text: 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 GenericForeignKey, GenericRelation
  from django.contrib.contenttypes.models import ContentType
  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
  from django.urls import reverse
  from mptt.models import MPTTModel, TreeForeignKey
  from taggit.managers import TaggableManager
  from timezone_field import TimeZoneField
  
  from extras.models import ConfigContextModel, CustomFieldModel, ObjectChange
  from utilities.fields import ColorField, NullableCharField
  from utilities.managers import NaturalOrderingManager
  from utilities.models import ChangeLoggedModel
  from utilities.utils import serialize_object, to_meters
  from .constants import *
  from .exceptions import LoopDetected
  from .fields import ASNField, MACAddressField
  from .managers import DeviceComponentManager, InterfaceManager
  
  
  class ComponentTemplateModel(models.Model):
  
      class Meta:
          abstract = True
  
      def log_change(self, user, request_id, action):
          """
          Log an ObjectChange including the parent DeviceType.
          """
          ObjectChange(
              user=user,
              request_id=request_id,
              changed_object=self,
              related_object=self.device_type,
              action=action,
              object_data=serialize_object(self)
          ).save()
  
  
  class ComponentModel(models.Model):
  
      class Meta:
          abstract = True
  
      def log_change(self, user, request_id, action):
          """
          Log an ObjectChange including the parent Device/VM.
          """
          parent = self.device if self.device is not None else getattr(self, 'virtual_machine', None)
          ObjectChange(
              user=user,
              request_id=request_id,
              changed_object=self,
              related_object=parent,
              action=action,
              object_data=serialize_object(self)
          ).save()
  
  
  class CableTermination(models.Model):
      cable = models.ForeignKey(
          to='dcim.Cable',
          on_delete=models.SET_NULL,
          related_name='+',
          blank=True,
          null=True
      )
  
      # Generic relations to Cable. These ensure that an attached Cable is deleted if the terminated object is deleted.
      _cabled_as_a = GenericRelation(
          to='dcim.Cable',
          content_type_field='termination_a_type',
          object_id_field='termination_a_id'
      )
      _cabled_as_b = GenericRelation(
          to='dcim.Cable',
          content_type_field='termination_b_type',
          object_id_field='termination_b_id'
      )
  
      class Meta:
          abstract = True
  
      def trace(self, position=1, follow_circuits=False, cable_history=None):
          """
          Return a list representing a complete cable path, with each individual segment represented as a three-tuple:
              [
                  (termination A, cable, termination B),
                  (termination C, cable, termination D),
                  (termination E, cable, termination F)
              ]
          """
          def get_peer_port(termination, position=1, follow_circuits=False):
              from circuits.models import CircuitTermination
  
              # Map a front port to its corresponding rear port
              if isinstance(termination, FrontPort):
                  return termination.rear_port, termination.rear_port_position
  
              # Map a rear port/position to its corresponding front port
              elif isinstance(termination, RearPort):
                  if position not in range(1, termination.positions + 1):
                      raise Exception("Invalid position for {} ({} positions): {})".format(
                          termination, termination.positions, position
                      ))
                  try:
                      peer_port = FrontPort.objects.get(
                          rear_port=termination,
                          rear_port_position=position,
                      )
                      return peer_port, 1
                  except ObjectDoesNotExist:
                      return None, None
  
              # Follow a circuit to its other termination
              elif isinstance(termination, CircuitTermination) and follow_circuits:
                  peer_termination = termination.get_peer_termination()
                  if peer_termination is None:
                      return None, None
                  return peer_termination, position
  
              # Termination is not a pass-through port
              else:
                  return None, None
  
          if not self.cable:
              return [(self, None, None)]
  
          # Record cable history to detect loops
          if cable_history is None:
              cable_history = []
          elif self.cable in cable_history:
              raise LoopDetected()
          cable_history.append(self.cable)
  
          far_end = self.cable.termination_b if self.cable.termination_a == self else self.cable.termination_a
          path = [(self, self.cable, far_end)]
  
          peer_port, position = get_peer_port(far_end, position, follow_circuits)
          if peer_port is None:
              return path
  
          try:
              next_segment = peer_port.trace(position, follow_circuits, cable_history)
          except LoopDetected:
              return path
  
          if next_segment is None:
              return path + [(peer_port, None, None)]
  
          return path + next_segment
  
  
  #
  # Regions
  #
  
  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,
          )
  
