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# Circuits

## Providers

A circuit provider is any entity which provides some form of connectivity of among sites or organizations within a site. While this obviously includes carriers which offer Internet and private transit service, it might also include Internet exchange (IX) points and even organizations with whom you peer directly. Each circuit within Nautobot must be assigned a provider and a circuit ID which is unique to that provider.

Each provider may be assigned an autonomous system number (ASN), an account number, and contact information.

## Provider Network

Added in version 1.3.0

A provider network represents an abstract portion of network topology, just like in a topology diagram. For example, a provider network may be used to represent a provider's MPLS network.

Each provider network must be assigned to a provider. A circuit may terminate to either a provider network or to a site.

## Circuits

A communications circuit represents a single physical link connecting exactly two endpoints, commonly referred to as its A and Z terminations. A circuit in Nautobot may have zero, one, or two terminations defined. It is common to have only one termination defined when you don't necessarily care about the details of the provider side of the circuit, e.g. for Internet access circuits. Both terminations would likely be modeled for circuits which connect one customer site to another.

Each circuit is associated with a provider and a user-defined type. For example, you might have Internet access circuits delivered to each site by one provider, and private MPLS circuits delivered by another. Each circuit must be assigned a circuit ID, each of which must be unique per provider.

Each circuit must be assigned to a `status`. The following statuses are available by default:

- Planned
- Provisioning
- Active
- Offline
- Deprovisioning
- Decommissioned

Circuits also have optional fields for annotating their installation date and commit rate, and may be assigned to Nautobot tenants.

Note

Nautobot currently models only physical circuits: those which have exactly two endpoints. It is common to layer virtualized constructs (virtual circuits) such as MPLS or EVPN tunnels on top of these, however Nautobot does not yet support virtual circuit modeling.

## Circuit Types

Circuits are classified by functional type. These types are completely customizable, and are typically used to convey the type of service being delivered over a circuit. For example, you might define circuit types for:

- Internet transit
- Out-of-band connectivity
- Peering
- Private backhaul

## Circuit Terminations

The association of a circuit with a particular site, location, and/or device is modeled separately as a circuit termination. A circuit may have up to two terminations, labeled A and Z. A single-termination circuit can be used when you don't know (or care) about the far end of a circuit (for example, an Internet access circuit which connects to a transit provider). A dual-termination circuit is useful for tracking circuits which connect two sites.

Each circuit termination is attached to either a site (and optionally also a location within the site) or a provider network. Site terminations may optionally be connected via a cable to a specific device interface or port within that site. Each termination must be assigned a port speed, and can optionally be assigned an upstream speed if it differs from the downstream speed (a common scenario with e.g. DOCSIS cable modems). Fields are also available to track cross-connect and patch panel details.

In adherence with Nautobot's philosophy of closely modeling the real world, a circuit may be connected only to a physical interface. For example, circuits may not terminate to LAG interfaces, which are virtual in nature. In such cases, a separate physical circuit is associated with each LAG member interface and each needs to be modeled discretely.

Note

A circuit in Nautobot represents a physical link, and cannot have more than two endpoints. When modeling a multi-point topology, each leg of the topology must be defined as a discrete circuit, with one end terminating within the provider's infrastructure. The provider network model is ideal for representing these networks.