| RFC 8969 | Service & Network Management Automation | January 2021 |
| Wu, et al. | Informational | [Page] |
Data models provide a programmatic approach to represent services and networks. Concretely, they can be used to derive configuration information for network and service components, and state information that will be monitored and tracked. Data models can be used during the service and network management life cycle (e.g., service instantiation, service provisioning, service optimization, service monitoring, service diagnosing, and service assurance). Data models are also instrumental in the automation of network management, and they can provide closed-loop control for adaptive and deterministic service creation, delivery, and maintenance.¶
This document describes a framework for service and network management automation that takes advantage of YANG modeling technologies. This framework is drawn from a network operator perspective irrespective of the origin of a data model; thus, it can accommodate YANG modules that are developed outside the IETF.¶
This document is not an Internet Standards Track specification; it is published for informational purposes.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8969.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
Service management systems usually comprise service activation/provision and service operation. Current service delivery procedures, from the processing of customer requirements and orders to service delivery and operation, typically assume the manipulation of data sequentially into multiple Operations Support System (OSS) or Business Support System (BSS) applications that may be managed by different departments within the service provider's organization (e.g., billing factory, design factory, network operation center). Many of these applications have been developed in house over the years and operate in a silo mode. As a result:¶
Software-Defined Networking (SDN) becomes crucial to address these challenges. SDN techniques are meant to automate the overall service delivery procedures and typically rely upon standard data models. These models are used not only to reflect service providers' savoir faire, but also to dynamically instantiate and enforce a set of service-inferred policies that best accommodate what has been defined and possibly negotiated with the customer. [RFC7149] provides a first tentative attempt to rationalize that service provider's view on the SDN space by identifying concrete technical domains that need to be considered and for which solutions can be provided. These include:¶
Models are key for each of the four technical items above. Service and network management automation is an important step to improve the agility of network operations. Models are also important to ease integrating multi-vendor solutions.¶
YANG module [RFC7950] developers have taken both top-down and bottom-up approaches to develop modules [RFC8199] and to establish a mapping between a network technology and customer requirements at the top or abstracting common constructs from various network technologies at the bottom. At the time of writing this document (2020), there are many YANG data models, including configuration and service models, that have been specified or are being specified by the IETF. They cover many of the networking protocols and techniques. However, how these models work together to configure a function, manage a set of devices involved in a service, or provide a service is something that is not currently documented either within the IETF or other Standards Development Organizations (SDOs).¶
Many of the YANG modules listed in this document are used to exchange data between NETCONF/RESTCONF clients and servers [RFC6241][RFC8040]. Nevertheless, YANG is a transport-independent data modeling language. It can thus be used independently of NETCONF/RESTCONF. For example, YANG can be used to define abstract data structures [RFC8791] that can be manipulated by other protocols (e.g., [DOTS-DDOS]).¶
This document describes an architectural framework for service and network management automation (Section 3) that takes advantage of YANG modeling technologies and investigates how YANG data models at different layers interact with each other (e.g., Service Mapping, model composition) in the context of service delivery and fulfillment (Section 4). Concretely, the following benefits can be provided:¶
This framework is drawn from a network operator perspective irrespective of the origin of a data model; it can also accommodate YANG modules that are developed outside the IETF. The document covers service models that are used by an operator to expose its services and capture service requirements from the customers (including other operators). Nevertheless, the document does not elaborate on the communication protocol(s) that makes use of these service models in order to request and deliver a service. Such considerations are out of scope.¶
The document identifies a list of use cases to exemplify the proposed approach (Section 5), but it does not claim nor aim to be exhaustive. Appendix A lists some examples to illustrate the layered YANG modules view.¶
The following terms are defined in [RFC8309] and [RFC8199] and are not redefined here:¶
