text: from __future__ import unicode_literals
  
  from collections import OrderedDict
  from itertools import count, groupby
  
  from django.conf import settings
  from django.contrib.auth.models import User
  from django.contrib.contenttypes.fields import GenericRelation
  from django.contrib.postgres.fields import ArrayField, JSONField
  from django.core.exceptions import ObjectDoesNotExist, ValidationError
  from django.core.validators import MaxValueValidator, MinValueValidator
  from django.db import models
  from django.db.models import Count, Q, ObjectDoesNotExist
  from django.urls import reverse
  from django.utils.encoding import python_2_unicode_compatible
  from mptt.models import MPTTModel, TreeForeignKey
  from taggit.managers import TaggableManager
  from timezone_field import TimeZoneField
  
  from circuits.models import Circuit
  from extras.constants import OBJECTCHANGE_ACTION_DELETE, OBJECTCHANGE_ACTION_UPDATE
  from extras.models import ConfigContextModel, CustomFieldModel, ObjectChange
  from extras.rpc import RPC_CLIENTS
  from utilities.fields import ColorField, NullableCharField
  from utilities.managers import NaturalOrderByManager
  from utilities.models import ChangeLoggedModel
  from utilities.utils import serialize_object
  from .constants import *
  from .fields import ASNField, MACAddressField
  from .querysets import InterfaceQuerySet
  
  
  class ComponentModel(models.Model):
  
      class Meta:
          abstract = True
  
      def get_component_parent(self):
          raise NotImplementedError(
              "ComponentModel must implement get_component_parent()"
          )
  
      def log_change(self, user, request_id, action):
          """
          Log an ObjectChange including the parent Device/VM.
          """
          ObjectChange(
              user=user,
              request_id=request_id,
              changed_object=self,
              related_object=self.get_component_parent(),
              action=action,
              object_data=serialize_object(self)
          ).save()
  
  
  #
  # Regions
  #
  
  @python_2_unicode_compatible
  class Region(MPTTModel, ChangeLoggedModel):
      """
      Sites can be grouped within geographic Regions.
      """
      parent = TreeForeignKey(
          to='self',
          on_delete=models.CASCADE,
          related_name='children',
          blank=True,
          null=True,
          db_index=True
      )
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
  
      csv_headers = ['name', 'slug', 'parent']
  
      class MPTTMeta:
          order_insertion_by = ['name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return "{}?region={}".format(reverse('dcim:site_list'), self.slug)
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
              self.parent.name if self.parent else None,
          )
  
  
  #
  # Sites
  #
  
  class SiteManager(NaturalOrderByManager):
      natural_order_field = 'name'
  
  
  @python_2_unicode_compatible
  class Site(ChangeLoggedModel, CustomFieldModel):
      """
      A Site represents a geographic location within a network; typically a building or campus. The optional facility
      field can be used to include an external designation, such as a data center name (e.g. Equinix SV6).
      """
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
      status = models.PositiveSmallIntegerField(
          choices=SITE_STATUS_CHOICES,
          default=SITE_STATUS_ACTIVE
      )
      region = models.ForeignKey(
          to='dcim.Region',
          on_delete=models.SET_NULL,
          related_name='sites',
          blank=True,
          null=True
      )
      tenant = models.ForeignKey(
          to='tenancy.Tenant',
          on_delete=models.PROTECT,
          related_name='sites',
          blank=True,
          null=True
      )
      facility = models.CharField(
          max_length=50,
          blank=True
      )
      asn = ASNField(
          blank=True,
          null=True,
          verbose_name='ASN'
      )
      time_zone = TimeZoneField(
          blank=True
      )
      description = models.CharField(
          max_length=100,
          blank=True
      )
      physical_address = models.CharField(
          max_length=200,
          blank=True
      )
      shipping_address = models.CharField(
          max_length=200,
          blank=True
      )
      latitude = models.DecimalField(
          max_digits=8,
          decimal_places=6,
          blank=True,
          null=True
      )
      longitude = models.DecimalField(
          max_digits=9,
          decimal_places=6,
          blank=True,
          null=True
      )
      contact_name = models.CharField(
          max_length=50,
          blank=True
      )
      contact_phone = models.CharField(
          max_length=20,
          blank=True
      )
      contact_email = models.EmailField(
          blank=True,
          verbose_name='Contact E-mail'
      )
      comments = models.TextField(
          blank=True
      )
      custom_field_values = GenericRelation(
          to='extras.CustomFieldValue',
          content_type_field='obj_type',
          object_id_field='obj_id'
      )
      images = GenericRelation(
          to='extras.ImageAttachment'
      )
  
      objects = SiteManager()
      tags = TaggableManager()
  
      csv_headers = [
          'name', 'slug', 'status', 'region', 'tenant', 'facility', 'asn', 'time_zone', 'description', 'physical_address',
          'shipping_address', 'latitude', 'longitude', 'contact_name', 'contact_phone', 'contact_email', 'comments',
      ]
  
      class Meta:
          ordering = ['name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return reverse('dcim:site', args=[self.slug])
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
              self.get_status_display(),
              self.region.name if self.region else None,
              self.tenant.name if self.tenant else None,
              self.facility,
              self.asn,
              self.time_zone,
              self.description,
              self.physical_address,
              self.shipping_address,
              self.latitude,
              self.longitude,
              self.contact_name,
              self.contact_phone,
              self.contact_email,
              self.comments,
          )
  
      def get_status_class(self):
          return STATUS_CLASSES[self.status]
  
      @property
      def count_prefixes(self):
          return self.prefixes.count()
  
      @property
      def count_vlans(self):
          return self.vlans.count()
  
      @property
      def count_racks(self):
          return Rack.objects.filter(site=self).count()
  
      @property
      def count_devices(self):
          return Device.objects.filter(site=self).count()
  
      @property
      def count_circuits(self):
          return Circuit.objects.filter(terminations__site=self).count()
  
      @property
      def count_vms(self):
          from virtualization.models import VirtualMachine
          return VirtualMachine.objects.filter(cluster__site=self).count()
  
  
  #
  # Racks
  #
  
  @python_2_unicode_compatible
  class RackGroup(ChangeLoggedModel):
      """
      Racks can be grouped as subsets within a Site. The scope of a group will depend on how Sites are defined. For
      example, if a Site spans a corporate campus, a RackGroup might be defined to represent each building within that
      campus. If a Site instead represents a single building, a RackGroup might represent a single room or floor.
      """
      name = models.CharField(
          max_length=50
      )
      slug = models.SlugField()
      site = models.ForeignKey(
          to='dcim.Site',
          on_delete=models.CASCADE,
          related_name='rack_groups'
      )
  
      csv_headers = ['site', 'name', 'slug']
  
      class Meta:
          ordering = ['site', 'name']
          unique_together = [
              ['site', 'name'],
              ['site', 'slug'],
          ]
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return "{}?group_id={}".format(reverse('dcim:rack_list'), self.pk)
  
      def to_csv(self):
          return (
              self.site,
              self.name,
              self.slug,
          )
  
