Internet-Draft | IS-IS Topology YANG | June 2024 |
Dios, et al. | Expires 6 December 2024 | [Page] |
This document defines a YANG data model for representing an abstracted view of a network topology that contains Intermediate System to Intermediate System (IS-IS). This document augments the 'ietf-network' and 'ietf-network-topology' data models by adding IS-IS concepts and explains how the data model can be used to represent the IS-IS topology.¶
The YANG data model defined in this document conforms to the Network Management Datastore Architecture (NMDA).¶
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Network operators perform the capacity planning for their networks and run regular what-if scenarios analysis based on representations of the real network. Those what-if analysis and capacity planning processes require, among other information, a topological view (domains, nodes, links, network interconnection) of the deployed network.¶
This document defines a YANG data model representing an abstracted view of a network topology containing Intermediate System to Intermediate System (IS-IS). It covers the topology of IP/MPLS networks running IS-IS as Interior Gateway Protocol (IGP) protocol. The proposed YANG model augments the "A YANG Data Model for Network Topologies" [RFC8345] and "A YANG Data Model for Layer 3 Topologies" [RFC8346] by adding IS-IS concepts. It is worth to highlight that the Yang model can also be used together with [RFC8795] and [I-D.draft-ietf-teas-yang-l3-te-topo] when Traffic engineering characteristics are required in the topological view.¶
This YANG data model can be used to export the IS-IS related topology directly from a network controller to Operation Support System (OSS) tools or to a higher level controller.¶
Note that the YANG model is in this document strictly adheres to the concepts (and the YANG module) in "A YANG Data Model for Network Topologies" [RFC8345] and"A YANG Data Model for Layer 3 Topologies" [RFC8346]. While investigating the IS-IS topology, some limitations have discovered in [RFC8345], regarding how the digital map can be represented. Those limitations (and potential improvements) are covered in [I-D.draft-havel-opsawg-digital-map].¶
This document explains the scope and purpose of the IS-IS topology model and how the topology and service models fit together. The YANG data model defined in this document conforms to the Network Management Datastore Architecture [RFC8342].¶
This document assumes that the reader is familiar with IS-IS and the contents of [RFC8345]. The document uses terms from those documents.¶
The terminology for describing YANG data models is found in [RFC7950], [RFC8795] and [RFC8346].¶
The term Digital Twin, Digital Map, Digital Map Modelling, Digital Map Model, Digital Map Data, and Topology are specified in [I-D.draft-havel-opsawg-digital-map].¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119], [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Authors include a simplified graphical representation of the data model specified in Section 5 of this document. The meaning of the symbols in these diagrams is defined in [RFC8340].¶
In this document, names of data nodes and other data model objects are prefixed using the standard prefix associated with the corresponding YANG imported modules, as shown in the following table.¶
Prefix | Yang Module | Reference |
---|---|---|
isisnt | ietf-l3-isis-topology | RFCXXX |
yang | ietf-yang-types | [RFC6991] |
RFC Editor Note: Please replace XXXX with the RFC number assigned to this document. Please remove this note.¶
This information is required in the IP/MPLS planning process to properly assess the required network resources to meet the traffic demands in normal and failure scenarios. Network operators perform the capacity planning for their networks and run regular what-if scenarios analysis based on representations of the real network. Those what-if analysis and capacity planning processes require, among other information, a topological view (domains, nodes, links, network interconnection) of the deployed network.¶
The standardization of an abstracted view of the IS-IS topology model as NorthBound Interface (NBI) of Software Defined Networking (SDN) controllers allows the unified query of the IS-IS topology in order to inject this information into third party tools covering specialized cases.¶
The IS-IS topological model should export enough IS-IS information to permit these tools to simulate the IP routing. By mapping the traffic demand, ideally at the IP flow level, to the topology, we can simulate the traffic growth, evaluating this way its effect on the routing and quality of service. That is, simulating how IP-level traffic demands would be forwarded, after IS-IS convergence is reached, and from there estimating, using appropriate mathematical models, related KPIs like the occupation in the links or end-to-end latencies.¶