In addition, the document makes use of the following terms:¶
Describes a network-level abstraction (or a subset of aspects of a network infrastructure), including devices and their subsystems, and relevant protocols operating at the link and network layers across multiple devices. This model corresponds to the network configuration model discussed in [RFC8309].¶
It can be used by a network operator to allocate resources (e.g., tunnel resource, topology resource) for the service or schedule resources to meet the service requirements defined in a service model.¶
Refers to the Network Element YANG data model described in [RFC8199] or the device configuration model discussed in [RFC8309].¶
Device models are also used to refer to model a function embedded in a device (e.g., Network Address Translation (NAT) [RFC8512], Access Control Lists (ACLs) [RFC8519]).¶
The following abbreviations are used in the document:¶
As described in Section 2 of [RFC8199], layering of modules allows for better reusability of lower-layer modules by higher-level modules while limiting duplication of features across layers.¶
Data models in the context of network management can be classified into service, network, and device models. Different service models may rely on the same set of network and/or device models.¶
Service models traditionally follow a top-down approach and are mostly customer-facing YANG modules providing a common model construct for higher-level network services (e.g., Layer 3 Virtual Private Network (L3VPN)). Such modules can be mapped to network technology-specific modules at lower layers (e.g., tunnel, routing, Quality of Service (QoS), security). For example, service models can be used to characterize the network service(s) to be ensured between service nodes (ingress/egress) such as:¶
Figure 1 depicts the example of a Voice over IP (VoIP) service that relies upon connectivity services offered by a network operator. In this example, the VoIP service is offered to the network operator's customers by Service Provider 1 (SP1). In order to provide global VoIP reachability, SP1 Service Site interconnects with other Service Providers service sites typically by interconnecting Session Border Elements (SBEs) and Data Border Elements (DBEs) [RFC5486][RFC6406]. For other VoIP destinations, sessions are forwarded over the Internet. These connectivity services can be captured in a YANG service model that reflects the service attributes that are shown in Figure 2. This example follows the IP Connectivity Provisioning Profile template defined in [RFC7297].¶
,--,--,--. ,--,--,--.
,-' SP1 `-. ,-' SP2 `-.
( Service Site ) ( Service Site )
`-. ,-' `-. ,-'
`--'--'--' `--'--'--'
x | o * * |
(2)x | o * * |
,x-,--o-*-. (1) ,--,*-,--.
,-' x o * * * * * * * * * `-.
( x o +----( Internet )
User---(x x x o o o o o o o o o o o o o o o o o o
`-. ,-' `-. ,-' (3)
`--'--'--' `--'--'--'
Network Operator
**** (1) Inter-SP connectivity
xxxx (2) Customer-to-SP connectivity
oooo (3) SP to any destination connectivity
In reference to Figure 2, "Full traffic performance guarantees class" refers to a service class where all traffic performance metrics included in the service model (OWD, loss, delay variation) are guaranteed, while "Delay traffic performance guarantees class" refers to a service class where only OWD is guaranteed.¶
Connectivity: Scope and Guarantees
(1) Inter-SP connectivity
- Pipe scope from the local to the remote SBE/DBE
- Full traffic performance guarantees class
(2) Customer-to-SP connectivity
- Hose/Funnel scope connecting the local SBE/DBE
to the customer access points
- Full traffic performance guarantees class
(3) SP to any destination connectivity
- Hose/Funnel scope from the local SBE/DBE to the
Internet gateway
- Delay traffic performance guarantees class
Flow Identification
* Destination IP address (SBE, DBE)
* DSCP marking
Traffic Isolation
* VPN
Routing & Forwarding
* Routing rule to exclude some ASes from the inter-domain
paths
Notifications (including feedback)
* Statistics on aggregate traffic to adjust capacity
* Failures
* Planned maintenance operations
* Triggered by thresholds
Network models are mainly network-resource-facing modules; they describe various aspects of a network infrastructure, including devices and their subsystems, and relevant protocols operating at the link and network layers across multiple devices (e.g., network topology and traffic-engineering tunnel modules).¶
Device (and function) models usually follow a bottom-up approach and are mostly technology-specific modules used to realize a service (e.g., BGP, ACL).¶
Each level maintains a view of the supported YANG modules provided by lower levels (see for example, Appendix A). Mechanisms such as the YANG library [RFC8525] can be used to expose which YANG modules are supported by nodes in lower levels.¶
Figure 3 illustrates the overall layering model. The reader may refer to Section 4 of [RFC8309] for an overview of "Orchestrator" and "Controller" elements. All these elements (i.e., Orchestrator(s), Controller(s), device(s)) are under the responsibility of the same operator.¶
