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# Devices and Cabling

## Devices

Every piece of hardware which is installed within a site or rack exists in Nautobot as a device. Devices are measured in rack units (U) and can be half depth or full depth. A device may have a height of 0U: These devices do not consume vertical rack space and cannot be assigned to a particular rack unit. A common example of a 0U device is a vertically-mounted PDU.

When assigning a multi-U device to a rack, it is considered to be mounted in the lowest-numbered rack unit which it occupies. For example, a 3U device which occupies U8 through U10 is said to be mounted in U8. This logic applies to racks with both ascending and descending unit numbering.

A device is said to be full-depth if its installation on one rack face prevents the installation of any other device on the opposite face within the same rack unit(s). This could be either because the device is physically too deep to allow a device behind it, or because the installation of an opposing device would impede airflow.

Each device must be instantiated from a pre-created device type, and its default components (console ports, power ports, interfaces, etc.) will be created automatically. (The device type associated with a device may be changed after its creation, however its components will not be updated retroactively.)

Each device must be assigned a site, device role, and operational `status`, and may optionally be assigned to a specific location and/or rack within a site. A platform, serial number, and asset tag may optionally be assigned to each device.

Device names must be unique within a site, unless the device has been assigned to a tenant. Devices may also be unnamed.

When a device has one or more interfaces with IP addresses assigned, a primary IP for the device can be designated, for both IPv4 and IPv6.

For Devices forming a group (Failover, Load-Sharing, Redundacy or similar) refer to Device Redundancy Groups model documentation.

### Developer API

The `Device` Django model class supports a method called `create_components()`. This method is normally called during `device_instance.save()`, which is called whenever you save create a Device via the GUI or the REST API, but if you are working directly in the ORM and encounter one of the two following scenarios, `device_instance.save()` is not called:

- Usage of `device_instance.objects.bulk_create()` to perform a bulk creation of Device objects
- Usage of `device_instance.save()` during handling of the `nautobot_database_ready` signal (which uses historical models)

In these cases you will have to manually run `device_instance.create_components()` in order to instantiate the device type's component templates (interfaces, power ports, etc.).

## Device Roles

Devices can be organized by functional roles, which are fully customizable by the user. For example, you might create roles for core switches, distribution switches, and access switches within your network.

## Platforms

A platform defines the type of software running on a device or virtual machine. This can be helpful to model when it is necessary to distinguish between different versions or feature sets. Note that two devices of the same type may be assigned different platforms: For example, one Juniper MX240 might run Junos 14 while another runs Junos 15.

Platforms may optionally be limited by manufacturer: If a platform is assigned to a particular manufacturer, it can only be assigned to devices with a type belonging to that manufacturer.

The platform model can be used to indicate which "network driver" Nautobot (and Jobs, Apps, etc.) should use when connecting to a remote device running this platform. This is a generic string corresponding loosely to a Netmiko driver name. As there are many different libraries and applications for connecting to a device, rather than having a separate model field for each such connection type, Nautobot uses netutils to translate the generic network driver string into a variety of library-specific driver strings (Ansible "collection name", PyATS "OS" value, Scrapli "platform", etc.) which can be accessed via the UI, REST API, and GraphQL as needed. An administrator can extend or override the default translations provided by netutils by configuring the `NETWORK_DRIVERS` dictionary appropriately. (If your extensions are generally applicable, please consider making a pull request against netutils to update the package!)

Added in version 1.6.0

The `network_driver` database field and the `network_driver_mappings` derived property were added to the Platform data model. Support for the `NETWORK_DRIVERS` setting was added.

For historical reasons, the NAPALM driver (`napalm_driver` field) and any associated arguments (`napalm_args` field) Nautobot should use when connecting to a remote device via NAPALM can (and must) be configured directly rather than being derived from the network driver. The name of the NAPALM driver along with optional parameters are stored with the platform.

Apps and Jobs should transition to using the `network_driver_mappings["napalm"]` property when connecting to a device via NAPALM. Nautobot may deprecate the use of the `napalm_driver` and `napalm_args` fields in a future release.