  
  @python_2_unicode_compatible
  class RackRole(ChangeLoggedModel):
      """
      Racks can be organized by functional role, similar to Devices.
      """
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
      color = ColorField()
  
      csv_headers = ['name', 'slug', 'color']
  
      class Meta:
          ordering = ['name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return "{}?role={}".format(reverse('dcim:rack_list'), self.slug)
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
              self.color,
          )
  
  
  class RackManager(NaturalOrderByManager):
      natural_order_field = 'name'
  
  
  @python_2_unicode_compatible
  class Rack(ChangeLoggedModel, CustomFieldModel):
      """
      Devices are housed within Racks. Each rack has a defined height measured in rack units, and a front and rear face.
      Each Rack is assigned to a Site and (optionally) a RackGroup.
      """
      name = models.CharField(
          max_length=50
      )
      facility_id = NullableCharField(
          max_length=50,
          blank=True,
          null=True,
          verbose_name='Facility ID'
      )
      site = models.ForeignKey(
          to='dcim.Site',
          on_delete=models.PROTECT,
          related_name='racks'
      )
      group = models.ForeignKey(
          to='dcim.RackGroup',
          on_delete=models.SET_NULL,
          related_name='racks',
          blank=True,
          null=True
      )
      tenant = models.ForeignKey(
          to='tenancy.Tenant',
          on_delete=models.PROTECT,
          related_name='racks',
          blank=True,
          null=True
      )
      role = models.ForeignKey(
          to='dcim.RackRole',
          on_delete=models.PROTECT,
          related_name='racks',
          blank=True,
          null=True
      )
      serial = models.CharField(
          max_length=50,
          blank=True,
          verbose_name='Serial number'
      )
      type = models.PositiveSmallIntegerField(
          choices=RACK_TYPE_CHOICES,
          blank=True,
          null=True,
          verbose_name='Type'
      )
      width = models.PositiveSmallIntegerField(
          choices=RACK_WIDTH_CHOICES,
          default=RACK_WIDTH_19IN,
          verbose_name='Width',
          help_text='Rail-to-rail width'
      )
      u_height = models.PositiveSmallIntegerField(
          default=42,
          verbose_name='Height (U)',
          validators=[MinValueValidator(1), MaxValueValidator(100)]
      )
      desc_units = models.BooleanField(
          default=False,
          verbose_name='Descending units',
          help_text='Units are numbered top-to-bottom'
      )
      comments = models.TextField(
          blank=True
      )
      custom_field_values = GenericRelation(
          to='extras.CustomFieldValue',
          content_type_field='obj_type',
          object_id_field='obj_id'
      )
      images = GenericRelation(
          to='extras.ImageAttachment'
      )
  
      objects = RackManager()
      tags = TaggableManager()
  
      csv_headers = [
          'site', 'group_name', 'name', 'facility_id', 'tenant', 'role', 'type', 'serial', 'width', 'u_height',
          'desc_units', 'comments',
      ]
  
      class Meta:
          ordering = ['site', 'group', 'name']
          unique_together = [
              ['group', 'name'],
              ['group', 'facility_id'],
          ]
  
      def __str__(self):
          return self.display_name or super(Rack, self).__str__()
  
      def get_absolute_url(self):
          return reverse('dcim:rack', args=[self.pk])
  
      def clean(self):
  
          if self.pk:
              # Validate that Rack is tall enough to house the installed Devices
              top_device = Device.objects.filter(rack=self).exclude(position__isnull=True).order_by('-position').first()
              if top_device:
                  min_height = top_device.position + top_device.device_type.u_height - 1
                  if self.u_height < min_height:
                      raise ValidationError({
                          'u_height': "Rack must be at least {}U tall to house currently installed devices.".format(
                              min_height
                          )
                      })
              # Validate that Rack was assigned a group of its same site, if applicable
              if self.group:
                  if self.group.site != self.site:
                      raise ValidationError({
                          'group': "Rack group must be from the same site, {}.".format(self.site)
                      })
  
      def save(self, *args, **kwargs):
  
          # Record the original site assignment for this rack.
          _site_id = None
          if self.pk:
              _site_id = Rack.objects.get(pk=self.pk).site_id
  
          super(Rack, self).save(*args, **kwargs)
  
          # Update racked devices if the assigned Site has been changed.
          if _site_id is not None and self.site_id != _site_id:
              Device.objects.filter(rack=self).update(site_id=self.site.pk)
  
      def to_csv(self):
          return (
              self.site.name,
              self.group.name if self.group else None,
              self.name,
              self.facility_id,
              self.tenant.name if self.tenant else None,
              self.role.name if self.role else None,
              self.get_type_display() if self.type else None,
              self.serial,
              self.width,
              self.u_height,
              self.desc_units,
              self.comments,
          )
  
      @property
      def units(self):
          if self.desc_units:
              return range(1, self.u_height + 1)
          else:
              return reversed(range(1, self.u_height + 1))
  
      @property
      def display_name(self):
          if self.facility_id:
              return "{} ({})".format(self.name, self.facility_id)
          elif self.name:
              return self.name
          return ""
  
      def get_rack_units(self, face=RACK_FACE_FRONT, exclude=None, remove_redundant=False):
          """
          Return a list of rack units as dictionaries. Example: {'device': None, 'face': 0, 'id': 48, 'name': 'U48'}
          Each key 'device' is either a Device or None. By default, multi-U devices are repeated for each U they occupy.
  
          :param face: Rack face (front or rear)
          :param exclude: PK of a Device to exclude (optional); helpful when relocating a Device within a Rack
          :param remove_redundant: If True, rack units occupied by a device already listed will be omitted
          """
  
          elevation = OrderedDict()
          for u in self.units:
              elevation[u] = {'id': u, 'name': 'U{}'.format(u), 'face': face, 'device': None}
  
          # Add devices to rack units list
          if self.pk:
              for device in Device.objects.select_related('device_type__manufacturer', 'device_role')\
                      .annotate(devicebay_count=Count('device_bays'))\
                      .exclude(pk=exclude)\
                      .filter(rack=self, position__gt=0)\
                      .filter(Q(face=face) | Q(device_type__is_full_depth=True)):
                  if remove_redundant:
                      elevation[device.position]['device'] = device
                      for u in range(device.position + 1, device.position + device.device_type.u_height):
                          elevation.pop(u, None)
                  else:
                      for u in range(device.position, device.position + device.device_type.u_height):
                          elevation[u]['device'] = device
  
          return [u for u in elevation.values()]
  
      def get_front_elevation(self):
          return self.get_rack_units(face=RACK_FACE_FRONT, remove_redundant=True)
  
      def get_rear_elevation(self):
          return self.get_rack_units(face=RACK_FACE_REAR, remove_redundant=True)
  
      def get_available_units(self, u_height=1, rack_face=None, exclude=list()):
          """
          Return a list of units within the rack available to accommodate a device of a given U height (default 1).
          Optionally exclude one or more devices when calculating empty units (needed when moving a device from one
          position to another within a rack).
  
