scripts/nbhelper.py

#!/usr/bin/env python3

# SPDX-FileCopyrightText: © 2021 Open Networking Foundation <support@opennetworking.org>
# SPDX-License-Identifier: Apache-2.0

# nbhelper.py
# Helper functions for building YAML output from Netbox API calls

from __future__ import absolute_import

import re
import sys
import argparse
import logging
import netaddr
import pynetbox
import requests

from ruamel import yaml

# create shared logger
logging.basicConfig()
logger = logging.getLogger("nbh")

# to dump YAML properly, using internal representers
# see also:
#  https://stackoverflow.com/questions/54378220/declare-data-type-to-ruamel-yaml-so-that-it-can-represen-serialize-it
#  https://sourceforge.net/p/ruamel-yaml/code/ci/default/tree/representer.py

ydump = yaml.YAML(typ="safe")
ydump.representer.add_representer(
    pynetbox.models.dcim.Devices, yaml.SafeRepresenter.represent_dict
)
ydump.representer.add_representer(
    pynetbox.models.dcim.Interfaces, yaml.SafeRepresenter.represent_dict
)
ydump.representer.add_representer(
    pynetbox.models.ipam.Prefixes, yaml.SafeRepresenter.represent_dict
)
ydump.representer.add_representer(
    pynetbox.core.response.Record, yaml.SafeRepresenter.represent_dict
)
ydump.representer.add_representer(
    pynetbox.models.ipam.IpAddresses, yaml.SafeRepresenter.represent_dict
)
ydump.representer.add_representer(
    pynetbox.core.api.Api, yaml.SafeRepresenter.represent_none
)


def parse_cli_args(extra_args={}):
    """
    parse CLI arguments.  Can add extra arguments with a option:kwargs dict
    """

    parser = argparse.ArgumentParser(description="Netbox")

    # Positional args
    parser.add_argument(
        "settings",
        type=argparse.FileType("r"),
        help="YAML Ansible inventory file w/NetBox API token",
    )

    parser.add_argument(
        "--debug", action="store_true", help="Print additional debugging information"
    )

    if extra_args:
        for ename, ekwargs in extra_args.items():
            parser.add_argument(ename, **ekwargs)

    args = parser.parse_args()

    # only print log messages if debugging
    if args.debug:
        logger.setLevel(logging.DEBUG)
    else:
        logger.setLevel(logging.INFO)

    return args


class AttrDict(dict):
    def __init__(self, *args, **kwargs):
        super(AttrDict, self).__init__(*args, **kwargs)
        self.__dict__ = self


class NBHelper:
    def __init__(self, args):

        self.settings = yaml.safe_load(args.settings.read())

        self.nbapi = pynetbox.api(
            self.settings["api_endpoint"], token=self.settings["token"], threading=True,
        )

        if not self.settings["validate_certs"]:

            session = requests.Session()
            session.verify = False
            self.nbapi.http_session = session

        self.nb_version = self.nbapi.version

    def all_prefixes(self):
        """
        Return a list of prefix objects
        """

        p_items = []

        segments = 1

        if "prefix_segments" in self.settings:
            segments = self.settings["prefix_segments"]

        for prefix in self.settings["ip_prefixes"]:
            p_items.append(NBPrefix.get_prefix(self.nbapi, prefix, segments))

        return p_items

    @classmethod
    def check_name_dns(cls, name):

        badchars = re.search("[^a-z0-9.-]", name.lower(), re.ASCII)

        if badchars:
            logger.error(
                "DNS name '%s' has one or more invalid characters: '%s'",
                name,
                badchars.group(0),
            )
            sys.exit(1)

        return name.lower()

    @classmethod
    def clean_name_dns(cls, name):
        return re.sub("[^a-z0-9.-]", "-", name.lower(), 0, re.ASCII)


@yaml.yaml_object(ydump)
class NBPrefix:

    prefixes = {}

    def __init__(self, api, prefix, name_segments):

        self.nbapi = api
        self.prefix = prefix
        self.name_segments = name_segments

        # get prefix information
        self.prefix_data = self.nbapi.ipam.prefixes.get(prefix=self.prefix)
        self.domain_extension = NBHelper.check_name_dns(self.prefix_data.description)

        logger.debug(
            "prefix %s, domain_extension %s, data: %s",
            self.prefix,
            self.domain_extension,
            dict(self.prefix_data),
        )