The assignment of platforms to devices is an optional feature, and may be disregarded if not desired.

## Device Components

Added in version 1.4.5

The fields `created` and `last_updated` were added to all device component models. If you upgraded from Nautobot 1.4.4 or earlier, the values for these fields will default to `None` (null).

### Console Ports

A console port provides connectivity to the physical console of a device. These are typically used for temporary access by someone who is physically near the device, or for remote out-of-band access provided via a networked console server. Each console port may be assigned a physical type.

Cables can connect console ports to console server ports or pass-through ports.

### Console Server Ports

A console server is a device which provides remote access to the local consoles of connected devices. They are typically used to provide remote out-of-band access to network devices. Each console server port may be assigned a physical type.

Cables can connect console server ports to console ports or pass-through ports.

### Power Ports

A power port represents the inlet of a device where it draws its power, i.e. the connection port(s) on a device's power supply. Each power port may be assigned a physical type, as well as allocated and maximum draw values (in watts). These values can be used to calculate the overall utilization of an upstream power feed.

Info

When creating a power port on a device which supplies power to downstream devices, the allocated and maximum draw numbers should be left blank. Utilization will be calculated by taking the sum of all power ports of devices connected downstream.

Cables can connect power ports only to power outlets or power feeds. (Pass-through ports cannot be used to model power distribution.)

### Power Outlets

Power outlets represent the outlets on a power distribution unit (PDU) or other device that supply power to dependent devices. Each power port may be assigned a physical type, and may be associated with a specific feed leg (where three-phase power is used) and/or a specific upstream power port. This association can be used to model the distribution of power within a device.

For example, imagine a PDU with one power port which draws from a three-phase feed and 48 power outlets arranged into three banks of 16 outlets each. Outlets 1-16 would be associated with leg A on the port, and outlets 17-32 and 33-48 would be associated with legs B and C, respectively.

Cables can connect power outlets only to downstream power ports. (Pass-through ports cannot be used to model power distribution.)

### Interfaces

Interfaces in Nautobot represent network interfaces used to exchange data with connected devices. On modern networks, these are most commonly Ethernet, but other types are supported as well. Each interface must be assigned a type, an operational `status` and may optionally be assigned a MAC address, MTU, and IEEE 802.1Q mode (tagged or access). Each interface can also be enabled or disabled, and optionally designated as management-only (for out-of-band management).

The following operational statuses are available by default:

- Planned
- Maintenance
- Active
- Decommissioning
- Failed

Added in version 1.4.0

- Added `bridge` field.
- Added `parent_interface` field.
- Added `status` field.

Interfaces may be physical or virtual in nature, but only physical interfaces may be connected via cables. Cables can connect interfaces to pass-through ports, circuit terminations, or other interfaces.

Physical interfaces may be arranged into a link aggregation group (LAG) and associated with a parent LAG (virtual) interface. LAG interfaces can be recursively nested to model bonding of trunk groups. Like all virtual interfaces, LAG interfaces cannot be connected physically.

IP addresses can be assigned to interfaces. VLANs can also be assigned to each interface as either tagged or untagged. (An interface may have only one untagged VLAN.)

Note

Although devices and virtual machines both can have interfaces, a separate model is used for each. Thus, device interfaces have some properties that are not present on virtual machine interfaces and vice versa.

Added in version 1.6.0

Interfaces can now be assigned to an Interface Redundancy Group to represent redundancy protocols such as HSRP or VRRP.

### Front Ports

Front ports are pass-through ports used to represent physical cable connections that comprise part of a longer path. For example, the ports on the front face of a UTP patch panel would be modeled in Nautobot as front ports. Each port is assigned a physical type, and must be mapped to a specific rear port on the same device. A single rear port may be mapped to multiple rear ports, using numeric positions to annotate the specific alignment of each.

### Rear Ports

Like front ports, rear ports are pass-through ports which represent the continuation of a path from one cable to the next. Each rear port is defined with its physical type and a number of positions: Rear ports with more than one position can be mapped to multiple front ports. This can be useful for modeling instances where multiple paths share a common cable (for example, six discrete two-strand fiber connections sharing a 12-strand MPO cable).