+-----------------------------------------------------------------+ | Hierarchy Abstraction | | | | +-----------------------+ Service Model | | | Orchestrator | (Customer Oriented) | | |+---------------------+| Scope: "1:1" Pipe model | | || Service Modeling || | | |+---------------------+| | | | | Bidirectional | | |+---------------------+| +-+ Capacity, OWD +-+ | | ||Service Orchestration|| | +----------------+ | | | |+---------------------+| +-+ +-+ | | +-----------------------+ Ingress Egress | | | | | | +-----------------------+ Network Model | | | Controller | (Operator Oriented) | | |+---------------------+| +-+ +--+ +---+ +-+ | | || Network Modeling || | | | | | | | | | | |+---------------------+| | o----o--o----o---o---o | | | | | +-+ +--+ +---+ +-+ | | |+---------------------+| src dst | | ||Network Orchestration|| L3VPN over TE | | |+---------------------+| Instance Name/Access Interface | | +-----------------------+ Protocol Type/Capacity/RD/RT/... | | | | | | +-----------------------+ Device Model | | | Device | | | |+--------------------+ | | | || Device Modeling | | Interface add, BGP Peer, | | |+--------------------+ | Tunnel ID, QoS/TE, ... | | +-----------------------+ | +-----------------------------------------------------------------+
A composite service offered by a network operator may rely on services from other operators. In such a case, the network operator acts as a customer to request services from other networks. The operators providing these services will then follow the layering depicted in Figure 3. The mapping between a composite service and a third-party service is maintained at the orchestration level. From a data-plane perspective, appropriate traffic steering policies (e.g., Service Function Chaining [RFC7665]) are managed by the network controllers to guide how/when a third-party service is invoked for flows bound to a composite service.¶
The layering model depicted in Figure 3 does not make any assumption about the location of the various entities (e.g., Controller, Orchestrator) within the network. As such, the architecture does not preclude deployments where, for example, the Controller is embedded on a device that hosts other functions that are controlled via YANG modules.¶
In order to ease the mapping between layers and data reuse, this document focuses on service models that are modeled using YANG. Nevertheless, fully compliant with Section 3 of [RFC8309], Figure 3 does not preclude service models to be modeled using data modeling languages other than YANG.¶
Service models can be used by a network operator to expose its services to its customers. Exposing such models allows automation of the activation of service orders and thus the service delivery. One or more monolithic service models can be used in the context of a composite service activation request (e.g., delivery of a caching infrastructure over a VPN). Such models are used to feed a decision-making intelligence to adequately accommodate customer needs.¶
Also, such models may be used jointly with services that require dynamic invocation. An example is provided by the service modules defined by the DOTS WG to dynamically trigger requests to handle Distributed Denial-of-Service (DDoS) attacks [RFC8783]. The service filtering request modeled using [RFC8783] will be translated into device-specific filtering (e.g., ACLs defined in [RFC8519]) that fulfills the service request.¶
Network models can be derived from service models and used to provision, monitor, and instantiate the service. Also, they are used to provide life-cycle management of network resources. Doing so is meant to:¶
Note that it is out of the scope of this document to elaborate on the communication protocols that are used to implement the interface between the service ordering (customer) and service order handling (provider).¶
To operate a service, the settings of the parameters in the device models are derived from service models and/or network models and are used to:¶
In addition, the operational state including configuration that is in effect together with statistics should be exposed to upper layers to provide better network visibility and assess to what extent the derived low-level modules are consistent with the upper-level inputs.¶
Filters are enforced on the notifications that are communicated to Service layers. The type and frequency of notifications may be agreed upon in the service model.¶
Note that it is important to correlate telemetry data with configuration data to be used for closed loops at the different stages of service delivery, from resource allocation to service operation, in particular.¶
To support top-down service delivery, YANG modules at different levels or at the same level need to be integrated for proper service delivery (including proper network setup). For example, the service parameters captured in service models need to be decomposed into a set of configuration/notification parameters that may be specific to one or more technologies; these technology-specific parameters are grouped together to define technology-specific device-level models or network-level models.¶
In addition, these technology-specific device or network models can be further integrated with each other using the schema mount mechanism [RFC8528] to provision each involved network function/device or each involved network domain to support newly added modules or features. A collection of integrated device models can be loaded and validated during implementation.¶
