def mac_addr_is_unicast(mac_addr):
    """Returns True if mac_addr is a unicast Ethernet address.

    Args:
        mac_addr (str): MAC address.
    Returns:
        bool: True if a unicast Ethernet address.
    """
    msb = mac_addr.split(':')[0]
    return msb[-1] in '02468aAcCeE'