      @property
      def site_count(self):
          return Site.objects.filter(
              Q(region=self) |
              Q(region__in=self.get_descendants())
          ).count()
  
  
  #
  # Sites
  #
  
  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 = NaturalOrderingManager()
      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):
          from circuits.models import Circuit
          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
  #
  
  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,
          )
  
  
  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 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
      )
      status = models.PositiveSmallIntegerField(
          choices=RACK_STATUS_CHOICES,
          default=RACK_STATUS_ACTIVE
      )
      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'
      )
      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 rack'
      )
      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'
      )
      outer_width = models.PositiveSmallIntegerField(
          blank=True,
          null=True
      )
      outer_depth = models.PositiveSmallIntegerField(
          blank=True,
          null=True
      )
      outer_unit = models.PositiveSmallIntegerField(
          choices=RACK_DIMENSION_UNIT_CHOICES,
          blank=True,
          null=True
      )
      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 = NaturalOrderingManager()
      tags = TaggableManager()
  
      csv_headers = [
          'site', 'group_name', 'name', 'facility_id', 'tenant', 'status', 'role', 'type', 'serial', 'asset_tag', 'width',
          'u_height', 'desc_units', 'outer_width', 'outer_depth', 'outer_unit', 'comments',
      ]
  
      class Meta:
          ordering = ['site', 'group', 'name']
          unique_together = [
              ['group', 'name'],
              ['group', 'facility_id'],
          ]
  
      def __str__(self):
          return self.display_name or super().__str__()
  
      def get_absolute_url(self):
          return reverse('dcim:rack', args=[self.pk])
  
      def clean(self):
  
          # Validate outer dimensions and unit
          if (self.outer_width is not None or self.outer_depth is not None) and self.outer_unit is None:
              raise ValidationError("Must specify a unit when setting an outer width/depth")
          elif self.outer_width is None and self.outer_depth is None:
              self.outer_unit = None
  
          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().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.get_status_display(),
              self.role.name if self.role else None,
              self.get_type_display() if self.type else None,
              self.serial,
              self.asset_tag,
              self.width,
              self.u_height,
              self.desc_units,
              self.outer_width,
              self.outer_depth,
              self.outer_unit,
              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_status_class(self):
          return STATUS_CLASSES[self.status]
  
      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)
  
  
  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
  #
  
  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,
          )
  
  
  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'
      )
      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', 'subdevice_role', 'comments',
      ]
  
      class Meta:
          ordering = ['manufacturer', 'model']
          unique_together = [
              ['manufacturer', 'model'],
              ['manufacturer', 'slug'],
          ]
  
      def __str__(self):
          return self.model
  
      def __init__(self, *args, **kwargs):
          super().__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.get_subdevice_role_display() if self.subdevice_role else None,
              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 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)
  
  
  class ConsolePortTemplate(ComponentTemplateModel):
      """
      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='consoleport_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class ConsoleServerPortTemplate(ComponentTemplateModel):
      """
      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='consoleserverport_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class PowerPortTemplate(ComponentTemplateModel):
      """
      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='powerport_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class PowerOutletTemplate(ComponentTemplateModel):
      """
      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='poweroutlet_templates'
      )
      name = models.CharField(
          max_length=50
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class InterfaceTemplate(ComponentTemplateModel):
      """
      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 = InterfaceManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class FrontPortTemplate(ComponentTemplateModel):
      """
      Template for a pass-through port on the front of a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='frontport_templates'
      )
      name = models.CharField(
          max_length=64
      )
      type = models.PositiveSmallIntegerField(
          choices=PORT_TYPE_CHOICES
      )
      rear_port = models.ForeignKey(
          to='dcim.RearPortTemplate',
          on_delete=models.CASCADE,
          related_name='frontport_templates'
      )
      rear_port_position = models.PositiveSmallIntegerField(
          default=1,
          validators=[MinValueValidator(1), MaxValueValidator(64)]
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = [
              ['device_type', 'name'],
              ['rear_port', 'rear_port_position'],
          ]
  
      def __str__(self):
          return self.name
  
      def clean(self):
  