Note

Front and rear ports need not necessarily reside on the actual front or rear device face. This terminology is used primarily to distinguish between the two components in a pass-through port pairing.

### Device Bays

Device bays represent a space or slot within a parent device in which a child device may be installed. For example, a 2U parent chassis might house four individual blade servers. The chassis would appear in the rack elevation as a 2U device with four device bays, and each server within it would be defined as a 0U device installed in one of the device bays. Child devices do not appear within rack elevations or count as consuming rack units.

Child devices are first-class Devices in their own right: That is, they are fully independent managed entities which don't share any control plane with the parent. Just like normal devices, child devices have their own platform (OS), role, tags, and components. LAG interfaces may not group interfaces belonging to different child devices.

Note

Device bays are not suitable for modeling line cards (such as those commonly found in chassis-based routers and switches), as these components depend on the control plane of the parent device to operate. Instead, line cards and similarly non-autonomous hardware should be modeled as inventory items within a device, with any associated interfaces or other components assigned directly to the device.

### Inventory Items

Inventory items represent hardware components installed within a device, such as a power supply or CPU or line card. Inventory items are distinct from other device components in that they cannot be templatized on a device type, and cannot be connected by cables. They are intended to be used primarily for inventory purposes.

Each inventory item can be assigned a manufacturer, part ID, serial number, and asset tag (all optional). A boolean toggle is also provided to indicate whether each item was entered manually or discovered automatically (by some process outside of Nautobot).

Inventory items are hierarchical in nature, such that any individual item may be designated as the parent for other items. For example, an inventory item might be created to represent a line card which houses several SFP optics, each of which exists as a child item within the device.

## Virtual Chassis

A virtual chassis represents a set of devices which share a common control plane. A common example of this is a stack of switches which are connected and configured to operate as a single device. A virtual chassis must be assigned a name and may be assigned a domain.

Each device in the virtual chassis is referred to as a VC member, and assigned a position and (optionally) a priority. VC member devices commonly reside within the same rack, though this is not a requirement. One of the devices may be designated as the VC master: This device will typically be assigned a name, services, and other attributes related to managing the VC.

Note

It's important to recognize the distinction between a virtual chassis and a chassis-based device. A virtual chassis is not suitable for modeling a chassis-based switch with removable line cards (such as the Juniper EX9208), as its line cards are not physically autonomous devices.

## Cables

All connections between device components in Nautobot are represented using cables. A cable represents a direct physical connection between two termination points, such as between a console port and a patch panel port, or between two network interfaces.

Each cable must have two endpoints defined. These endpoints are sometimes referenced as A and B for clarity, however cables are direction-agnostic and the order in which terminations are made has no meaning. Cables may be connected to the following objects:

- Circuit terminations
- Console ports
- Console server ports
- Interfaces
- Pass-through ports (front and rear)
- Power feeds
- Power outlets
- Power ports

Each cable may be assigned a type, label, length, and color. Each cable must also assigned to an operational `status`. The following statuses are available by default:

- Active
- Planned
- Decommissioning

### Tracing Cables

A cable may be traced from either of its endpoints by clicking the "trace" button. (A REST API endpoint also provides this functionality.) Nautobot will follow the path of connected cables from this termination across the directly connected cable to the far-end termination. If the cable connects to a pass-through port, and the peer port has another cable connected, Nautobot will continue following the cable path until it encounters a non-pass-through or unconnected termination point. The entire path will be displayed to the user.

In the example below, three individual cables comprise a path between devices A and D:

Traced from Interface 1 on Device A, Nautobot will show the following path:

- Cable 1: Interface 1 to Front Port 1
- Cable 2: Rear Port 1 to Rear Port 2
- Cable 3: Front Port 2 to Interface 2

A cable can also be traced through a circuit.

Traced from Interface 1 on Device A, Nautobot will show the following path:

- Cable 1: Interface 1 to Side A
- Cable 2: Side Z to Interface 2