In summary, the network-wide view of the IS-IS topology enables multiple use cases:¶
Network design: verifying that the actual deployed IS-IS network conforms to the planned design.¶
Capacity planning. Dimensioning or redesign of the IP infrastructure to satisfy target KPI metrics under existing or forecasted traffic demands.¶
What-if analysis. Estimation of the network KPIs in modified network situations. For instance, failure situations, traffic anomaly situations, addition or deletion of new adjacencies, IGP weight reconfigurations, etc.¶
Failure analysis. Systematic and massive test of the network under multiple simulated failure situations, evaluating the network fault tolerance properties, and using mathematical models to derive statistical network availability metrics.¶
[RFC9130] specifies a YANG data model that can be used to configure and manage the IS-IS protocol on network elements. This data model covers the configuration of an IS-IS routing protocol instance, as well as the retrieval of IS-IS operational states. [RFC9130] is still expected to be used for individual network elements configuration and monitoring. On the other hand, the proposed YANG model in this document covers the abstracted view of the entire network topology containing IS-IS. As such, this model is aimed at being available via the NBI of an SDN controller.¶
As described in [I-D.draft-havel-opsawg-digital-map], the Digital Map provides the core multi-layer topology model and data for the digital twin and connects them to the other digital twin models and data.¶
The Digital Map Modelling defines the core topological entities, their role in the network, core properties, and relationships both inside each layer and between the layers.¶
The Digital Map Model is a basic topological model that is linked to other functional parts of the digital twin and connects them all: configuration, maintenance, assurance (KPIs, status, health, symptoms), Traffic Engineering (TE), different behaviors and actions, simulation, emulation, mathematical abstractions, AI algorithms, etc.¶
As such the IGP topology of the Digital Map (in this case, IS-IS) is just one of the layers of the Digital Map, for specific user (the network operator in charge of the IGP) for specific IGP use cases as described before.¶
IP/MPLS networks can contain multiple domain IGP domains. We can define an IGP domain as the collection of nodes and links that participate in the same IGP process. The topology information of a domain can be structured according to ietf-network-topology data model [RFC8345]. For example, if BGP-LS [RFC9552] is used to collect the information, the nodes and links that are announced with the same combination of AS number / domain ID are considered to belong to the same domain.¶
If a node and/or layer termination point participates in more than one IGP, it will be present in multiple IGP domain networks. As the basic components, node/links/termination points [RFC8345], it is therefore possible to joint the different different IGP topologies from a digital map modeling point of view. The ietf-network instance MUST include the following properties to indicate it is a domain running an IGP instance:¶
A network-id that uniquely identifies such domain in the network. The "network-types" property should include the l3t:l3-unicast-topology, to indicate it is a network in which the nodes are capable of forwarding unicast packet. Also, this draft proposed to add a new property, "isis-topology", to indicate the topology being represented is running the IS-IS IGP process.¶
Also, should the topology include information such as bandwidth, delay information or color, it must include the "YANG Data Model for Traffic Engineering" [RFC8795] te-topology YANG data model. To include delay and bandwdith performance measurements , MUST include tet-pkt:te-packet under the previous property The supporting-network property can include the network-id of a base layer-3 network. The node property should include the list of nodes as described below. The ietf-network-topology:link MUST be present, with one link per each IP adjacency (one link for each direction of the adjancency).¶
The abstract (base) network data model is defined in the "ietf-network" and "ietf-network-topology" modules of [RFC8345]. The L3 topology module is defined in the "ietf-l3-unicast-topology" module of [RFC8346]. The ietf-l3-isis-topology builds on the data models defined in [RFC8345] and [RFC8346], augmenting the nodes with IS-IS information.¶
There is a set of parameters and augmentations that are included at the node level. Each parameter and description are detailed following:¶
Network-types: Its presence identifies the IS-IS topology type. Thus, the network type MUST be isis-topology.¶