        # ip centric info
        self.dhcp_range = None
        self.reserved_ips = {}
        self.aos = {}

        # build item lists
        self.build_prefix()

    @classmethod
    def all_prefixes(cls):
        return cls.prefixes

    @classmethod
    def get_prefix(cls, api, prefix, name_segments=1):
        if prefix in cls.prefixes:
            return cls.prefixes[prefix]

        return NBPrefix(api, prefix, name_segments)

    def __repr__(self):
        return str(self.prefix)

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(
            {
                "dhcp_range": node.dhcp_range,
                "reserved_ips": node.reserved_ips,
                "aos": node.aos,
                "prefix_data": dict(node.prefix_data),
            }
        )

    def parent(self):
        """
        Get the parent prefix to this prefix

        FIXME: Doesn't handle multiple layers of prefixes, returns first found
        """

        # get all parents of this prefix (include self)
        possible_parents = self.nbapi.ipam.prefixes.filter(contains=self.prefix)

        logger.debug("Prefix %s: possible parents %s", self.prefix, possible_parents)

        # filter out self, return first found
        for pparent in possible_parents:
            if pparent.prefix != self.prefix:
                return NBPrefix.get_prefix(
                    self.nbapi, pparent.prefix, self.name_segments
                )

        return None

    def build_prefix(self):
        """
        find ip information for items (devices/vms, reserved_ips, dhcp_range) in prefix
        """

        ips = self.nbapi.ipam.ip_addresses.filter(parent=self.prefix)

        for ip in sorted(ips, key=lambda k: k["address"]):

            logger.debug("prefix_item ip: %s, data: %s", ip, dict(ip))

            # if it's a DHCP range, add that range to the dev list as prefix_dhcp
            if ip.status.value == "dhcp":
                self.dhcp_range = str(ip.address)
                continue

            # reserved IPs
            if ip.status.value == "reserved":

                res = {}
                res["name"] = ip.description.lower().split(" ")[0]
                res["description"] = ip.description
                res["ip4"] = str(netaddr.IPNetwork(ip.address))
                res["custom_fields"] = ip.custom_fields

                self.reserved_ips[str(ip)] = res
                continue

            # devices and VMs
            if ip.assigned_object:  # can be null if not assigned to a device/vm
                aotype = ip.assigned_object_type

                if aotype == "dcim.interface":

                    self.aos[str(ip)] = NBDevice.get_dev(
                        self.nbapi, ip.assigned_object.device.id,
                    )

                elif aotype == "virtualization.vminterface":
                    self.aos[str(ip)] = NBVirtualMachine.get_vm(
                        self.nbapi, ip.assigned_object.virtual_machine.id,
                    )

                else:
                    logger.error("IP %s has unknown device type: %s", ip, aotype)
                    sys.exit(1)

            else:
                logger.warning("Unknown IP type %s, with attributes: %s", ip, dict(ip))


@yaml.yaml_object(ydump)
class NBAssignedObject:
    """
    Assigned Object is either a Device or Virtual Machine, which function
    nearly identically in the NetBox data model.

    This parent class holds common functions for those two child classes
    """

    def __init__(self, api):
        self.nbapi = api

    def dns_name(self, ip, prefix):
        """
        Returns the DNS name for the device at this IP in the prefix
        """

        def first_segment_suffix(split_name, suffixes, segments):
            first_seg = "-".join([split_name[0], *suffixes])

            if segments > 1:
                name = ".".join([first_seg, *split_name[1:segments]])
            else:
                name = first_seg

            return name

        # clean/split the device name
        name_split = NBHelper.clean_name_dns(self.data.name).split(".")

        # always add interface suffix to mgmt interfaces
        if self.interfaces_by_ip[ip].mgmt_only:
            return first_segment_suffix(
                name_split, [self.interfaces_by_ip[ip].name], prefix.name_segments
            )

        # find all IP's for this device in the prefix that aren't mgmt interfaces
        prefix_ips = []
        for s_ip in self.ips:
            if s_ip in prefix.aos and not self.interfaces_by_ip[s_ip].mgmt_only:
                prefix_ips.append(s_ip)

        # name to use when only one IP address for device in a prefix
        simple_name = ".".join(name_split[0 : prefix.name_segments])

        # if more than one non-mgmt IP in prefix
        if len(prefix_ips) > 1:

            # use bare name if primary IP address
            try:  # skip if no primary_ip.address
                if ip == self.data.primary_ip.address:
                    return simple_name
            except AttributeError:
                pass