          :param u_height: Minimum number of contiguous free units required
          :param rack_face: The face of the rack (front or rear) required; 'None' if device is full depth
          :param exclude: List of devices IDs to exclude (useful when moving a device within a rack)
          """
  
          # Gather all devices which consume U space within the rack
          devices = self.devices.select_related('device_type').filter(position__gte=1).exclude(pk__in=exclude)
  
          # Initialize the rack unit skeleton
          units = list(range(1, self.u_height + 1))
  
          # Remove units consumed by installed devices
          for d in devices:
              if rack_face is None or d.face == rack_face or d.device_type.is_full_depth:
                  for u in range(d.position, d.position + d.device_type.u_height):
                      try:
                          units.remove(u)
                      except ValueError:
                          # Found overlapping devices in the rack!
                          pass
  
          # Remove units without enough space above them to accommodate a device of the specified height
          available_units = []
          for u in units:
              if set(range(u, u + u_height)).issubset(units):
                  available_units.append(u)
  
          return list(reversed(available_units))
  
      def get_reserved_units(self):
          """
          Return a dictionary mapping all reserved units within the rack to their reservation.
          """
          reserved_units = {}
          for r in self.reservations.all():
              for u in r.units:
                  reserved_units[u] = r
          return reserved_units
  
      def get_0u_devices(self):
          return self.devices.filter(position=0)
  
      def get_utilization(self):
          """
          Determine the utilization rate of the rack and return it as a percentage.
          """
          u_available = len(self.get_available_units())
          return int(float(self.u_height - u_available) / self.u_height * 100)
  
  
  @python_2_unicode_compatible
  class RackReservation(ChangeLoggedModel):
      """
      One or more reserved units within a Rack.
      """
      rack = models.ForeignKey(
          to='dcim.Rack',
          on_delete=models.CASCADE,
          related_name='reservations'
      )
      units = ArrayField(
          base_field=models.PositiveSmallIntegerField()
      )
      tenant = models.ForeignKey(
          to='tenancy.Tenant',
          on_delete=models.PROTECT,
          related_name='rackreservations',
          blank=True,
          null=True
      )
      user = models.ForeignKey(
          to=User,
          on_delete=models.PROTECT
      )
      description = models.CharField(
          max_length=100
      )
  
      class Meta:
          ordering = ['created']
  
      def __str__(self):
          return "Reservation for rack {}".format(self.rack)
  
      def clean(self):
  
          if self.units:
  
              # Validate that all specified units exist in the Rack.
              invalid_units = [u for u in self.units if u not in self.rack.units]
              if invalid_units:
                  raise ValidationError({
                      'units': "Invalid unit(s) for {}U rack: {}".format(
                          self.rack.u_height,
                          ', '.join([str(u) for u in invalid_units]),
                      ),
                  })
  
              # Check that none of the units has already been reserved for this Rack.
              reserved_units = []
              for resv in self.rack.reservations.exclude(pk=self.pk):
                  reserved_units += resv.units
              conflicting_units = [u for u in self.units if u in reserved_units]
              if conflicting_units:
                  raise ValidationError({
                      'units': 'The following units have already been reserved: {}'.format(
                          ', '.join([str(u) for u in conflicting_units]),
                      )
                  })
  
      @property
      def unit_list(self):
          """
          Express the assigned units as a string of summarized ranges. For example:
              [0, 1, 2, 10, 14, 15, 16] => "0-2, 10, 14-16"
          """
          group = (list(x) for _, x in groupby(sorted(self.units), lambda x, c=count(): next(c) - x))
          return ', '.join('-'.join(map(str, (g[0], g[-1])[:len(g)])) for g in group)
  
  
  #
  # Device Types
  #
  
  @python_2_unicode_compatible
  class Manufacturer(ChangeLoggedModel):
      """
      A Manufacturer represents a company which produces hardware devices; for example, Juniper or Dell.
      """
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
  
      csv_headers = ['name', 'slug']
  
      class Meta:
          ordering = ['name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return "{}?manufacturer={}".format(reverse('dcim:devicetype_list'), self.slug)
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
          )
  
  
  @python_2_unicode_compatible
  class DeviceType(ChangeLoggedModel, CustomFieldModel):
      """
      A DeviceType represents a particular make (Manufacturer) and model of device. It specifies rack height and depth, as
      well as high-level functional role(s).
  
      Each DeviceType can have an arbitrary number of component templates assigned to it, which define console, power, and
      interface objects. For example, a Juniper EX4300-48T DeviceType would have:
  
        * 1 ConsolePortTemplate
        * 2 PowerPortTemplates
        * 48 InterfaceTemplates
  
      When a new Device of this type is created, the appropriate console, power, and interface objects (as defined by the
      DeviceType) are automatically created as well.
      """
      manufacturer = models.ForeignKey(
          to='dcim.Manufacturer',
          on_delete=models.PROTECT,
          related_name='device_types'
      )
      model = models.CharField(
          max_length=50
      )
      slug = models.SlugField()
      part_number = models.CharField(
          max_length=50,
          blank=True,
          help_text='Discrete part number (optional)'
      )
      u_height = models.PositiveSmallIntegerField(
          default=1,
          verbose_name='Height (U)'
      )
      is_full_depth = models.BooleanField(
          default=True,
          verbose_name='Is full depth',
          help_text='Device consumes both front and rear rack faces'
      )
      interface_ordering = models.PositiveSmallIntegerField(
          choices=IFACE_ORDERING_CHOICES,
          default=IFACE_ORDERING_POSITION
      )
      is_console_server = models.BooleanField(
          default=False,
          verbose_name='Is a console server',
          help_text='This type of device has console server ports'
      )
      is_pdu = models.BooleanField(
          default=False,
          verbose_name='Is a PDU',
          help_text='This type of device has power outlets'
      )
      is_network_device = models.BooleanField(
          default=True,
          verbose_name='Is a network device',
          help_text='This type of device has network interfaces'
      )
      subdevice_role = models.NullBooleanField(
          default=None,
          verbose_name='Parent/child status',
          choices=SUBDEVICE_ROLE_CHOICES,
          help_text='Parent devices house child devices in device bays. Select '
                    '"None" if this device type is neither a parent nor a child.'
      )
      comments = models.TextField(
          blank=True
      )
      custom_field_values = GenericRelation(
          to='extras.CustomFieldValue',
          content_type_field='obj_type',
          object_id_field='obj_id'
      )
  
      tags = TaggableManager()
  
      csv_headers = [
          'manufacturer', 'model', 'slug', 'part_number', 'u_height', 'is_full_depth', 'is_console_server',
          'is_pdu', 'is_network_device', 'subdevice_role', 'interface_ordering', 'comments',
      ]
  
      class Meta:
          ordering = ['manufacturer', 'model']
          unique_together = [
              ['manufacturer', 'model'],
              ['manufacturer', 'slug'],
          ]
  
      def __str__(self):
          return self.model
  
      def __init__(self, *args, **kwargs):
          super(DeviceType, self).__init__(*args, **kwargs)
  
          # Save a copy of u_height for validation in clean()
          self._original_u_height = self.u_height
  
      def get_absolute_url(self):
          return reverse('dcim:devicetype', args=[self.pk])
  
      def to_csv(self):
          return (
              self.manufacturer.name,
              self.model,
              self.slug,
              self.part_number,
              self.u_height,
              self.is_full_depth,
              self.is_console_server,
              self.is_pdu,
              self.is_network_device,
              self.get_subdevice_role_display() if self.subdevice_role else None,
              self.get_interface_ordering_display(),
              self.comments,
          )
  
      def clean(self):
  
