    esac
done