High-level policies can be defined at service or network models (e.g., "Autonomous System Number (ASN) Exclude" in the example depicted in Figure 2). Device models will be tweaked accordingly to provide policy-based management. Policies can also be used for telemetry automation, e.g., policies that contain conditions to trigger the generation and pushing of new telemetry data.¶
The architectural considerations described in Section 3 lead to the life-cycle management architecture illustrated in Figure 4 and described in the following subsections.¶
+------------------+
............... | |
Service level | |
V |
E2E E2E E2E E2E
Service --> Service ---------> Service ------------> Service
Exposure Creation ^ Optimization ^ Diagnosis
/Modification | | |
^ | |Diff | |
E2E | | | E2E | |
Service ----+ | | Service | |
Decommission | +------ Assurance --+ |
| ^ |
Multi-layer | | |
Multi-domain | | |
Service Mapping| | |
............... |<-----------------+ | |
Network level | | +-------+ v
V | | Specific
Specific Specific | Service
Service --------> Service <--+ | Diagnosis
Creation ^ Optimization | | |
/Modification | | | |
| |Diff | | |
| | Specific --+ | |
Service | | Service | |
Decomposition | +----- Assurance ----+ |
| ^ |
............... | | Aggregation |
Device level | +------------+ |
V | |
Service Intent | v
Fulfillment Config ----> Config ----> Performance ----> Fault
Provision Validation Monitoring Diagnostic
Service life-cycle management includes end-to-end service life-cycle management at the service level and technology-specific network life-cycle management at the network level.¶
The end-to-end service life-cycle management is technology-independent service management and spans across multiple network domains and/or multiple layers while technology-specific service life-cycle management is technology domain-specific or layer-specific service life-cycle management.¶
A service in the context of this document (sometimes called "Network Service") is some form of connectivity between customer sites and the Internet or between customer sites across the operator's network and across the Internet.¶
Service exposure is used to capture services offered to customers (ordering and order handling). One example is that a customer can use an L3VPN Service Model (L3SM) to request L3VPN service by providing the abstract technical characterization of the intended service between customer sites.¶
Service model catalogs can be created to expose the various services and the information needed to invoke/order a given service.¶
A customer is usually unaware of the technology that the network operator has available to deliver the service, so the customer does not make requests specific to the underlying technology but is limited to making requests specific to the service that is to be delivered. This service request can be filled using a service model.¶
Upon receiving a service request, and assuming that appropriate authentication and authorization checks have been made with success, the service Orchestrator/management system should verify whether the service requirements in the service request can be met (i.e., whether there are sufficient resources that can be allocated with the requested guarantees).¶
If the request is accepted, the service Orchestrator/management system maps such a service request to its view. This view can be described as a technology-specific network model or a set of technology-specific device models, and this mapping may include a choice of which networks and technologies to use depending on which service features have been requested.¶
In addition, a customer may require a change in the underlying network infrastructure to adapt to new customers' needs and service requirements (e.g., service a new customer site, add a new access link, or provide disjoint paths). This service modification can be issued following the same service model used by the service request.¶
Withdrawing a service is discussed in Section 4.1.6.¶
The performance measurement telemetry (Section 4.2.3) can be used to provide service assurance at service and/or network levels. The performance measurement telemetry model can tie with service or network models to monitor network performance or Service Level Agreements.¶
Service optimization is a technique that gets the configuration of the network updated due to network changes, incident mitigation, or new service requirements. One example is once a tunnel or a VPN is set up, performance monitoring information or telemetry information per tunnel (or per VPN) can be collected and fed into the management system. If the network performance doesn't meet the service requirements, the management system can create new VPN policies capturing network service requirements and populate them into the network.¶
Both network performance information and policies can be modeled using YANG. With Policy-based management, self-configuration and self-optimization behavior can be specified and implemented.¶
The overall service optimization is managed at the service level, while the network level is responsible for the optimization of the specific network services it provides.¶