IS-IS timer attributes: Identifies the node timer attributes configured in the network element. They are LSP lifetime and the LSP refresh interval.¶
IS-IS status: contains the IS-IS status attributes (level, area-address and neighbours).¶
The following figure is based on the Figure 1 from [RFC8346], where the example-ospf-topology is replaced with ietf-l3-isis-topology and where arrows show how the modules augment each other.¶
There is a set of parameters and augmentations that are included at the network level.¶
Network-types: Its presence identifies the IS-IS topology type. Thus, the network type MUST be isis-topology.¶
There is a set of parameters and augmentations that are included at the node level. Each parameter and description are detailed following:¶
IS-IS node core attributes: contains the IS-IS core attributes (system-id, level, area-address).¶
IS-IS timer attributes: Identifies the node timer attributes configured in the network element. They are LSP lifetime and the LSP refresh interval.¶
There is a set of parameters and augmentations that are included at the link level. Each parameter and description are detailed following:¶
IS-IS link level. The level must be the same as the termination points at each end for Level 1 and Level 2 interfaces. There may be 2 links between the Level1-2 IS-IS interfaces, one for Level 1 adjacency and one for Level 2 adjacency.¶
IS-IS link metric. Added on top of metric1 and metric2 of the l3-link-attributes¶
There is a set of parameters and augmentations are included at the termination point level. Each parameter is listed as follows:¶
There are some limitations in the [RFC8345] that are explained in more detail in [I-D.draft-havel-opsawg-digital-map]. The current version of the ietf-l3-isis-topology module is based on the current version of [RFC8345]. The following will be addressed when [RFC8345] is extended to support the identified limitations:¶
Figure 2 below shows the tree diagram of the YANG data model defined in module ietf-l3-isis-topology.yang (Figure 3).¶
This module imports types from [RFC8343] and [RFC8345]. Following the YANG model is presented.¶
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF {!RFC6241}} or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶
The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶
There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations.¶
This document registers the following namespace URIs in the IETF XML registry [RFC3688]:¶
-------------------------------------------------------------------- URI: urn:ietf:params:xml:ns:yang:ietf-l3-isis-topology Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace. --------------------------------------------------------------------¶
This document registers the following YANG module in the YANG Module Names registry [RFC6020]:¶
-------------------------------------------------------------------- name: ietf-l3-isis-topology namespace: urn:ietf:params:xml:ns:yang:ietf-l3-isis-topology maintained by IANA: N prefix: ietf-l3-isis-topology reference: RFC XXXX --------------------------------------------------------------------¶
Note to the RFC-Editor: Please remove this section before publishing.¶
The Yang based topology model proposed in this draft is being used today in one of the Telefonica operations to export the Multi-vendor IP/MPLS topology based on multiple IS-IS domains to several Operation Support System tools for visualization, capacity planning and simulation. A commercial controller has implemented the exposure of the information. It is one of the building blocks to expose the network capabilities, together with other models which cover the inventory and service provisioning in a vendor-agnostic fashion.¶
As mentioned in [I-D.draft-havel-opsawg-digital-map], a Digital Map PoC with a real lab has been built, based on multi- vendor devices, with [RFC8345] as the base YANG module for the topology building blocks. This PoC successfully modelled IS-IS routing (among other technologies and layers), but it needs to be further aligned with this latest developments in this draft.¶
E-lighthouse Network Solutions (https://e-lighthouse.com/) implementation is consuming the IS-IS network topology information exported by a commercial controller, using the Yang model proposed in this draft. It is able to simulate the network behavior under different changes, covering the what-if, failure analysis, dimensioning and other use cases mentioned in this draft.¶
The authors would like to thank Pierre Francois for the review and suggestions the document.¶
This work is partially supported by the European Commission under grant agreement No. 101092766 (ALLEGRO Project) and Horizon 2020 Secured autonomic traffic management for a Tera of SDN flows (Teraflow) project (grant agreement number 101015857).¶