            # else, suffix with the interface name, and the last octet of IP address
            return first_segment_suffix(
                name_split,
                [
                    self.interfaces_by_ip[ip].name,
                    str(netaddr.IPNetwork(ip).ip.words[3]),
                ],
                prefix.name_segments,
            )

        # simplest case - only one IP in prefix, return simple_name
        return simple_name

    def dns_cnames(self, ip):
        """
        returns a list of cnames for this object, based on IP matches
        """

        cnames = []

        for service in self.services:

            # if not assigned to any IP's, service is on all IPs
            if not service.ipaddresses:
                cnames.append(service.name)
                continue

            # If assigned to an IP, only create a CNAME on that IP
            for service_ip in service.ipaddresses:
                if ip == service_ip.address:
                    cnames.append(service.name)

        return cnames

    def has_service(self, cidr_ip, port, protocol):
        """
        Return True if this AO has a service using specific port and protocol combination
        """

        if (
            cidr_ip in self.interfaces_by_ip
            and not self.interfaces_by_ip[cidr_ip].mgmt_only
        ):
            for service in self.services:
                if service.port == port and service.protocol.value == protocol:
                    return True

        return False

    def primary_iface(self):
        """
        Returns the interface data for the device that has the primary_ip
        """

        if self.data["primary_ip"]:
            return self.interfaces_by_ip[self.data["primary_ip"]["address"]]

        return None


@yaml.yaml_object(ydump)
class NBDevice(NBAssignedObject):
    """
    Wraps a single Netbox device
    Also caches all known devices in a class variable (devs)
    """

    devs = {}

    def __init__(self, api, dev_id):

        super().__init__(api)

        self.id = dev_id
        self.data = self.nbapi.dcim.devices.get(dev_id)
        self.services = self.nbapi.ipam.services.filter(device_id=dev_id)

        # not filled in unless specifically asked for (expensive for a 48 port switch)
        self.interfaces = []
        self.mgmt_interfaces = []

        # look up all IP's for this device
        self.ips = {
            str(ip): ip for ip in self.nbapi.ipam.ip_addresses.filter(device_id=dev_id)
        }

        # look up interfaces by IP
        self.interfaces_by_ip = {}
        for ip, ip_data in self.ips.items():
            if ip_data.assigned_object:
                self.interfaces_by_ip[ip] = self.nbapi.dcim.interfaces.get(
                    ip_data.assigned_object_id
                )

        logger.debug(
            "NBDevice id: %d, data: %s, ips: %s", self.id, dict(self.data), self.ips,
        )

        self.devs[dev_id] = self

    def __repr__(self):
        return str(dict(self.data))

    def get_interfaces(self):
        if not self.interfaces:
            self.interfaces = self.nbapi.dcim.interfaces.filter(device_id=self.id)

        return self.interfaces

    @classmethod
    def get_dev(cls, api, dev_id):
        if dev_id in cls.devs:
            return cls.devs[dev_id]

        return NBDevice(api, dev_id)

    @classmethod
    def all_devs(cls):
        return cls.devs

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(
            {
                "data": node.data,
                "services": node.services,
                "ips": node.ips,
                "interfaces_by_ip": node.interfaces_by_ip,
            }
        )


@yaml.yaml_object(ydump)
class NBVirtualMachine(NBAssignedObject):
    """
    VM equivalent of NBDevice
    """

    vms = {}

    def __init__(self, api, vm_id):

        super().__init__(api)

        self.id = vm_id
        self.data = self.nbapi.virtualization.virtual_machines.get(vm_id)
        self.services = self.nbapi.ipam.services.filter(virtual_machine_id=vm_id)

        # not filled in unless specifically asked for
        self.interfaces = []

        # look up all IP's for this device
        self.ips = {
            str(ip): ip
            for ip in self.nbapi.ipam.ip_addresses.filter(virtual_machine_id=vm_id)
        }

        # look up interfaces by IP
        self.interfaces_by_ip = {}
        for ip, ip_data in self.ips.items():
            if ip_data.assigned_object:
                self.interfaces_by_ip[ip] = self.nbapi.virtualization.interfaces.get(
                    ip_data.assigned_object_id
                )
                # hack as VM interfaces lack this key, and needed for services
                self.interfaces_by_ip[ip].mgmt_only = False

        logger.debug(
            "NBVirtualMachine id: %d, data: %s, ips: %s",
            self.id,
            dict(self.data),
            self.ips,
        )

        self.vms[vm_id] = self

    def __repr__(self):
        return str(dict(self.data))

    def get_interfaces(self):
        if not self.interfaces:
            self.interfaces = self.nbapi.virtualization.interfaces.filter(
                virtual_machine_id=self.id
            )

        return self.interfaces

    @classmethod
    def get_vm(cls, api, vm_id):
        if vm_id in cls.vms:
            return cls.vms[vm_id]

        return NBVirtualMachine(api, vm_id)