          # If editing an existing DeviceType to have a larger u_height, first validate that *all* instances of it have
          # room to expand within their racks. This validation will impose a very high performance penalty when there are
          # many instances to check, but increasing the u_height of a DeviceType should be a very rare occurrence.
          if self.pk is not None and self.u_height > self._original_u_height:
              for d in Device.objects.filter(device_type=self, position__isnull=False):
                  face_required = None if self.is_full_depth else d.face
                  u_available = d.rack.get_available_units(u_height=self.u_height, rack_face=face_required,
                                                           exclude=[d.pk])
                  if d.position not in u_available:
                      raise ValidationError({
                          'u_height': "Device {} in rack {} does not have sufficient space to accommodate a height of "
                                      "{}U".format(d, d.rack, self.u_height)
                      })
  
          if not self.is_console_server and self.cs_port_templates.count():
              raise ValidationError({
                  'is_console_server': "Must delete all console server port templates associated with this device before "
                                       "declassifying it as a console server."
              })
  
          if not self.is_pdu and self.power_outlet_templates.count():
              raise ValidationError({
                  'is_pdu': "Must delete all power outlet templates associated with this device before declassifying it "
                            "as a PDU."
              })
  
          if not self.is_network_device and self.interface_templates.filter(mgmt_only=False).count():
              raise ValidationError({
                  'is_network_device': "Must delete all non-management-only interface templates associated with this "
                                       "device before declassifying it as a network device."
              })
  
          if self.subdevice_role != SUBDEVICE_ROLE_PARENT and self.device_bay_templates.count():
              raise ValidationError({
                  'subdevice_role': "Must delete all device bay templates associated with this device before "
                                    "declassifying it as a parent device."
              })
  
          if self.u_height and self.subdevice_role == SUBDEVICE_ROLE_CHILD:
              raise ValidationError({
                  'u_height': "Child device types must be 0U."
              })
  
      @property
      def full_name(self):
          return '{} {}'.format(self.manufacturer.name, self.model)
  
      @property
      def is_parent_device(self):
          return bool(self.subdevice_role)
  
      @property
      def is_child_device(self):
          return bool(self.subdevice_role is False)
  
  
  @python_2_unicode_compatible
  class ConsolePortTemplate(ComponentModel):
      """
      A template for a ConsolePort to be created for a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='console_port_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  @python_2_unicode_compatible
  class ConsoleServerPortTemplate(ComponentModel):
      """
      A template for a ConsoleServerPort to be created for a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='cs_port_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  @python_2_unicode_compatible
  class PowerPortTemplate(ComponentModel):
      """
      A template for a PowerPort to be created for a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='power_port_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  @python_2_unicode_compatible
  class PowerOutletTemplate(ComponentModel):
      """
      A template for a PowerOutlet to be created for a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='power_outlet_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  @python_2_unicode_compatible
  class InterfaceTemplate(ComponentModel):
      """
      A template for a physical data interface on a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='interface_templates'
      )
      name = models.CharField(
          max_length=64
      )
      form_factor = models.PositiveSmallIntegerField(
          choices=IFACE_FF_CHOICES,
          default=IFACE_FF_10GE_SFP_PLUS
      )
      mgmt_only = models.BooleanField(
          default=False,
          verbose_name='Management only'
      )
  
      objects = InterfaceQuerySet.as_manager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  @python_2_unicode_compatible
  class DeviceBayTemplate(ComponentModel):
      """
      A template for a DeviceBay to be created for a new parent Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='device_bay_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
      def get_component_parent(self):
          return self.device_type
  
  
  #
  # Devices
  #
  
  @python_2_unicode_compatible
  class DeviceRole(ChangeLoggedModel):
      """
      Devices are organized by functional role; for example, "Core Switch" or "File Server". Each DeviceRole is assigned a
      color to be used when displaying rack elevations. The vm_role field determines whether the role is applicable to
      virtual machines as well.
      """
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
      color = ColorField()
      vm_role = models.BooleanField(
          default=True,
          verbose_name='VM Role',
          help_text='Virtual machines may be assigned to this role'
      )
  
      csv_headers = ['name', 'slug', 'color', 'vm_role']
  
      class Meta:
          ordering = ['name']
  
      def __str__(self):
          return self.name
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
              self.color,
              self.vm_role,
          )
  
  
  @python_2_unicode_compatible
  class Platform(ChangeLoggedModel):
      """
      Platform refers to the software or firmware running on a Device. For example, "Cisco IOS-XR" or "Juniper Junos".
      NetBox uses Platforms to determine how to interact with devices when pulling inventory data or other information by
      specifying a NAPALM driver.
      """
      name = models.CharField(
          max_length=50,
          unique=True
      )
      slug = models.SlugField(
          unique=True
      )
      manufacturer = models.ForeignKey(
          to='dcim.Manufacturer',
          on_delete=models.PROTECT,
          related_name='platforms',
          blank=True,
          null=True,
          help_text='Optionally limit this platform to devices of a certain manufacturer'
      )
      napalm_driver = models.CharField(
          max_length=50,
          blank=True,
          verbose_name='NAPALM driver',
          help_text='The name of the NAPALM driver to use when interacting with devices'
      )
      napalm_args = JSONField(
          blank=True,
          null=True,
          verbose_name='NAPALM arguments',
          help_text='Additional arguments to pass when initiating the NAPALM driver (JSON format)'
      )
      rpc_client = models.CharField(
          max_length=30,
          choices=RPC_CLIENT_CHOICES,
          blank=True,
          verbose_name='Legacy RPC client'
      )
  
      csv_headers = ['name', 'slug', 'manufacturer', 'napalm_driver', 'napalm_args']
  
      class Meta:
          ordering = ['name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return "{}?platform={}".format(reverse('dcim:device_list'), self.slug)
  
      def to_csv(self):
          return (
              self.name,
              self.slug,
              self.manufacturer.name if self.manufacturer else None,
              self.napalm_driver,
              self.napalm_args,
          )
  
  
  class DeviceManager(NaturalOrderByManager):
      natural_order_field = 'name'
  
  
  @python_2_unicode_compatible
  class Device(ChangeLoggedModel, ConfigContextModel, CustomFieldModel):
      """
      A Device represents a piece of physical hardware mounted within a Rack. Each Device is assigned a DeviceType,
      DeviceRole, and (optionally) a Platform. Device names are not required, however if one is set it must be unique.
  
      Each Device must be assigned to a site, and optionally to a rack within that site. Associating a device with a
      particular rack face or unit is optional (for example, vertically mounted PDUs do not consume rack units).
  
