def decode_ip_addr(ipaddr):
    """Convert 32-bit numeric IPv4 address to string of 4 dot-separated octets."""
    d = ipaddr & 0xff
    ipaddr >>= 8
    c = ipaddr & 0xff
    ipaddr >>= 8
    b = ipaddr & 0xff
    ipaddr >>= 8
    a = ipaddr & 0xff
    return str(a) + "." + str(b) + "." + str(c) + "." + str(d)