Generate systemd nspawn interface MAC aadresses based on the host id and container name https://wiki.wut.ee/sysadmin/systemd-nspawn_containers

make_nspawn_iface_mac.py

#!/usr/bin/env python3
"""
This script implements systemd-nspawn MAC aadress generation algorithm
"""

import sys
import struct
from subprocess import run

import siphashc  # https://pypi.org/project/siphashc/


# from src/nspawn/nspawn-network.c
# -n,--network-veth
# host side of vb-/ve- interface
HOST_HASH_KEY = bytes.fromhex("1a376fc746ec450bada3d53106605db1")
# container side of vb-/ve- interface
CONTAINER_HASH_KEY = bytes.fromhex("c3c4f919b557b21ce6cf1427039ceea2")
# --network-veth-extra
VETH_EXTRA_HOST_HASH_KEY = bytes.fromhex("48c7f6b7ea9d4c9eb728d4de91d5bf66")
VETH_EXTRA_CONTAINER_HASH_KEY = bytes.fromhex("af501761cef94d35840d2b2054bece59")
# --network-macvlan
MACVLAN_HASH_KEY = bytes.fromhex("00136dbc66834481bb0cf9511f24a66f")
# used when interface name is too long
SHORTEN_IFNAME_HASH_KEY = bytes.fromhex("e190a404a8ef4b518cccc33a9f11fca2")


# Based on systemd src/nspawn/nspawn-network.c
def generate_mac(machine_id, machine_name, hash_key, idx=0):
    if type(machine_name) == str:
        machine_name = machine_name.encode()
    if idx > 0:
        v = machine_id + struct.pack('<Q', idx) + machine_name
    else:
        v = machine_id + machine_name

    result = siphashc.siphash(hash_key, v).to_bytes(8, byteorder='little')

    mac = bytearray(result[:6])
    mac[0] &= 0xfe;  # clear multicast bit
    mac[0] |= 0x02;  # set local assignment bit (IEEE802)
    return bytes(mac)


def format_mac(mac):
    if type(mac) == bytes:
        mac = mac.hex()
    l = []
    for idx in range(0, len(mac), 2):
        l.append(mac[idx:idx+2])
    return ":".join(l)


if __name__ == "__main__":
    if len(sys.argv) == 3:
        machine_id = bytes.fromhex(sys.argv[1])
        machine_name = sys.argv[2]
    elif len(sys.argv) == 2:
        machine_name = sys.argv[1]
        machine_id_proc = run(["systemd-id128", "machine-id"], capture_output=True, text=True)
        machine_id = bytes.fromhex(machine_id_proc.stdout.strip())
    else:
        print("Usage: {} [machine-id] machine-name".format(sys.argv[0]), file=sys.stderr)
        sys.exit(1)
    mac = generate_mac(machine_id, machine_name, CONTAINER_HASH_KEY)
    print(format_mac(mac))