def format_general_name(name):
    """Format a single general name.

    >>> import ipaddress
    >>> format_general_name(x509.DNSName('example.com'))
    'DNS:example.com'
    >>> format_general_name(x509.IPAddress(ipaddress.IPv4Address('127.0.0.1')))
    'IP:127.0.0.1'
    """

    if isinstance(name, x509.DirectoryName):
        value = format_name(name.value)
    else:
        value = name.value
    return '%s:%s' % (SAN_NAME_MAPPINGS[type(name)], value)