          # Validate rear port assignment
          if self.rear_port.device_type != self.device_type:
              raise ValidationError(
                  "Rear port ({}) must belong to the same device type".format(self.rear_port)
              )
  
          # Validate rear port position assignment
          if self.rear_port_position > self.rear_port.positions:
              raise ValidationError(
                  "Invalid rear port position ({}); rear port {} has only {} positions".format(
                      self.rear_port_position, self.rear_port.name, self.rear_port.positions
                  )
              )
  
  
  class RearPortTemplate(ComponentTemplateModel):
      """
      Template for a pass-through port on the rear of a new Device.
      """
      device_type = models.ForeignKey(
          to='dcim.DeviceType',
          on_delete=models.CASCADE,
          related_name='rearport_templates'
      )
      name = models.CharField(
          max_length=64
      )
      type = models.PositiveSmallIntegerField(
          choices=PORT_TYPE_CHOICES
      )
      positions = models.PositiveSmallIntegerField(
          default=1,
          validators=[MinValueValidator(1), MaxValueValidator(64)]
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  class DeviceBayTemplate(ComponentTemplateModel):
      """
      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
      )
  
      objects = DeviceComponentManager()
  
      class Meta:
          ordering = ['device_type', 'name']
          unique_together = ['device_type', 'name']
  
      def __str__(self):
          return self.name
  
  
  #
  # Devices
  #
  
  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,
          )
  
  
  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)'
      )
  
      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 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 = NaturalOrderingManager()
      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().__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 hasattr(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().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.consoleport_templates.all()]
              )
              ConsoleServerPort.objects.bulk_create(
                  [ConsoleServerPort(device=self, name=template.name) for template in
                   self.device_type.consoleserverport_templates.all()]
              )
              PowerPort.objects.bulk_create(
                  [PowerPort(device=self, name=template.name) for template in
                   self.device_type.powerport_templates.all()]
              )
              PowerOutlet.objects.bulk_create(
                  [PowerOutlet(device=self, name=template.name) for template in
                   self.device_type.poweroutlet_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()]
              )
              RearPort.objects.bulk_create([
                  RearPort(
                      device=self,
                      name=template.name,
                      type=template.type,
                      positions=template.positions
                  ) for template in self.device_type.rearport_templates.all()
              ])
              FrontPort.objects.bulk_create([
                  FrontPort(
                      device=self,
                      name=template.name,
                      type=template.type,
                      rear_port=RearPort.objects.get(device=self, name=template.rear_port.name),
                      rear_port_position=template.rear_port_position,
                  ) for template in self.device_type.frontport_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]
  
  
  #
  # Console ports
  #
  
  class ConsolePort(CableTermination, ComponentModel):
      """
      A physical console port within a Device. ConsolePorts connect to ConsoleServerPorts.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='consoleports'
      )
      name = models.CharField(
          max_length=50
      )
      connected_endpoint = models.OneToOneField(
          to='dcim.ConsoleServerPort',
          on_delete=models.SET_NULL,
          related_name='connected_endpoint',
          blank=True,
          null=True
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name']
  
      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 to_csv(self):
          return (
              self.device.identifier,
              self.name,
          )
  
  
  #
  # Console server ports
  #
  
  class ConsoleServerPort(CableTermination, 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='consoleserverports'
      )
      name = models.CharField(
          max_length=50
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name']
  
      class Meta:
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def to_csv(self):
          return (
              self.device.identifier,
              self.name,
          )
  
  
  #
  # Power ports
  #
  
  class PowerPort(CableTermination, 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='powerports'
      )
      name = models.CharField(
          max_length=50
      )
      connected_endpoint = models.OneToOneField(
          to='dcim.PowerOutlet',
          on_delete=models.SET_NULL,
          related_name='connected_endpoint',
          blank=True,
          null=True
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name']
  