    @classmethod
    def all_vms(cls):
        return cls.vms

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(
            {
                "data": node.data,
                "services": node.services,
                "ips": node.ips,
                "interfaces_by_ip": node.interfaces_by_ip,
            }
        )


@yaml.yaml_object(ydump)
class NBDNSForwardZone:

    fwd_zones = {}

    def __init__(self, prefix):

        self.domain_extension = prefix.domain_extension

        self.a_recs = {}
        self.cname_recs = {}
        self.srv_recs = {}
        self.ns_recs = []
        self.txt_recs = {}

        if prefix.dhcp_range:
            self.create_dhcp_fwd(prefix.dhcp_range)

        for ip, ao in prefix.aos.items():
            self.add_ao_records(prefix, ip, ao)

        for ip, res in prefix.reserved_ips.items():
            self.add_reserved(ip, res)

        # reqquired for the add_fwd_cname function below
        if callable(getattr(prefix, "parent")):
            parent_prefix = prefix.parent()

            if parent_prefix:
                self.merge_parent_prefix(parent_prefix, prefix)

        self.fwd_zones[self.domain_extension] = self

    def __repr__(self):
        return str(
            {
                "a": self.a_recs,
                "cname": self.cname_recs,
                "ns": self.ns_recs,
                "srv": self.srv_recs,
                "txt": self.txt_recs,
            }
        )

    @classmethod
    def add_fwd_cname(cls, cname, fqdn_dest):
        """
        Add an arbitrary CNAME (and possibly create the fwd zone if needed) pointing
        at a FQDN destination name. It's used to support the per-IP "DNS name" field in NetBox
        Note that the NS record
        """

        try:
            fqdn_split = re.compile(r"([a-z]+)\.([a-z.]+)\.")
            (short_name, extension) = fqdn_split.match(cname).groups()

        except AttributeError:
            logger.warning(
                "Invalid DNS CNAME: '%s', must be in FQDN format: 'host.example.com.', ignored",
                cname,
            )
            return

        fake_prefix = AttrDict(
            {
                "domain_extension": extension,
                "dhcp_range": None,
                "aos": {},
                "reserved_ips": {},
                "parent": None,
            }
        )

        fwd_zone = cls.get_fwd_zone(fake_prefix)

        fwd_zone.cname_recs[short_name] = fqdn_dest

    @classmethod
    def get_fwd_zone(cls, prefix):
        if prefix.domain_extension in cls.fwd_zones:
            return cls.fwd_zones[prefix.domain_extension]

        return NBDNSForwardZone(prefix)

    @classmethod
    def all_fwd_zones(cls):
        return cls.fwd_zones

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(
            {
                "a": node.a_recs,
                "cname": node.cname_recs,
                "ns": node.ns_recs,
                "srv": node.srv_recs,
                "txt": node.txt_recs,
            }
        )

    def fqdn(self, name):
        return "%s.%s." % (name, self.domain_extension)

    def create_dhcp_fwd(self, dhcp_range):

        for ip in netaddr.IPNetwork(dhcp_range).iter_hosts():
            self.a_recs["dhcp%03d" % (ip.words[3])] = str(ip)

    def name_is_duplicate(self, name, target, record_type):
        """
        Returns True if name already exists in the zone as an A or CNAME
        record, False otherwise
        """

        if name in self.a_recs:
            logger.warning(
                "Duplicate DNS record for name %s - A record to '%s', %s record to '%s'",
                name,
                self.a_recs[name],
                record_type,
                target,
            )
            return True

        if name in self.cname_recs:
            logger.warning(
                "Duplicate DNS record for name %s - CNAME record to '%s', %s record to '%s'",
                name,
                self.cname_recs[name],
                record_type,
                target,
            )
            return True

        return False

    def add_ao_records(self, prefix, ip, ao):

        name = ao.dns_name(ip, prefix)
        target_ip = str(netaddr.IPNetwork(ip).ip)  # make bare IP, not CIDR format

        # add A records
        if not self.name_is_duplicate(name, target_ip, "A"):
            self.a_recs[name] = target_ip

        # add CNAME records that alias to this name
        for cname in ao.dns_cnames(ip):
            # check that it isn't a dupe
            if not self.name_is_duplicate(cname, target_ip, "CNAME"):
                self.cname_recs[cname] = self.fqdn(name)

