import struct


def inet_aton(string):
    """inet_aton(string) -> packed 32-bit IP representation

    Convert an IP address in string format (123.45.67.89) to the 32-bit packed
    binary format used in low-level network functions."""
    a, b, c, d = map(int, string.split(".", 3))
    return struct.pack("BBBB", a, b, c, d)