      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 to_csv(self):
          return (
              self.device.identifier,
              self.name,
          )
  
  
  #
  # Power outlets
  #
  
  class PowerOutlet(CableTermination, 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='poweroutlets'
      )
      name = models.CharField(
          max_length=50
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name']
  
      class Meta:
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def get_absolute_url(self):
          return self.device.get_absolute_url()
  
      def to_csv(self):
          return (
              self.device.identifier,
              self.name,
          )
  
  
  #
  # Interfaces
  #
  
  class Interface(CableTermination, ComponentModel):
      """
      A network interface within a Device or VirtualMachine. A physical Interface can connect to exactly one other
      Interface.
      """
      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
      )
      name = models.CharField(
          max_length=64
      )
      _connected_interface = models.OneToOneField(
          to='self',
          on_delete=models.SET_NULL,
          related_name='+',
          blank=True,
          null=True
      )
      _connected_circuittermination = models.OneToOneField(
          to='circuits.CircuitTermination',
          on_delete=models.SET_NULL,
          related_name='+',
          blank=True,
          null=True
      )
      connection_status = models.NullBooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          blank=True
      )
      lag = models.ForeignKey(
          to='self',
          on_delete=models.SET_NULL,
          related_name='member_interfaces',
          null=True,
          blank=True,
          verbose_name='Parent LAG'
      )
      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.PositiveIntegerField(
          blank=True,
          null=True,
          validators=[MinValueValidator(1), MaxValueValidator(65536)],
          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 = InterfaceManager()
      tags = TaggableManager()
  
      csv_headers = [
          'device', 'virtual_machine', 'name', 'lag', 'form_factor', 'enabled', 'mac_address', 'mtu', 'mgmt_only',
          'description', 'mode',
      ]
  
      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 to_csv(self):
          return (
              self.device.identifier if self.device else None,
              self.virtual_machine.name if self.virtual_machine else None,
              self.name,
              self.lag.name if self.lag else None,
              self.get_form_factor_display(),
              self.enabled,
              self.mac_address,
              self.mtu,
              self.mgmt_only,
              self.description,
              self.get_mode_display(),
          )
  
      def clean(self):
  
          # 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.cable or getattr(self, 'circuit_termination', False)
          ):
              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().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.device or self.virtual_machine
          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)
          ).save()
  
      @property
      def connected_endpoint(self):
          if self._connected_interface:
              return self._connected_interface
          return self._connected_circuittermination
  
      @connected_endpoint.setter
      def connected_endpoint(self, value):
          from circuits.models import CircuitTermination
  
          if value is None:
              self._connected_interface = None
              self._connected_circuittermination = None
          elif isinstance(value, Interface):
              self._connected_interface = value
              self._connected_circuittermination = None
          elif isinstance(value, CircuitTermination):
              self._connected_interface = None
              self._connected_circuittermination = value
          else:
              raise ValueError(
                  "Connected endpoint must be an Interface or CircuitTermination, not {}.".format(type(value))
              )
  
      @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 count_ipaddresses(self):
          return self.ip_addresses.count()
  
  
  #
  # Pass-through ports
  #
  
  class FrontPort(CableTermination, ComponentModel):
      """
      A pass-through port on the front of a Device.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='frontports'
      )
      name = models.CharField(
          max_length=64
      )
      type = models.PositiveSmallIntegerField(
          choices=PORT_TYPE_CHOICES
      )
      rear_port = models.ForeignKey(
          to='dcim.RearPort',
          on_delete=models.CASCADE,
          related_name='frontports'
      )
      rear_port_position = models.PositiveSmallIntegerField(
          default=1,
          validators=[MinValueValidator(1), MaxValueValidator(64)]
      )
      description = models.CharField(
          max_length=100,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name', 'type', 'rear_port', 'rear_port_position', 'description']
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = [
              ['device', 'name'],
              ['rear_port', 'rear_port_position'],
          ]
  
      def __str__(self):
          return self.name
  
      def to_csv(self):
          return (
              self.device.identifier,
              self.name,
              self.get_type_display(),
              self.rear_port.name,
              self.rear_port_position,
              self.description,
          )
  
      def clean(self):
  