        # add NS records if this is a DNS server
        if ao.has_service(ip, 53, "udp"):
            self.ns_recs.append(self.fqdn(name))

        # if a DNS name is set, add it as a CNAME
        if ao.ips[ip]["dns_name"]:  # and ip == aos.data.primary_ip.address:
            self.add_fwd_cname(ao.ips[ip]["dns_name"], self.fqdn(name))

    def add_reserved(self, ip, res):

        target_ip = str(netaddr.IPNetwork(ip).ip)  # make bare IP, not CIDR format

        if not self.name_is_duplicate(res["name"], target_ip, "A"):
            self.a_recs[res["name"]] = target_ip

    def merge_parent_prefix(self, pprefix, prefix):

        # only if no NS records exist already
        if not self.ns_recs:
            # scan parent prefix for services
            for ip, ao in pprefix.aos.items():

                # Create a DNS within this prefix pointing to out-of-prefix IP
                # where DNS server is
                name = ao.dns_name(ip, prefix)
                target_ip = str(
                    netaddr.IPNetwork(ip).ip
                )  # make bare IP, not CIDR format

                # add NS records if this is a DNS server
                if ao.has_service(ip, 53, "udp"):
                    self.a_recs[name] = target_ip
                    self.ns_recs.append(self.fqdn(name))


@yaml.yaml_object(ydump)
class NBDNSReverseZones:
    def __init__(self):

        self.reverse_zones = {}

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(node.reverse_zones)

    @classmethod
    def canonicalize_rfc1918_prefix(cls, prefix):
        """
        RFC1918 prefixes need to be expanded to their widest canonical range to
        group all reverse lookup domains together for reverse DNS with NSD/Unbound.
        """

        pnet = netaddr.IPNetwork(str(prefix))
        (o1, o2, o3, o4) = pnet.network.words  # Split ipv4 octets
        cidr_plen = pnet.prefixlen

        if o1 == 10:
            o2 = o3 = o4 = 0
            cidr_plen = 8
        elif (o1 == 172 and o2 >= 16 and o2 <= 31) or (o1 == 192 and o2 == 168):
            o3 = o4 = 0
            cidr_plen = 16

        return "%s/%d" % (".".join(map(str, [o1, o2, o3, o4])), cidr_plen)

    def add_prefix(self, prefix):

        canonical_prefix = self.canonicalize_rfc1918_prefix(prefix)

        if canonical_prefix in self.reverse_zones:
            rzone = self.reverse_zones[canonical_prefix]
        else:
            rzone = {
                "ns": [],
                "ptr": {},
            }

        if prefix.dhcp_range:
            # FIXME: doesn't check for duplicate entries
            rzone["ptr"].update(self.create_dhcp_rev(prefix))

        for ip, ao in prefix.aos.items():
            target_ip = str(netaddr.IPNetwork(ip).ip)  # make bare IP, not CIDR format
            ao_name = self.get_ao_name(ip, ao, prefix,)
            rzone["ptr"][target_ip] = ao_name

            # add NS records if this is a DNS server
            if ao.has_service(ip, 53, "udp"):
                rzone["ns"].append(ao_name)

        parent_prefix = prefix.parent()

        if parent_prefix:
            self.merge_parent_prefix(rzone, parent_prefix)

        self.reverse_zones[canonical_prefix] = rzone

    def merge_parent_prefix(self, rzone, pprefix):

        # parent items
        p_ns = []

        # scan parent prefix for services
        for ip, ao in pprefix.aos.items():

            ao_name = self.get_ao_name(ip, ao, pprefix,)

            # add NS records if this is a DNS server
            if ao.has_service(ip, 53, "udp"):
                p_ns.append(ao_name)

        # set DNS servers if none in rzone
        if not rzone["ns"]:
            rzone["ns"] = p_ns

    def create_dhcp_rev(self, prefix):

        dhcp_rzone = {}

        for ip in netaddr.IPNetwork(prefix.dhcp_range).iter_hosts():
            dhcp_rzone[str(ip)] = "dhcp%03d.%s." % (
                ip.words[3],
                prefix.domain_extension,
            )

        return dhcp_rzone

    def get_ao_name(self, ip, ao, prefix):
        short_name = ao.dns_name(ip, prefix)
        return "%s.%s." % (short_name, prefix.domain_extension)