      When a new Device is created, console/power/interface/device bay components are created along with it as dictated
      by the component templates assigned to its DeviceType. Components can also be added, modified, or deleted after the
      creation of a Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.PROTECT,
          related_name='instances'
      )
      device_role = models.ForeignKey(
          to='dcim.DeviceRole',
          on_delete=models.PROTECT,
          related_name='devices'
      )
      tenant = models.ForeignKey(
          to='tenancy.Tenant',
          on_delete=models.PROTECT,
          related_name='devices',
          blank=True,
          null=True
      )
      platform = models.ForeignKey(
          to='dcim.Platform',
          on_delete=models.SET_NULL,
          related_name='devices',
          blank=True,
          null=True
      )
      name = NullableCharField(
          max_length=64,
          blank=True,
          null=True,
          unique=True
      )
      serial = models.CharField(
          max_length=50,
          blank=True,
          verbose_name='Serial number'
      )
      asset_tag = NullableCharField(
          max_length=50,
          blank=True,
          null=True,
          unique=True,
          verbose_name='Asset tag',
          help_text='A unique tag used to identify this device'
      )
      site = models.ForeignKey(
          to='dcim.Site',
          on_delete=models.PROTECT,
          related_name='devices'
      )
      rack = models.ForeignKey(
          to='dcim.Rack',
          on_delete=models.PROTECT,
          related_name='devices',
          blank=True,
          null=True
      )
      position = models.PositiveSmallIntegerField(
          blank=True,
          null=True,
          validators=[MinValueValidator(1)],
          verbose_name='Position (U)',
          help_text='The lowest-numbered unit occupied by the device'
      )
      face = models.PositiveSmallIntegerField(
          blank=True,
          null=True,
          choices=RACK_FACE_CHOICES,
          verbose_name='Rack face'
      )
      status = models.PositiveSmallIntegerField(
          choices=DEVICE_STATUS_CHOICES,
          default=DEVICE_STATUS_ACTIVE,
          verbose_name='Status'
      )
      primary_ip4 = models.OneToOneField(
          to='ipam.IPAddress',
          on_delete=models.SET_NULL,
          related_name='primary_ip4_for',
          blank=True,
          null=True,
          verbose_name='Primary IPv4'
      )
      primary_ip6 = models.OneToOneField(
          to='ipam.IPAddress',
          on_delete=models.SET_NULL,
          related_name='primary_ip6_for',
          blank=True,
          null=True,
          verbose_name='Primary IPv6'
      )
      cluster = models.ForeignKey(
          to='virtualization.Cluster',
          on_delete=models.SET_NULL,
          related_name='devices',
          blank=True,
          null=True
      )
      virtual_chassis = models.ForeignKey(
          to='VirtualChassis',
          on_delete=models.SET_NULL,
          related_name='members',
          blank=True,
          null=True
      )
      vc_position = models.PositiveSmallIntegerField(
          blank=True,
          null=True,
          validators=[MaxValueValidator(255)]
      )
      vc_priority = models.PositiveSmallIntegerField(
          blank=True,
          null=True,
          validators=[MaxValueValidator(255)]
      )
      comments = models.TextField(
          blank=True
      )
      custom_field_values = GenericRelation(
          to='extras.CustomFieldValue',
          content_type_field='obj_type',
          object_id_field='obj_id'
      )
      images = GenericRelation(
          to='extras.ImageAttachment'
      )
  
      objects = DeviceManager()
      tags = TaggableManager()
  
      csv_headers = [
          'name', 'device_role', 'tenant', 'manufacturer', 'model_name', 'platform', 'serial', 'asset_tag', 'status',
          'site', 'rack_group', 'rack_name', 'position', 'face', 'comments',
      ]
  
      class Meta:
          ordering = ['name']
          unique_together = [
              ['rack', 'position', 'face'],
              ['virtual_chassis', 'vc_position'],
          ]
          permissions = (
              ('napalm_read', 'Read-only access to devices via NAPALM'),
              ('napalm_write', 'Read/write access to devices via NAPALM'),
          )
  
      def __str__(self):
          return self.display_name or super(Device, self).__str__()
  
      def get_absolute_url(self):
          return reverse('dcim:device', args=[self.pk])
  
      def clean(self):
  
          # Validate site/rack combination
          if self.rack and self.site != self.rack.site:
              raise ValidationError({
                  'rack': "Rack {} does not belong to site {}.".format(self.rack, self.site),
              })
  
          if self.rack is None:
              if self.face is not None:
                  raise ValidationError({
                      'face': "Cannot select a rack face without assigning a rack.",
                  })
              if self.position:
                  raise ValidationError({
                      'face': "Cannot select a rack position without assigning a rack.",
                  })
  
          # Validate position/face combination
          if self.position and self.face is None:
              raise ValidationError({
                  'face': "Must specify rack face when defining rack position.",
              })
  
          # Prevent 0U devices from being assigned to a specific position
          if self.position and self.device_type.u_height == 0:
              raise ValidationError({
                  'position': "A U0 device type ({}) cannot be assigned to a rack position.".format(self.device_type)
              })
  
          if self.rack:
  
              try:
                  # Child devices cannot be assigned to a rack face/unit
                  if self.device_type.is_child_device and self.face is not None:
                      raise ValidationError({
                          'face': "Child device types cannot be assigned to a rack face. This is an attribute of the "
                                  "parent device."
                      })
                  if self.device_type.is_child_device and self.position:
                      raise ValidationError({
                          'position': "Child device types cannot be assigned to a rack position. This is an attribute of "
                                      "the parent device."
                      })
  
                  # Validate rack space
                  rack_face = self.face if not self.device_type.is_full_depth else None
                  exclude_list = [self.pk] if self.pk else []
                  try:
                      available_units = self.rack.get_available_units(
                          u_height=self.device_type.u_height, rack_face=rack_face, exclude=exclude_list
                      )
                      if self.position and self.position not in available_units:
                          raise ValidationError({
                              'position': "U{} is already occupied or does not have sufficient space to accommodate a(n) "
                                          "{} ({}U).".format(self.position, self.device_type, self.device_type.u_height)
                          })
                  except Rack.DoesNotExist:
                      pass
  
              except DeviceType.DoesNotExist:
                  pass
  
          # Validate primary IP addresses
          vc_interfaces = self.vc_interfaces.all()
          if self.primary_ip4:
              if self.primary_ip4.interface in vc_interfaces:
                  pass
              elif self.primary_ip4.nat_inside is not None and self.primary_ip4.nat_inside.interface in vc_interfaces:
                  pass
              else:
                  raise ValidationError({
                      'primary_ip4': "The specified IP address ({}) is not assigned to this device.".format(
                          self.primary_ip4),
                  })
          if self.primary_ip6:
              if self.primary_ip6.interface in vc_interfaces:
                  pass
              elif self.primary_ip6.nat_inside is not None and self.primary_ip6.nat_inside.interface in vc_interfaces:
                  pass
              else:
                  raise ValidationError({
                      'primary_ip6': "The specified IP address ({}) is not assigned to this device.".format(
                          self.primary_ip6),
                  })
  
          # Validate manufacturer/platform
          if self.device_type and self.platform:
              if self.platform.manufacturer and self.platform.manufacturer != self.device_type.manufacturer:
                  raise ValidationError({
                      'platform': "The assigned platform is limited to {} device types, but this device's type belongs "
                                  "to {}.".format(self.platform.manufacturer, self.device_type.manufacturer)
                  })
  
          # A Device can only be assigned to a Cluster in the same Site (or no Site)
          if self.cluster and self.cluster.site is not None and self.cluster.site != self.site:
              raise ValidationError({
                  'cluster': "The assigned cluster belongs to a different site ({})".format(self.cluster.site)
              })
  
          # Validate virtual chassis assignment
          if self.virtual_chassis and self.vc_position is None:
              raise ValidationError({
                  'vc_position': "A device assigned to a virtual chassis must have its position defined."
              })
  
      def save(self, *args, **kwargs):
  
          is_new = not bool(self.pk)
  
          super(Device, self).save(*args, **kwargs)
  
