def mcastIp2McastMac(ip):
    """ Convert a dot-notated IPv4 multicast address string into an multicast MAC address"""
    digits = [int(d) for d in ip.split('.')]
    return '01:00:5e:%02x:%02x:%02x' % (digits[1] & 0x7f, digits[2] & 0xff, digits[3] & 0xff)