Operations, Administration, and Maintenance (OAM) are important networking functions for service diagnosis that allow network operators to:¶
When the network is down, service diagnosis should be in place to pinpoint the problem and provide recommendations (or instructions) for network recovery.¶
The service diagnosis information can be modeled as technology-independent Remote Procedure Call (RPC) operations for OAM protocols and technology-independent abstraction of key OAM constructs for OAM protocols [RFC8531][RFC8533]. These models can be used to provide consistent configuration, reporting, and presentation for the OAM mechanisms used to manage the network.¶
Refer to Section 4.2.4 for the device-specific side.¶
Service decommission allows a customer to stop the service by removing the service from active status, thus releasing the network resources that were allocated to the service. Customers can also use the service model to withdraw the subscription to a service.¶
Intended configuration at the device level is derived from network models at the network level or service models at the service level and represents the configuration that the system attempts to apply. Take L3SM as a service model example to deliver an L3VPN service; there is a need to map the L3VPN service view defined in the service model into a detailed intended configuration view defined by specific configuration models for network elements. The configuration information includes:¶
These specific configuration models can be used to configure Provider Edge (PE) and Customer Edge (CE) devices within a site, e.g., a BGP policy model can be used to establish VPN membership between sites and VPN service topology.¶
Note that in networks with legacy devices (that support proprietary modules or do not support YANG at all), an adaptation layer is likely to be required at the network level so that these devices can be involved in the delivery of the network services.¶
This interface is also used to handle service withdrawal (Section 4.1.6).¶
Configuration validation is used to validate intended configuration and ensure the configuration takes effect.¶
For example, if a customer creates an interface "eth-0/0/0" but the interface does not physically exist at this point, then configuration data appears in the <intended> status but does not appear in the <operational> datastore. More details about <intended> and <operational> datastores can be found in Section 5.1 of [RFC8342].¶
When a configuration is in effect in a device, the <operational> datastore holds the complete operational state of the device, including learned, system, default configuration, and system state. However, the configurations and state of a particular device do not have visibility on the whole network, nor can they show how packets are going to be forwarded through the entire network. Therefore, it becomes more difficult to operate the entire network without understanding the current status of the network.¶
The management system should subscribe to updates of a YANG datastore in all the network devices for performance monitoring purposes and build a full topological visibility of the network by aggregating (and filtering) these operational states from different sources.¶
When configuration is in effect in a device, some devices may be misconfigured (e.g., device links are not consistent in both sides of the network connection) or network resources might be misallocated. Therefore, services may be negatively affected without knowing the root cause in the network.¶
Technology-dependent nodes and RPC commands are defined in technology-specific YANG data models, which can use and extend the base model described in Section 4.1.5 to deal with these issues.¶
These RPC commands received in the technology-dependent node can be used to trigger technology-specific OAM message exchanges for fault verification and fault isolation. For example, Transparent Interconnection of Lots of Links (TRILL) Multi-destination Tree Verification (MTV) RPC command [TRILL-YANG-OAM] can be used to trigger Multi-Destination Tree Verification Messages (MTVMs) defined in [RFC7455] to verify TRILL distribution tree integrity.¶
Multi-layer/Multi-domain Service Mapping allows the mapping of an end-to-end abstract view of the service segmented at different layers and/or different network domains into domain-specific views.¶
One example is to map service parameters in the L3SM into configuration parameters such as Route Distinguisher (RD), Route Target (RT), and VRF in the L3VPN Network Model (L3NM).¶
Another example is to map service parameters in the L3SM into Traffic Engineered (TE) tunnel parameters (e.g., Tunnel ID) in TE model and Virtual Network (VN) parameters (e.g., Access Point (AP) list and VN members) in the YANG data model for VN operation [ACTN-VN-YANG].¶
Service Decomposition allows to decompose service models at the service level or network models at the network level into a set of device models at the device level. These device models may be tied to specific device types or classified into a collection of related YANG modules based on service types and features offered, and they may load at the implementation time before configuration is loaded and validated.¶