          # If this is a new Device, instantiate all of the related components per the DeviceType definition
          if is_new:
              ConsolePort.objects.bulk_create(
                  [ConsolePort(device=self, name=template.name) for template in
                   self.device_type.console_port_templates.all()]
              )
              ConsoleServerPort.objects.bulk_create(
                  [ConsoleServerPort(device=self, name=template.name) for template in
                   self.device_type.cs_port_templates.all()]
              )
              PowerPort.objects.bulk_create(
                  [PowerPort(device=self, name=template.name) for template in
                   self.device_type.power_port_templates.all()]
              )
              PowerOutlet.objects.bulk_create(
                  [PowerOutlet(device=self, name=template.name) for template in
                   self.device_type.power_outlet_templates.all()]
              )
              Interface.objects.bulk_create(
                  [Interface(device=self, name=template.name, form_factor=template.form_factor,
                             mgmt_only=template.mgmt_only) for template in self.device_type.interface_templates.all()]
              )
              DeviceBay.objects.bulk_create(
                  [DeviceBay(device=self, name=template.name) for template in
                   self.device_type.device_bay_templates.all()]
              )
  
          # Update Site and Rack assignment for any child Devices
          Device.objects.filter(parent_bay__device=self).update(site=self.site, rack=self.rack)
  
      def to_csv(self):
          return (
              self.name or '',
              self.device_role.name,
              self.tenant.name if self.tenant else None,
              self.device_type.manufacturer.name,
              self.device_type.model,
              self.platform.name if self.platform else None,
              self.serial,
              self.asset_tag,
              self.get_status_display(),
              self.site.name,
              self.rack.group.name if self.rack and self.rack.group else None,
              self.rack.name if self.rack else None,
              self.position,
              self.get_face_display(),
              self.comments,
          )
  
      @property
      def display_name(self):
          if self.name:
              return self.name
          elif self.virtual_chassis and self.virtual_chassis.master.name:
              return "{}:{}".format(self.virtual_chassis.master, self.vc_position)
          elif hasattr(self, 'device_type'):
              return "{}".format(self.device_type)
          return ""
  
      @property
      def identifier(self):
          """
          Return the device name if set; otherwise return the Device's primary key as {pk}
          """
          if self.name is not None:
              return self.name
          return '{{{}}}'.format(self.pk)
  
      @property
      def primary_ip(self):
          if settings.PREFER_IPV4 and self.primary_ip4:
              return self.primary_ip4
          elif self.primary_ip6:
              return self.primary_ip6
          elif self.primary_ip4:
              return self.primary_ip4
          else:
              return None
  
      def get_vc_master(self):
          """
          If this Device is a VirtualChassis member, return the VC master. Otherwise, return None.
          """
          return self.virtual_chassis.master if self.virtual_chassis else None
  
      @property
      def vc_interfaces(self):
          """
          Return a QuerySet matching all Interfaces assigned to this Device or, if this Device is a VC master, to another
          Device belonging to the same VirtualChassis.
          """
          filter = Q(device=self)
          if self.virtual_chassis and self.virtual_chassis.master == self:
              filter |= Q(device__virtual_chassis=self.virtual_chassis, mgmt_only=False)
          return Interface.objects.filter(filter)
  
      def get_children(self):
          """
          Return the set of child Devices installed in DeviceBays within this Device.
          """
          return Device.objects.filter(parent_bay__device=self.pk)
  
      def get_status_class(self):
          return STATUS_CLASSES[self.status]
  
      def get_rpc_client(self):
          """
          Return the appropriate RPC (e.g. NETCONF, ssh, etc.) client for this device's platform, if one is defined.
          """
          if not self.platform:
              return None
          return RPC_CLIENTS.get(self.platform.rpc_client)
  
  
  #
  # Console ports
  #
  
  @python_2_unicode_compatible
  class ConsolePort(ComponentModel):
      """
      A physical console port within a Device. ConsolePorts connect to ConsoleServerPorts.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='console_ports'
      )
      name = models.CharField(
          max_length=50
      )
      cs_port = models.OneToOneField(
          to='dcim.ConsoleServerPort',
          on_delete=models.SET_NULL,
          related_name='connected_console',
          verbose_name='Console server port',
          blank=True,
          null=True
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          default=CONNECTION_STATUS_CONNECTED
      )
  
      tags = TaggableManager()
  
      csv_headers = ['console_server', 'cs_port', 'device', 'console_port', 'connection_status']
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def to_csv(self):
          return (
              self.cs_port.device.identifier if self.cs_port else None,
              self.cs_port.name if self.cs_port else None,
              self.device.identifier,
              self.name,
              self.get_connection_status_display(),
          )
  
  
  #
  # Console server ports
  #
  
  class ConsoleServerPortManager(models.Manager):
  
      def get_queryset(self):
          # Pad any trailing digits to effect natural sorting
          return super(ConsoleServerPortManager, self).get_queryset().extra(select={
              'name_padded': r"CONCAT(REGEXP_REPLACE(dcim_consoleserverport.name, '\d+$', ''), "
                             r"LPAD(SUBSTRING(dcim_consoleserverport.name FROM '\d+$'), 8, '0'))",
          }).order_by('device', 'name_padded')
  
  
  @python_2_unicode_compatible
  class ConsoleServerPort(ComponentModel):
      """
      A physical port within a Device (typically a designated console server) which provides access to ConsolePorts.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='cs_ports'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = ConsoleServerPortManager()
      tags = TaggableManager()
  
      class Meta:
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def clean(self):
  
          # Check that the parent device's DeviceType is a console server
          if self.device is None:
              raise ValidationError("Console server ports must be assigned to devices.")
          device_type = self.device.device_type
          if not device_type.is_console_server:
              raise ValidationError("The {} {} device type does not support assignment of console server ports.".format(
                  device_type.manufacturer, device_type
              ))
  
  
  #
  # Power ports
  #
  
  @python_2_unicode_compatible
  class PowerPort(ComponentModel):
      """
      A physical power supply (intake) port within a Device. PowerPorts connect to PowerOutlets.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='power_ports'
      )
      name = models.CharField(
          max_length=50
      )
      power_outlet = models.OneToOneField(
          to='dcim.PowerOutlet',
          on_delete=models.SET_NULL,
          related_name='connected_port',
          blank=True,
          null=True
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          default=CONNECTION_STATUS_CONNECTED
      )
  
      tags = TaggableManager()
  
      csv_headers = ['pdu', 'power_outlet', 'device', 'power_port', 'connection_status']
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def to_csv(self):
          return (
              self.power_outlet.device.identifier if self.power_outlet else None,
              self.power_outlet.name if self.power_outlet else None,
              self.device.identifier,
              self.name,
              self.get_connection_status_display(),
          )
  
  
  #
  # Power outlets
  #
  
  class PowerOutletManager(models.Manager):
  
      def get_queryset(self):
          # Pad any trailing digits to effect natural sorting
          return super(PowerOutletManager, self).get_queryset().extra(select={
              'name_padded': r"CONCAT(REGEXP_REPLACE(dcim_poweroutlet.name, '\d+$', ''), "
                             r"LPAD(SUBSTRING(dcim_poweroutlet.name FROM '\d+$'), 8, '0'))",
          }).order_by('device', 'name_padded')
  