@yaml.yaml_object(ydump)
class NBDHCPSubnet:
    def __init__(self, prefix):

        self.domain_extension = prefix.domain_extension

        self.subnet = None
        self.range = None
        self.first_ip = None
        self.hosts = []
        self.routers = []
        self.dns_servers = []
        self.dns_search = []
        self.tftpd_server = None
        self.ntp_servers = []
        self.dhcpd_interface = None

        self.add_prefix(prefix)

        for ip, ao in prefix.aos.items():
            self.add_ao(str(ip), ao, prefix)

        parent_prefix = prefix.parent()

        if parent_prefix:
            self.merge_parent_prefix(parent_prefix)

    def add_prefix(self, prefix):

        self.subnet = str(prefix)

        self.first_ip = str(netaddr.IPAddress(netaddr.IPNetwork(str(prefix)).first + 1))

        self.dns_search = [prefix.domain_extension]

        if prefix.dhcp_range:
            self.range = prefix.dhcp_range

        for ip, res in prefix.reserved_ips.items():
            # routers are reserved IP's that start with 'router" in the IP description
            if re.match("router", res["description"]):
                router = {"ip": str(netaddr.IPNetwork(ip).ip)}

                if (
                    "rfc3442routes" in res["custom_fields"]
                    and res["custom_fields"]["rfc3442routes"]
                ):
                    # split on whitespace
                    router["rfc3442routes"] = re.split(
                        r"\s+", res["custom_fields"]["rfc3442routes"]
                    )

                self.routers.append(router)

        # set first IP to router if not set otherwise.
        if not self.routers:
            router = {"ip": self.first_ip}

            self.routers.append(router)

    def add_ao(self, ip, ao, prefix):

        target_ip = str(netaddr.IPNetwork(ip).ip)  # make bare IP, not CIDR format

        # find the DHCP interface if it's this IP
        if target_ip == self.first_ip:
            self.dhcpd_interface = ao.interfaces_by_ip[ip].name

        name = ao.dns_name(ip, prefix)

        # add only devices that have a macaddr for this IP
        if ip in ao.interfaces_by_ip:

            mac_addr = dict(ao.interfaces_by_ip[ip]).get("mac_address")

            if mac_addr and mac_addr.strip():  # if exists and not blank
                self.hosts.append(
                    {"name": name, "ip_addr": target_ip, "mac_addr": mac_addr.lower(),}
                )

        # add dns servers
        if ao.has_service(ip, 53, "udp"):
            self.dns_servers.append(target_ip)

        # add tftp server
        if ao.has_service(ip, 69, "udp"):
            if not self.tftpd_server:
                self.tftpd_server = target_ip
            else:
                logger.warning(
                    "Duplicate TFTP servers in prefix, using first of %s and %s",
                    self.tftpd_server,
                    target_ip,
                )

        # add NTP servers
        if ao.has_service(ip, 123, "udp"):
            self.ntp_servers.append(target_ip)

    def merge_parent_prefix(self, pprefix):

        # parent items
        p_dns_servers = []
        p_tftpd_server = None
        p_ntp_servers = []

        # scan parent prefix for services
        for ip, ao in pprefix.aos.items():

            target_ip = str(netaddr.IPNetwork(ip).ip)

            # add dns servers
            if ao.has_service(ip, 53, "udp"):
                p_dns_servers.append(target_ip)

            # add tftp server
            if ao.has_service(ip, 69, "udp"):
                if not p_tftpd_server:
                    p_tftpd_server = target_ip
                else:
                    logger.warning(
                        "Duplicate TFTP servers in parent prefix, using first of %s and %s",
                        p_tftpd_server,
                        target_ip,
                    )

            # add NTP servers
            if ao.has_service(ip, 123, "udp"):
                p_ntp_servers.append(target_ip)

        # merge if doesn't exist in prefix
        if not self.dns_servers:
            self.dns_servers = p_dns_servers

        if not self.tftpd_server:
            self.tftpd_server = p_tftpd_server

        if not self.ntp_servers:
            self.ntp_servers = p_ntp_servers

    @classmethod
    def to_yaml(cls, representer, node):
        return representer.represent_dict(
            {
                "subnet": node.subnet,
                "range": node.range,
                "routers": node.routers,
                "hosts": node.hosts,
                "dns_servers": node.dns_servers,
                "dns_search": node.dns_search,
                "tftpd_server": node.tftpd_server,
                "ntp_servers": node.ntp_servers,
            }
        )