The following subsections provide some YANG data model integration examples.¶
In reference to Figure 5, the following steps are performed to deliver the L3VPN service within the network management automation architecture defined in Section 4:¶
The Customer requests to create two sites (as per Service Creation in Section 4.1.2) relying upon L3SM with each site having one network access connectivity, for example:¶
[UNI-TOPOLOGY] can be used for representing, managing, and controlling the User Network Interface (UNI) topology.¶
L3SM |
Service |
Model |
+------------------------+------------------------+
| +--------V--------+ |
| | Service Mapping | |
| +--------+--------+ |
| Orchestrator | |
+------------------------+------------------------+
L3NM | ^ UNI Topology Model
Network | |
Model | |
+------------------------+------------------------+
| +-----------V-----------+ |
| | Service Decomposition | |
| +--++---------------++--+ |
| || || |
| Controller || || |
+---------------++---------------++---------------+
|| ||
|| BGP, ||
|| QoS, ||
|| Interface, ||
+------------+| NI, |+------------+
| | IP | |
+--+--+ +--+--+ +--+--+ +--+--+
| CE1 +-------+ PE1 | | PE2 +-------+ CE2 |
+-----+ +-----+ +-----+ +-----+
L3NM inherits some of the data elements from the L3SM. Nevertheless, the L3NM as designed in [OPSAWG-L3SM-L3NM] does not expose some information to the above layer such as the capabilities of an underlying network (which can be used to drive service order handling) or notifications (to notify subscribers about specific events or degradations as per agreed SLAs). Some of this information can be provided using, e.g., [OPSAWG-YANG-VPN]. A target overall model is depicted in Figure 6.¶
L3SM | ^
Service | | Notifications
Model | |
+------------------------+------------------------+
| +--------V--------+ |
| | Service Mapping | |
| +--------+--------+ |
| Orchestrator | |
+------------------------+------------------------+
L3NM | ^ UNI Topology Model
Network| | L3NM Notifications
Model | | L3NM Capabilities
+------------------------+------------------------+
| +-----------V-----------+ |
| | Service Decomposition | |
| +--++---------------++--+ |
| || || |
| Controller || || |
+---------------++---------------++---------------+
|| ||
|| BGP, ||
|| QoS, ||
|| Interface, ||
+------------+| NI, |+------------+
| | IP | |
+--+--+ +--+--+ +--+--+ +--+--+
| CE1 +-------+ PE1 | | PE2 +-------+ CE2 |
+-----+ +-----+ +-----+ +-----+
Note that a similar analysis can be performed for Layer 2 VPNs (L2VPNs). An L2VPN Service Model (L2SM) is defined in [RFC8466], while the YANG L2VPN Network Model (L2NM) is specified in [OPSAWG-L2NM].¶
In reference to Figure 7, the following steps are performed to deliver the VN service within the network management automation architecture defined in Section 4:¶
|
VN |
Service |
Model |
+----------------------|--------------------------+
| Orchestrator | |
| +--------V--------+ |
| | Service Mapping | |
| +-----------------+ |
+----------------------+--------------------^-----+
TE | Telemetry |
Tunnel | Model |
Model | |
+----------------------V--------------------+-----+
| Controller |
| |
+-------------------------------------------------+
+-----+ +-----+ +-----+ +-----+
| CE1 +------+ PE1 | | PE2 +------+ CE2 |
+-----+ +-----+ +-----+ +-----+
In reference to Figure 8, the following steps are performed to monitor state changes of managed resources in a network device and provide device self management within the network management automation architecture defined in Section 4:¶
+----------------+
| <----+
| Controller | |
+-------+--------+ |
| |
| |
ECA | | ECA
Model | | Notification
| |
| |
+------------V-------------+-----+
|Device | |
| +-------+ +---------+ +--+---+ |
| | Event +-> Event +->Event | |
| | Source| |Condition| |Action| |
| +-------+ +---------+ +------+ |
+--------------------------------+
Many of the YANG modules cited in this document define 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 NETCONF access control model [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.¶
Security considerations specific to each of the technologies and protocols listed in the document are discussed in the specification documents of each of these protocols.¶
In order to prevent leaking sensitive information and the "confused deputy" problem [Hardy] in general, special care should be considered when translating between the various layers in Section 4 or when aggregating data retrieved from various sources. Authorization and authentication checks should be performed to ensure that data is available to an authorized entity. The network operator must enforce means to protect privacy-related information included in customer-facing models.¶
To detect misalignment between layers that might be induced by misbehaving nodes, upper layers should continuously monitor the perceived service (Section 4.1.4) and should proceed with checks to assess that the provided service complies with the expected service and that the data reported by an underlying layer is matching the perceived service by the above layer. Such checks are the responsibility of the service diagnosis (Section 4.1.5).¶