  
  @python_2_unicode_compatible
  class PowerOutlet(ComponentModel):
      """
      A physical power outlet (output) within a Device which provides power to a PowerPort.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='power_outlets'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = PowerOutletManager()
      tags = TaggableManager()
  
      class Meta:
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def clean(self):
  
          # Check that the parent device's DeviceType is a PDU
          if self.device is None:
              raise ValidationError("Power outlets must be assigned to devices.")
          device_type = self.device.device_type
          if not device_type.is_pdu:
              raise ValidationError("The {} {} device type does not support assignment of power outlets.".format(
                  device_type.manufacturer, device_type
              ))
  
  
  #
  # Interfaces
  #
  
  @python_2_unicode_compatible
  class Interface(ComponentModel):
      """
      A network interface within a Device or VirtualMachine. A physical Interface can connect to exactly one other
      Interface via the creation of an InterfaceConnection.
      """
      device = models.ForeignKey(
          to='Device',
          on_delete=models.CASCADE,
          related_name='interfaces',
          null=True,
          blank=True
      )
      virtual_machine = models.ForeignKey(
          to='virtualization.VirtualMachine',
          on_delete=models.CASCADE,
          related_name='interfaces',
          null=True,
          blank=True
      )
      lag = models.ForeignKey(
          to='self',
          on_delete=models.SET_NULL,
          related_name='member_interfaces',
          null=True,
          blank=True,
          verbose_name='Parent LAG'
      )
      name = models.CharField(
          max_length=64
      )
      form_factor = models.PositiveSmallIntegerField(
          choices=IFACE_FF_CHOICES,
          default=IFACE_FF_10GE_SFP_PLUS
      )
      enabled = models.BooleanField(
          default=True
      )
      mac_address = MACAddressField(
          null=True,
          blank=True,
          verbose_name='MAC Address'
      )
      mtu = models.PositiveSmallIntegerField(
          blank=True,
          null=True,
          verbose_name='MTU'
      )
      mgmt_only = models.BooleanField(
          default=False,
          verbose_name='OOB Management',
          help_text='This interface is used only for out-of-band management'
      )
      description = models.CharField(
          max_length=100,
          blank=True
      )
      mode = models.PositiveSmallIntegerField(
          choices=IFACE_MODE_CHOICES,
          blank=True,
          null=True
      )
      untagged_vlan = models.ForeignKey(
          to='ipam.VLAN',
          on_delete=models.SET_NULL,
          related_name='interfaces_as_untagged',
          null=True,
          blank=True,
          verbose_name='Untagged VLAN'
      )
      tagged_vlans = models.ManyToManyField(
          to='ipam.VLAN',
          related_name='interfaces_as_tagged',
          blank=True,
          verbose_name='Tagged VLANs'
      )
  
      objects = InterfaceQuerySet.as_manager()
      tags = TaggableManager()
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return reverse('dcim:interface', kwargs={'pk': self.pk})
  
      def get_component_parent(self):
          return self.device or self.virtual_machine
  
      def clean(self):
  
          # Check that the parent device's DeviceType is a network device
          if self.device is not None:
              device_type = self.device.device_type
              if not device_type.is_network_device:
                  raise ValidationError("The {} {} device type does not support assignment of network interfaces.".format(
                      device_type.manufacturer, device_type
                  ))
  
          # An Interface must belong to a Device *or* to a VirtualMachine
          if self.device and self.virtual_machine:
              raise ValidationError("An interface cannot belong to both a device and a virtual machine.")
          if not self.device and not self.virtual_machine:
              raise ValidationError("An interface must belong to either a device or a virtual machine.")
  
          # VM interfaces must be virtual
          if self.virtual_machine and self.form_factor is not IFACE_FF_VIRTUAL:
              raise ValidationError({
                  'form_factor': "Virtual machines can only have virtual interfaces."
              })
  
          # Virtual interfaces cannot be connected
          if self.form_factor in NONCONNECTABLE_IFACE_TYPES and self.is_connected:
              raise ValidationError({
                  'form_factor': "Virtual and wireless interfaces cannot be connected to another interface or circuit. "
                                 "Disconnect the interface or choose a suitable form factor."
              })
  
          # An interface's LAG must belong to the same device (or VC master)
          if self.lag and self.lag.device not in [self.device, self.device.get_vc_master()]:
              raise ValidationError({
                  'lag': "The selected LAG interface ({}) belongs to a different device ({}).".format(
                      self.lag.name, self.lag.device.name
                  )
              })
  
          # A virtual interface cannot have a parent LAG
          if self.form_factor in NONCONNECTABLE_IFACE_TYPES and self.lag is not None:
              raise ValidationError({
                  'lag': "{} interfaces cannot have a parent LAG interface.".format(self.get_form_factor_display())
              })
  
          # Only a LAG can have LAG members
          if self.form_factor != IFACE_FF_LAG and self.member_interfaces.exists():
              raise ValidationError({
                  'form_factor': "Cannot change interface form factor; it has LAG members ({}).".format(
                      ", ".join([iface.name for iface in self.member_interfaces.all()])
                  )
              })
  
          # Validate untagged VLAN
          if self.untagged_vlan and self.untagged_vlan.site not in [self.parent.site, None]:
              raise ValidationError({
                  'untagged_vlan': "The untagged VLAN ({}) must belong to the same site as the interface's parent "
                                   "device/VM, or it must be global".format(self.untagged_vlan)
              })
  
      def save(self, *args, **kwargs):
  
          # Remove untagged VLAN assignment for non-802.1Q interfaces
          if self.mode is None:
              self.untagged_vlan = None
  
          # Only "tagged" interfaces may have tagged VLANs assigned. ("tagged all" implies all VLANs are assigned.)
          if self.pk and self.mode is not IFACE_MODE_TAGGED:
              self.tagged_vlans.clear()
  
          return super(Interface, self).save(*args, **kwargs)
  
      def log_change(self, user, request_id, action):
          """
          Include the connected Interface (if any).
          """
  
          # It's possible that an Interface can be deleted _after_ its parent Device/VM, in which case trying to resolve
          # the component parent will raise DoesNotExist. For more discussion, see
          # https://github.com/digitalocean/netbox/issues/2323
          try:
              parent_obj = self.get_component_parent()
          except ObjectDoesNotExist:
              parent_obj = None
  
          ObjectChange(
              user=user,
              request_id=request_id,
              changed_object=self,
              related_object=parent_obj,
              action=action,
              object_data=serialize_object(self, extra={
                  'connected_interface': self.connected_interface.pk if self.connection else None,
                  'connection_status': self.connection.connection_status if self.connection else None,
              })
          ).save()
  
      # TODO: Replace `parent` with get_component_parent() (from ComponentModel)
      @property
      def parent(self):
          return self.device or self.virtual_machine
  
      @property
      def is_connectable(self):
          return self.form_factor not in NONCONNECTABLE_IFACE_TYPES
  
      @property
      def is_virtual(self):
          return self.form_factor in VIRTUAL_IFACE_TYPES
  
      @property
      def is_wireless(self):
          return self.form_factor in WIRELESS_IFACE_TYPES
  
