def ipv6(mac_addr):
    """
    Convert MAC into IPv6 format.

    E.g. 2e:ff:ff:00:22:8b to 2eff:ff00:228b

    :type mac_addr: str
    :rtype: str
    """
    bytes = mac_addr.replace(':', '')
    ip = ''
    for index, part in enumerate(bytes):
        ip += part
        if index % 4 == 3 and index < len(bytes) - 1:
            ip += ':'
    # Prefix from border router
    return 'fdfd::221:' + ip