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YANG Models for Network Topologies

This blog post discusses different YANG models for describing network topologies. There are multiple applications for a topology data model. For example, nodes within the network can use a data model to capture their understanding of the overall network topology and expose it to a network controller. A network controller can then use the instantiated topology data to compare and reconcile its own view of the network topology with that of the network elements it controls. A network controller might even use the data model to expose its view of the topology it controls to applications via northbound APIs.

YANG Model Use Cases

The Architecture for the Interface to the Routing System allows for a mechanism where the distributed control plane can be augmented by an outside control plane through an open, accessible interface. The IETF’s I2RS working group summarized the use cases in this document. One of the use cases being to (a) provide a coherent view of the network topology from the collected data, (b) present the topology view to applications that need to understand the topology, and (c) use topology information to improve application-specific mechanisms, such as path selection, resources reservation, etc.

Just before the IETF 101 meeting in London, some important RFCs were published by the IETF in the Network Management domain. Here, we review three of them.

  • RFC 8342, Network Management Datastore Architecture (NMDA)
  • RFC 8345, A YANG Data Model for Network Topologies
  • RFC 8346, A YANG Data Model for Layer 3 Topologies

Network Management Datastore Architecture (NMDA)

Datastores are a fundamental concept binding data models written in the YANG data modeling language to network management protocols, such as the Network Configuration Protocol (NETCONF) and RESTCONF. RFC 8342 defines an architectural framework for datastores that addresses requirements that were not well supported in an earlier, simpler model.

Agreement on a common architectural model for datastores ensures that data models can be written in a way that is agnostic to the encoding used by network management protocols. The architectural framework identifies a set of conceptual datastores, but it does not mandate that all network management protocols expose all these conceptual datastores.

A YANG Data Model for Network Topologies

RFC 8345 defines an abstract (base) YANG data model to represent networks and topologies. The data model is divided into two parts:

The first part enables the definition of network hierarchies or network stacks (i.e., networks that are layered on top of each other) and maintenance of an inventory of nodes contained in a network.

The second part of the data model augments the basic network data model with information to describe topology. Specifically, it adds the concepts of “links” and “termination points” to describe how nodes in a network are connected to each other.

The data model also introduces vertical layering relationships between networks that can be augmented to cover both network inventories and network/service topologies.

A YANG Data Model for Layer 3 Topologies

RFC 8346 introduces a YANG data model for Layer 3 (L3) network topologies, specifically L3 Unicast. The model gives applications a holistic view of the topology of a L3 network, all contained in a single conceptual YANG datastore. The data model builds on and augments the data model for network topologies defined in RFC 8345.

The document also defines an example model that covers OSPF.

As a co-author of YANG models for network topology and L3 topologies, Packet Design is enabling and embracing the Software Defined Networking revolution. Some of our customers have already embraced SDN in their production networks.