      @property
      def is_lag(self):
          return self.form_factor == IFACE_FF_LAG
  
      @property
      def is_connected(self):
          try:
              return bool(self.circuit_termination)
          except ObjectDoesNotExist:
              pass
          return bool(self.connection)
  
      @property
      def connection(self):
          try:
              return self.connected_as_a
          except ObjectDoesNotExist:
              pass
          try:
              return self.connected_as_b
          except ObjectDoesNotExist:
              pass
          return None
  
      @property
      def connected_interface(self):
          try:
              if self.connected_as_a:
                  return self.connected_as_a.interface_b
          except ObjectDoesNotExist:
              pass
          try:
              if self.connected_as_b:
                  return self.connected_as_b.interface_a
          except ObjectDoesNotExist:
              pass
          return None
  
  
  class InterfaceConnection(models.Model):
      """
      An InterfaceConnection represents a symmetrical, one-to-one connection between two Interfaces. There is no
      significant difference between the interface_a and interface_b fields.
      """
      interface_a = models.OneToOneField(
          to='dcim.Interface',
          on_delete=models.CASCADE,
          related_name='connected_as_a'
      )
      interface_b = models.OneToOneField(
          to='dcim.Interface',
          on_delete=models.CASCADE,
          related_name='connected_as_b'
      )
      connection_status = models.BooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          default=CONNECTION_STATUS_CONNECTED,
          verbose_name='Status'
      )
  
      csv_headers = ['device_a', 'interface_a', 'device_b', 'interface_b', 'connection_status']
  
      def clean(self):
          try:
              if self.interface_a == self.interface_b:
                  raise ValidationError({
                      'interface_b': "Cannot connect an interface to itself."
                  })
              if self.interface_a.form_factor in NONCONNECTABLE_IFACE_TYPES:
                  raise ValidationError({
                      'interface_a': '{} is not a connectable interface type.'.format(
                          self.interface_a.get_form_factor_display()
                      )
                  })
              if self.interface_b.form_factor in NONCONNECTABLE_IFACE_TYPES:
                  raise ValidationError({
                      'interface_b': '{} is not a connectable interface type.'.format(
                          self.interface_b.get_form_factor_display()
                      )
                  })
          except ObjectDoesNotExist:
              pass
  
      def to_csv(self):
          return (
              self.interface_a.device.identifier,
              self.interface_a.name,
              self.interface_b.device.identifier,
              self.interface_b.name,
              self.get_connection_status_display(),
          )
  
      def log_change(self, user, request_id, action):
          """
          Create a new ObjectChange for each of the two affected Interfaces.
          """
          interfaces = (
              (self.interface_a, self.interface_b),
              (self.interface_b, self.interface_a),
          )
          for interface, peer_interface in interfaces:
              if action == OBJECTCHANGE_ACTION_DELETE:
                  connection_data = {
                      'connected_interface': None,
                  }
              else:
                  connection_data = {
                      'connected_interface': peer_interface.pk,
                      'connection_status': self.connection_status
                  }
              ObjectChange(
                  user=user,
                  request_id=request_id,
                  changed_object=interface,
                  related_object=interface.parent,
                  action=OBJECTCHANGE_ACTION_UPDATE,
                  object_data=serialize_object(interface, extra=connection_data)
              ).save()
  
  
  #
  # Device bays
  #
  
  @python_2_unicode_compatible
  class DeviceBay(ComponentModel):
      """
      An empty space within a Device which can house a child device
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='device_bays'
      )
      name = models.CharField(
          max_length=50,
          verbose_name='Name'
      )
      installed_device = models.OneToOneField(
          to='dcim.Device',
          on_delete=models.SET_NULL,
          related_name='parent_bay',
          blank=True,
          null=True
      )
  
      tags = TaggableManager()
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = ['device', 'name']
  
      def __str__(self):
          return '{} - {}'.format(self.device.name, self.name)
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def clean(self):
  
          # Validate that the parent Device can have DeviceBays
          if not self.device.device_type.is_parent_device:
              raise ValidationError("This type of device ({}) does not support device bays.".format(
                  self.device.device_type
              ))
  
          # Cannot install a device into itself, obviously
          if self.device == self.installed_device:
              raise ValidationError("Cannot install a device into itself.")
  
  
  #
  # Inventory items
  #
  
  @python_2_unicode_compatible
  class InventoryItem(ComponentModel):
      """
      An InventoryItem represents a serialized piece of hardware within a Device, such as a line card or power supply.
      InventoryItems are used only for inventory purposes.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='inventory_items'
      )
      parent = models.ForeignKey(
          to='self',
          on_delete=models.CASCADE,
          related_name='child_items',
          blank=True,
          null=True
      )
      name = models.CharField(
          max_length=50,
          verbose_name='Name'
      )
      manufacturer = models.ForeignKey(
          to='dcim.Manufacturer',
          on_delete=models.PROTECT,
          related_name='inventory_items',
          blank=True,
          null=True
      )
      part_id = models.CharField(
          max_length=50,
          verbose_name='Part ID',
          blank=True
      )
      serial = models.CharField(
          max_length=50,
          verbose_name='Serial number',
          blank=True
      )
      asset_tag = NullableCharField(
          max_length=50,
          unique=True,
          blank=True,
          null=True,
          verbose_name='Asset tag',
          help_text='A unique tag used to identify this item'
      )
      discovered = models.BooleanField(
          default=False,
          verbose_name='Discovered'
      )
      description = models.CharField(
          max_length=100,
          blank=True
      )
  
      tags = TaggableManager()
  
      csv_headers = [
          'device', 'name', 'manufacturer', 'part_id', 'serial', 'asset_tag', 'discovered', 'description',
      ]
  
      class Meta:
          ordering = ['device__id', 'parent__id', 'name']
          unique_together = ['device', 'parent', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def get_component_parent(self):
          return self.device
  
      def to_csv(self):
          return (
              self.device.name or '{' + self.device.pk + '}',
              self.name,
              self.manufacturer.name if self.manufacturer else None,
              self.part_id,
              self.serial,
              self.asset_tag,
              self.discovered,
              self.description,
          )
  
  
  #
  # Virtual chassis
  #
  
  @python_2_unicode_compatible
  class VirtualChassis(ChangeLoggedModel):
      """
      A collection of Devices which operate with a shared control plane (e.g. a switch stack).
      """
      master = models.OneToOneField(
          to='Device',
          on_delete=models.PROTECT,
          related_name='vc_master_for'
      )
      domain = models.CharField(
          max_length=30,
          blank=True
      )
  
      tags = TaggableManager()
  
      csv_headers = ['master', 'domain']
  
      class Meta:
          ordering = ['master']
          verbose_name_plural = 'virtual chassis'
  
      def __str__(self):
          return str(self.master) if hasattr(self, 'master') else 'New Virtual Chassis'
  
      def get_absolute_url(self):
          return self.master.get_absolute_url()
  
      def clean(self):
  
          # Verify that the selected master device has been assigned to this VirtualChassis. (Skip when creating a new
          # VirtualChassis.)
          if self.pk and self.master not in self.members.all():
              raise ValidationError({
                  'master': "The selected master is not assigned to this virtual chassis."
              })
  
      def to_csv(self):
          return (
              self.master,
              self.domain,
          )
  