Listens for networkd signals and deprecate the ip6 route on the interface when the interface gets reconfigured

ipda.py

#!/usr/bin/env python3

from functools import cache

import argparse
import dbus
import subprocess
import json

import dbus.mainloop.glib
from gi.repository import GLib as glib

IFACE = None
PREFIX = None


def ip_addr_show(dev):
    cmd = ['ip', '-j', '-6', 'addr', 'show', 'dev', dev]
    p = subprocess.run(cmd, capture_output=True, check=True)
    stdout = p.stdout.decode('utf-8')
    return json.loads(stdout)


def deprecate_address(dev, prefix):
    addrs = [x for x in ip_addr_show(dev)[0]['addr_info']
             if x['local'].startswith(prefix)]

    if not len(addrs):
        print(f"address matching {prefix} on {dev} not found")
        return

    # Deprecate all matching Addresses
    for addr in addrs:
        if addr['preferred_life_time'] == 0:
            return

        local = str(addr['local'])
        valid = str(addr['valid_life_time'])

        cmd = ['ip', 'addr', 'change', local, 'dev', dev, 'valid_lft', valid, 'preferred_lft', '0']
        subprocess.run(cmd, capture_output=True, check=True)
        print(f"{dev}: deprecated {local} valid_lft {valid} preferred_lft 0")
    return


@cache
def get_ifindex(dev):
    with open(f"/sys/class/net/{dev}/ifindex") as fd:
        idx = fd.readline().strip()
    return idx


def property_changed(typ, data, _, path):
    if typ != 'org.freedesktop.network1.Link':
        return
    if not path.startswith('/org/freedesktop/network1/link/_'):
        return

    idx = path.replace('/org/freedesktop/network1/link/_', '').split('/')[0]
    idx = chr(int(idx[:2], 16))

    try:
        ifindex = get_ifindex(IFACE)
    except IOError:
        return

    # Ignore changes for interfaces we don't care about
    if idx != ifindex:
        return

    # When address lifetime is refreshed, the AdministrativeState property
    # changes to 'configuring', then transitions to 'configured'
    if data.get('AdministrativeState') != 'configured':
        return

    deprecate_address(IFACE, PREFIX)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description='deprecate ip6 address')
    parser.add_argument('-i', '--interface', required=True,
                        help='interface to deprecate address on')
    parser.add_argument('-p', '--prefix', default='2001:506',
                        help='address prefix to match against')
    args = parser.parse_args()

    IFACE = args.interface
    PREFIX = args.prefix

    dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
    bus = dbus.SystemBus()
    bus.add_signal_receiver(property_changed,
                            bus_name='org.freedesktop.network1',
                            signal_name='PropertiesChanged',
                            path_keyword='path')

    print("Monitoring org.freedesktop.network1")
    mainloop = glib.MainLoop()
    mainloop.run()