def ip_to_num(ip):
    ip=[int(x) for in ip.split('.')]
    return ip[0] <<24 | ip[1]<<16 | ip[2]<<8 |ip[3]
def num_to_ip(num):
    return '%s.%s.%s.%s' %( (num & 0xff000000) >>24,
                            (num & 0x00ff0000) >>16,
                            (num & 0x0000ff00) >>8,
                            num & 0x000000ff )