          # Validate rear port assignment
          if self.rear_port.device != self.device:
              raise ValidationError(
                  "Rear port ({}) must belong to the same device".format(self.rear_port)
              )
  
          # Validate rear port position assignment
          if self.rear_port_position > self.rear_port.positions:
              raise ValidationError(
                  "Invalid rear port position ({}); rear port {} has only {} positions".format(
                      self.rear_port_position, self.rear_port.name, self.rear_port.positions
                  )
              )
  
  
  class RearPort(CableTermination, ComponentModel):
      """
      A pass-through port on the rear of a Device.
      """
      device = models.ForeignKey(
          to='dcim.Device',
          on_delete=models.CASCADE,
          related_name='rearports'
      )
      name = models.CharField(
          max_length=64
      )
      type = models.PositiveSmallIntegerField(
          choices=PORT_TYPE_CHOICES
      )
      positions = models.PositiveSmallIntegerField(
          default=1,
          validators=[MinValueValidator(1), MaxValueValidator(64)]
      )
      description = models.CharField(
          max_length=100,
          blank=True
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name', 'type', 'positions', 'description']
  
      class Meta:
          ordering = ['device', 'name']
          unique_together = ['device', 'name']
  
      def __str__(self):
          return self.name
  
      def to_csv(self):
          return (
              self.device.identifier,
              self.name,
              self.get_type_display(),
              self.positions,
              self.description,
          )
  
  
  #
  # Device bays
  #
  
  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
      )
  
      objects = DeviceComponentManager()
      tags = TaggableManager()
  
      csv_headers = ['device', 'name', 'installed_device']
  
      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 to_csv(self):
          return (
              self.device.identifier,
              self.name,
              self.installed_device.identifier if self.installed_device else None,
          )
  
      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
  #
  
  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 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
  #
  
  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,
          )
  
  
  #
  # Cables
  #
  
  class Cable(ChangeLoggedModel):
      """
      A physical connection between two endpoints.
      """
      termination_a_type = models.ForeignKey(
          to=ContentType,
          limit_choices_to={'model__in': CABLE_TERMINATION_TYPES},
          on_delete=models.PROTECT,
          related_name='+'
      )
      termination_a_id = models.PositiveIntegerField()
      termination_a = GenericForeignKey(
          ct_field='termination_a_type',
          fk_field='termination_a_id'
      )
      termination_b_type = models.ForeignKey(
          to=ContentType,
          limit_choices_to={'model__in': CABLE_TERMINATION_TYPES},
          on_delete=models.PROTECT,
          related_name='+'
      )
      termination_b_id = models.PositiveIntegerField()
      termination_b = GenericForeignKey(
          ct_field='termination_b_type',
          fk_field='termination_b_id'
      )
      type = models.PositiveSmallIntegerField(
          choices=CABLE_TYPE_CHOICES,
          blank=True,
          null=True
      )
      status = models.BooleanField(
          choices=CONNECTION_STATUS_CHOICES,
          default=CONNECTION_STATUS_CONNECTED
      )
      label = models.CharField(
          max_length=100,
          blank=True
      )
      color = ColorField(
          blank=True
      )
      length = models.PositiveSmallIntegerField(
          blank=True,
          null=True
      )
      length_unit = models.PositiveSmallIntegerField(
          choices=CABLE_LENGTH_UNIT_CHOICES,
          blank=True,
          null=True
      )
      # Stores the normalized length (in meters) for database ordering
      _abs_length = models.DecimalField(
          max_digits=10,
          decimal_places=4,
          blank=True,
          null=True
      )
  
      csv_headers = [
          'termination_a_type', 'termination_a_id', 'termination_b_type', 'termination_b_id', 'type', 'status', 'label',
          'color', 'length', 'length_unit',
      ]
  
      class Meta:
          ordering = ['pk']
          unique_together = (
              ('termination_a_type', 'termination_a_id'),
              ('termination_b_type', 'termination_b_id'),
          )
  
      def __init__(self, *args, **kwargs):
  
          super().__init__(*args, **kwargs)
  
