def ipv4_is_defined(address):
    """
    The function for checking if an IPv4 address is defined (does not need to
    be resolved).

    Args:
        address (:obj:`str`): An IPv4 address.

    Returns:
        namedtuple:

        :is_defined (bool): True if given address is defined, otherwise
            False
        :ietf_name (str): IETF assignment name if given address is
            defined, otherwise ''
        :ietf_rfc (str): IETF assignment RFC if given address is defined,
            otherwise ''
    """

    # Initialize the IP address object.
    query_ip = IPv4Address(str(address))

    # Initialize the results named tuple
    results = namedtuple('ipv4_is_defined_results', 'is_defined, ietf_name, '
                                                    'ietf_rfc')

    # This Network
    if query_ip in IPv4Network('0.0.0.0/8'):

        return results(True, 'This Network', 'RFC 1122, Section 3.2.1.3')

    # Loopback
    elif query_ip.is_loopback:

        return results(True, 'Loopback', 'RFC 1122, Section 3.2.1.3')

    # Link Local
    elif query_ip.is_link_local:

        return results(True, 'Link Local', 'RFC 3927')

    # IETF Protocol Assignments
    elif query_ip in IPv4Network('192.0.0.0/24'):

        return results(True, 'IETF Protocol Assignments', 'RFC 5736')

    # TEST-NET-1
    elif query_ip in IPv4Network('192.0.2.0/24'):

        return results(True, 'TEST-NET-1', 'RFC 5737')

    # 6to4 Relay Anycast
    elif query_ip in IPv4Network('192.88.99.0/24'):

        return results(True, '6to4 Relay Anycast', 'RFC 3068')

    # Network Interconnect Device Benchmark Testing
    elif query_ip in IPv4Network('198.18.0.0/15'):

        return (results(True,
                'Network Interconnect Device Benchmark Testing',
                        'RFC 2544'))

    # TEST-NET-2
    elif query_ip in IPv4Network('198.51.100.0/24'):

        return results(True, 'TEST-NET-2', 'RFC 5737')

    # TEST-NET-3
    elif query_ip in IPv4Network('203.0.113.0/24'):

        return results(True, 'TEST-NET-3', 'RFC 5737')

    # Multicast
    elif query_ip.is_multicast:

        return results(True, 'Multicast', 'RFC 3171')

    # Limited Broadcast
    elif query_ip in IPv4Network('255.255.255.255/32'):

        return results(True, 'Limited Broadcast', 'RFC 919, Section 7')

    # Private-Use Networks
    elif query_ip.is_private:

        return results(True, 'Private-Use Networks', 'RFC 1918')

    # New IANA Reserved
    # TODO: Someone needs to find the RFC for this
    elif query_ip in IPv4Network('198.97.38.0/24'):

        return results(True, 'IANA Reserved', '')

    return results(False, '', '')
The function for checking if an IPv4 address is defined (does not need to
    be resolved).

    Args:
        address (:obj:`str`): An IPv4 address.

    Returns:
        namedtuple:

        :is_defined (bool): True if given address is defined, otherwise
            False
        :ietf_name (str): IETF assignment name if given address is
            defined, otherwise ''
        :ietf_rfc (str): IETF assignment RFC if given address is defined,
            otherwise ''