When a YANG module includes security-related parameters, it is recommended to include the relevant information as part of the service assurance to track the correct functioning of the security mechanisms.¶
Additional considerations are discussed in the following subsections.¶
A provider may rely on services offered by other providers to build composite services. Appropriate mechanisms should be enabled by the provider to monitor and detect a service disruption from these providers. The characterization of a service disruption (including mean time between failures and mean time to repair), the escalation procedure, and penalties are usually documented in contractual agreements (e.g., as described in Section 2.1 of [RFC4176]). Misbehaving peer providers will thus be identified and appropriate countermeasures will be applied.¶
The communication protocols that make use of a service model between a customer and an operator are out of scope. Relevant security considerations should be discussed in the specification documents of these protocols.¶
Security considerations specific to the network level are listed below:¶
Network operators should monitor and audit their networks to detect misbehaving nodes and abnormal behaviors. For example, OAM, as discussed in Section 4.1.5, can be used for that purpose.¶
Access to some data requires specific access privilege levels. Devices must check that a required access privilege is provided before granting access to specific data or performing specific actions.¶
This document has no IANA actions.¶
This appendix lists a set of YANG data models that can be used for the delivery of connectivity services. These models can be classified as service, network, or device models.¶
It is not the intent of this appendix to provide an inventory of tools and mechanisms used in specific network and service management domains; such inventory can be found in documents such as [RFC7276].¶
The reader may refer to the YANG Catalog (<https://www.yangcatalog.org>) or the public Github YANG repository (<https://github.com/YangModels/yang>) to query existing YANG models. The YANG Catalog includes some metadata to indicate the module type ('module-classification') [NETMOD-MODEL]. Note that the mechanism defined in [RFC8819] allows to associate tags with YANG modules in order to help classifying the modules.¶
As described in [RFC8309], the service is "some form of connectivity between customer sites and the Internet or between customer sites across the network operator's network and across the Internet". More concretely, an IP connectivity service can be defined as the IP transfer capability characterized by a (Source Nets, Destination Nets, Guarantees, Scope) tuple where "Source Nets" is a group of unicast IP addresses, "Destination Nets" is a group of IP unicast and/or multicast addresses, and "Guarantees" reflects the guarantees (expressed, for example, in terms of QoS, performance, and availability) to properly forward traffic to the said "Destination" [RFC7297]. The "Scope" denotes the network perimeter (e.g., between Provider Edge (PE) routers or Customer Nodes) where the said guarantees need to be provided.¶
For example:¶
L2SM and L3SM are customer service models as per [RFC8309].¶
Modularity and extensibility were among the leading design principles of the YANG data modeling language. As a result, the same YANG module can be combined with various sets of other modules and thus form a data model that is tailored to meet the requirements of a specific use case. [RFC8528] defines a mechanism, denoted "schema mount", that allows for mounting one data model consisting of any number of YANG modules at a specified location of another (parent) schema.¶
L2NM [OPSAWG-L2NM] and L3NM [OPSAWG-L3SM-L3NM] are examples of YANG network models.¶
Figure 9 depicts a set of additional network models such as topology and tunnel models:¶
+-------------------------------+-------------------------------+ | Topology YANG modules | Tunnel YANG modules | +-------------------------------+-------------------------------+ | +------------------+ | | | |Network Topologies| | +------+ +-----------+ | | | Model | | |Other | | TE Tunnel | | | +--------+---------+ | |Tunnel| +----+------+ | | | +---------+ | +------+ | | | +---+Service | | +----------+---------+ | | | |Topology | | | | | | | | +---------+ | | | | | | | +---------+ |+----+---+ +----+---+ +---+---+| | +---+Layer 3 | ||MPLS-TE | |RSVP-TE | | SR-TE || | | |Topology | || Tunnel | | Tunnel | |Tunnel || | | +---------+ |+--------+ +--------+ +-------+| | | +---------+ | | | +---+TE | | | | | |Topology | | | | | +---------+ | | | | +---------+ | | | +---+Layer 3 | | | | |Topology | | | | +---------+ | | +-------------------------------+-------------------------------+
Examples of topology YANG modules are listed below:¶
[RFC8795] defines a YANG data model for representing and manipulating TE topologies.¶
This module is extended from the network topology model defined in [RFC8345] and includes content related to TE topologies. This model contains technology-agnostic TE topology building blocks that can be augmented and used by other technology-specific TE topology models.¶