          # Create an ID string for use by __str__(). We have to save a copy of pk since it's nullified after .delete()
          # is called.
          self.id_string = '#{}'.format(self.pk)
  
      def __str__(self):
          return self.label or self.id_string
  
      def get_absolute_url(self):
          return reverse('dcim:cable', args=[self.pk])
  
      def clean(self):
  
          # Check that termination types are compatible
          type_a = self.termination_a_type.model
          type_b = self.termination_b_type.model
          if type_b not in COMPATIBLE_TERMINATION_TYPES.get(type_a):
              raise ValidationError("Incompatible termination types: {} and {}".format(
                  self.termination_a_type, self.termination_b_type
              ))
  
          # A termination point cannot be connected to itself
          if self.termination_a == self.termination_b:
              raise ValidationError("Cannot connect {} to itself".format(self.termination_a_type))
  
          # A front port cannot be connected to its corresponding rear port
          if (
              type_a in ['frontport', 'rearport'] and
              type_b in ['frontport', 'rearport'] and
              (
                  getattr(self.termination_a, 'rear_port', None) == self.termination_b or
                  getattr(self.termination_b, 'rear_port', None) == self.termination_a
              )
          ):
              raise ValidationError("A front port cannot be connected to it corresponding rear port")
  
          # Check for an existing Cable connected to either termination object
          if self.termination_a.cable not in (None, self):
              raise ValidationError("{} already has a cable attached (#{})".format(
                  self.termination_a, self.termination_a.cable_id
              ))
          if self.termination_b.cable not in (None, self):
              raise ValidationError("{} already has a cable attached (#{})".format(
                  self.termination_b, self.termination_b.cable_id
              ))
  
          # Virtual interfaces cannot be connected
          endpoint_a, endpoint_b, _ = self.get_path_endpoints()
          if (
              (
                  isinstance(endpoint_a, Interface) and
                  endpoint_a.form_factor == IFACE_FF_VIRTUAL
              ) or
              (
                  isinstance(endpoint_b, Interface) and
                  endpoint_b.form_factor == IFACE_FF_VIRTUAL
              )
          ):
              raise ValidationError("Cannot connect to a virtual interface")
  
          # Validate length and length_unit
          if self.length is not None and self.length_unit is None:
              raise ValidationError("Must specify a unit when setting a cable length")
          elif self.length is None:
              self.length_unit = None
  
      def save(self, *args, **kwargs):
  
          # Store the given length (if any) in meters for use in database ordering
          if self.length and self.length_unit:
              self._abs_length = to_meters(self.length, self.length_unit)
  
          super().save(*args, **kwargs)
  
      def to_csv(self):
          return (
              '{}.{}'.format(self.termination_a_type.app_label, self.termination_a_type.model),
              self.termination_a_id,
              '{}.{}'.format(self.termination_b_type.app_label, self.termination_b_type.model),
              self.termination_b_id,
              self.get_type_display(),
              self.get_status_display(),
              self.label,
              self.color,
              self.length,
              self.length_unit,
          )
  
      def get_path_endpoints(self):
          """
          Traverse both ends of a cable path and return its connected endpoints. Note that one or both endpoints may be
          None.
          """
          a_path = self.termination_b.trace()
          b_path = self.termination_a.trace()
  
          # Determine overall path status (connected or planned)
          if self.status == CONNECTION_STATUS_PLANNED:
              path_status = CONNECTION_STATUS_PLANNED
          else:
              path_status = CONNECTION_STATUS_CONNECTED
              for segment in a_path[1:] + b_path[1:]:
                  if segment[1] is None or segment[1].status == CONNECTION_STATUS_PLANNED:
                      path_status = CONNECTION_STATUS_PLANNED
                      break
  
          a_endpoint = a_path[-1][2]
          b_endpoint = b_path[-1][2]
  
          return a_endpoint, b_endpoint, path_status
  