[RFC8346] defines a YANG data model for representing and manipulating Layer 3 topologies. This model is extended from the network topology model defined in [RFC8345] and includes content related to Layer 3 topology specifics.¶
[RFC8944] defines a YANG data model for representing and manipulating Layer 2 topologies. This model is extended from the network topology model defined in [RFC8345] and includes content related to Layer 2 topology specifics.¶
Examples of tunnel YANG modules are provided below:¶
Other sample network models are listed hereafter:¶
[RFC8532] defines a base YANG module for the management of OAM protocols that use Connectionless Communications. [RFC8533] defines a retrieval method YANG module for connectionless OAM protocols. [RFC8531] defines a base YANG module for connection-oriented OAM protocols. These three models are intended to provide consistent reporting, configuration, and representation for connectionless OAM and connection-oriented OAM separately.¶
Alarm monitoring is a fundamental part of monitoring the network. Raw alarms from devices do not always tell the status of the network services or necessarily point to the root cause. [RFC8632] defines a YANG module for alarm management.¶
Network Element models (listed in Figure 10) are used to describe how a service can be implemented by activating and tweaking a set of functions (enabled in one or multiple devices, or hosted in cloud infrastructures) that are involved in the service delivery. For example, the L3VPN service will involve many PEs and require manipulating the following modules:¶
Figure 10 uses IETF-defined data models as an example.¶
+------------------------+
+-+ Device Model |
| +------------------------+
| +------------------------+
+---------------+ | | Logical Network |
| | +-+ Element Model |
| Architecture | | +------------------------+
| | | +------------------------+
+-------+-------+ +-+ Network Instance Model |
| | +------------------------+
| | +------------------------+
| +-+ Routing Type Model |
| +------------------------+
+-------+----------+----+------+------------+-----------+------+
| | | | | | |
+-+-+ +---+---+ +----+----+ +--+--+ +----+----+ +--+--+ |
|ACL| |Routing| |Transport| | OAM | |Multicast| | PM | Others
+---+ +-+-----+ +----+----+ +--+--+ +-----+---+ +--+--+
| +-------+ | +------+ | +--------+ | +-----+ | +-----+
+-+Core | +-+ MPLS | +-+ BFD | +-+IGMP | +-+TWAMP|
| |Routing| | | Base | | +--------+ | |/MLD | | +-----+
| +-------+ | +------+ | +--------+ | +-----+ | +-----+
| +-------+ | +------+ +-+LSP Ping| | +-----+ +-+OWAMP|
+-+ BGP | +-+ MPLS | | +--------+ +-+ PIM | | +-----+
| +-------+ | | LDP | | +--------+ | +-----+ | +-----+
| +-------+ | +------+ +-+MPLS-TP | | +-----+ +-+LMAP |
+-+ ISIS | | +------+ +--------+ +-+ MVPN| +-----+
| +-------+ +-+ MPLS | +-----+
| +-------+ |Static|
+-+ OSPF | +------+
| +-------+
| +-------+
+-+ RIP |
| +-------+
| +-------+
+-+ VRRP |
| +-------+
| +-------+
+-+SR/SRv6|
| +-------+
| +-------+
+-+ISIS-SR|
| +-------+
| +-------+
+-+OSPF-SR|
+-------+
The following list enumerates some YANG modules that can be used for device management:¶
The following provides some YANG modules that can be used for interface management:¶
The following provides an overview of some device models that can be used within a network. This list is not comprehensive.¶
[SPRING-SR-YANG] defines a YANG module for segment routing configuration and operation.¶
[PIM-YANG] defines a YANG module that can be used to configure and manage Protocol Independent Multicast (PIM) devices.¶
[RFC8652] defines a YANG module that can be used to configure and manage Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) devices.¶
[SNOOPING-YANG] defines a YANG module that can be used to configure and manage Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) snooping devices.¶
[MVPN-YANG] defines a YANG data model to configure and manage Multicast in MPLS/BGP IP VPNs (MVPNs).¶
[TWAMP-DATA-MODEL] defines a YANG data model for client and server implementations of the Two-Way Active Measurement Protocol (TWAMP).¶
[STAMP-YANG] defines the data model for implementations of Session-Sender and Session-Reflector for Simple Two-way Active Measurement Protocol (STAMP) mode using YANG.¶
[RFC8194] defines a YANG data model for Large-Scale Measurement Platforms (LMAPs).¶
For the sake of network automation and the need for programming the Network Address Translation (NAT) function in particular, a YANG data model for configuring and managing the NAT is essential.¶
[RFC8512] defines a YANG module for the NAT function covering a variety of NAT flavors such as Network Address Translation from IPv4 to IPv4 (NAT44), Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers (NAT64), customer-side translator (CLAT), Stateless IP/ICMP Translation (SIIT), Explicit Address Mappings (EAMs) for SIIT, IPv6-to-IPv6 Network Prefix Translation (NPTv6), and Destination NAT.¶
[RFC8513] specifies a Dual-Stack Lite (DS-Lite) YANG module.¶
Thanks to Joe Clark, Greg Mirsky, Shunsuke Homma, Brian Carpenter, Adrian Farrel, Christian Huitema, Tommy Pauly, Ines Robles, and Olivier Augizeau for the review.¶
Many thanks to Robert Wilton for the detailed AD review.¶
Thanks to Éric Vyncke, Roman Danyliw, Erik Kline, and Benjamin Kaduk for the IESG review.¶