]> Orange

mohamed.boucadair@orange.com

Juniper

rroberts@juniper.net

Nokia

samier.barguil_giraldo@nokia.com

Telefonica

oscar.gonzalezdedios@telefonica.com

OPS opsawg Slice Service L3VPN L2VPN Automation Network Automation Orchestration service delivery Service provisioning service segmentation service flexibility service simplification Network Service 3GPP Network Slicing This document defines a YANG data model, referred to as the "AC Glue" model, to augment the LxVPN Service Model (LxSM) and LxVPN Network Model (LxNM) with references to attachment circuits (ACs). The AC Glue model enables a provider to associate Layer 2/3 VPN (LxVPN) services with the underlying AC infrastructure, thereby facilitating consistent provisioning and management of new or existing ACs in conjunction with LxVPN services. Specifically, by introducing an integrated approach to AC and LxVPN management, this model supports Attachment Circuit as a Service (ACaaS) and provides a standardized mechanism for aligning AC/VPN requests with the network configurations required to deliver them.

Introduction To facilitate data transfer within the provider network, it is assumed that the appropriate setup is provisioned over the links that connect customer termination points and a provider network (usually via a Provider Edge (PE)), allowing data to be successfully exchanged over these links. The required setup is referred to in this document as an attachment circuit (AC), while the underlying link is referred to as "bearer". The document specifies a YANG module ("ietf-ac-glue", ) that updates existing service and network Virtual Private Network (VPN) modules with the required information to bind specific services to ACs that are created using the AC service model . Specifically, the following modules are augmented:

• The L2VPN Service Model (L2SM)
• The L3VPN Service Model (L3SM)
• The L2VPN Network Model (L2NM)
• The L3VPN Network Model (L3NM)

Likewise, the document augments the L2NM and L3NM with references to the ACs that are managed using the AC network model . This approach allows operators to separate AC provisioning from actual VPN service provisioning. Refer to for more discussion. The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in . Examples to illustrate the use of the "ietf-ac-glue" module are provided in .

Conventions and Definitions The meanings of the symbols in the YANG tree diagrams are defined in . This document uses terms defined in . LxSM refers to both the L2SM and the L3SM. LxNM refers to both the L2NM and the L3NM. The following terms are used in the module's prefixes:

ac:

Attachment circuit

ntw:

Network

ref:

Reference

svc:

Service

The names of data nodes are prefixed using the prefix associated with the corresponding imported YANG module as shown in : Modules and Their Associated Prefixes

Prefix	Module	Reference
ac-svc	ietf-ac-svc
ac-ntw	ietf-ac-ntw
l2nm	ietf-l2vpn-ntw
l2vpn-svc	ietf-l2vpn-svc
l3nm	ietf-l3vpn-ntw
l3vpn-svc	ietf-l3vpn-svc

Relationship to Other AC Data Models depicts the relationship between the various AC data models:

• "ietf-ac-common"
• "ietf-bearer-svc" ()
• "ietf-ac-svc" ()
• "ietf-ac-ntw"
• "ietf-ac-glue" ()

AC Data Models Y: X imports Y ]]>

The "ietf-ac-common" module is imported by the "ietf-bearer-svc", "ietf-ac-svc", and "ietf-ac-ntw" modules. Bearers managed using the "ietf-bearer-svc" module may be referenced by service ACs managed using the "ietf-ac-svc" module. Similarly, a bearer managed using the "ietf-bearer-svc" module may list the set of ACs that use that bearer. To facilitate correlation between an AC service request and the actual AC provisioned in the network, "ietf-ac-ntw" leverages the AC references exposed by the "ietf-ac-svc" module. Furthermore, to bind Layer 2 VPN (L2VPN) or Layer 3 VPN (L3VPN) services with ACs, the "ietf-ac-glue" module augments the LxSM and LxNM with AC service references exposed by the "ietf-ac-svc" module and AC network references exposed by the "ietf-ac-ntw" module.

Sample Uses of the Data Models

ACs Terminated by One or Multiple Customer Edges (CEs) depicts two target topology flavors that involve ACs. These topologies have the following characteristics:

• A Customer Edge (CE) can be either a physical device or a logical entity. Such logical entity is typically a software component (e.g., a virtual service function that is hosted within the provider's network or a third-party infrastructure). A CE is seen by the network as a peer Service Attachment Point (SAP) .
• CEs may be either dedicated to one single connectivity service or host multiple connectivity services (e.g., CEs with roles of service functions ).
• A network provider may bind a single AC to one or multiple peer SAPs (e.g., CE1 and CE2 are tagged as peer SAPs for the same AC). For example, and as discussed in , multiple CEs can be attached to a PE over the same AC. This scenario is typically implemented when the Layer 2 infrastructure between the CE and the network is a multipoint service.
• A single CE may terminate multiple ACs, which can be associated with the same bearer or distinct bearers (e.g., CE4).
• Customers may request protection schemes in which the ACs associated with their endpoints are terminated by the same PE (e.g., CE3), distinct PEs (e.g., CE4), etc. The network provider uses this request to decide where to terminate the AC in the service provider network and also whether to enable specific capabilities (e.g., Virtual Router Redundancy Protocol (VRRP)).

Examples of ACs

These ACs can be referenced when creating VPN services. Refer to the examples provided in to illustrate how VPN services can be bound to ACs.

Separate AC Provisioning from Actual VPN Service Provisioning The procedure to provision a service in a service provider network may depend on the practices adopted by a service provider. This includes the flow put in place for the provisioning of advanced network services and how they are bound to an AC. For example, a single AC may be used to host multiple connectivity services (e.g., L2VPN ("ietf-l2vpn-svc"), L3VPN ("ietf-l3vpn-svc"), Network Slice Service ("ietf-network-slice-service")). In order to avoid service interference and redundant information in various locations, a service provider may expose an interface to manage ACs network-wide using the modules in . Customers can request for an AC ("ietf-ac-svc") to be put in place and then refer to that AC when requesting VPN services that are bound to the AC ("ietf-ac-glue"). Also, internal references ("ietf-ac-ntw") used within a service provider network to implement ACs can be used by network controllers to glue the L2NM ("ietf-l2vpn-ntw") or the L3NM ("ietf-l3vpn-ntw") services with relevant ACs. shows the positioning of the AC models in the overall service delivery process.

An Example of AC Models Usage

Module Tree Structure specifies that a 'site-network-access' attachment is achieved through a 'bearer' with an 'ip-connection' on top. From that standpoint, a 'site-network-access' is mapped to an AC with both Layer 2 and Layer 3 properties per . specifies that a 'site-network-access' represents a logical Layer 2 connection to a site. A 'site-network-access' can thus be mapped to an AC with Layer 2 properties . Similarly, 'vpn-network-access' defined in both and is mapped to an AC per or . As such, ACs created using the "ietf-ac-svc" module can be referenced in other VPN-related modules (e.g., LxSM and LxNM). Also, ACs managed using the "ietf-ac-ntw" module can be referenced in VPN-related network modules (mainly, the LxNM). The required augmentations to that aim are shown in .

AC Glue Tree Structure /nw:networks/network/network-id augment /l2nm:l2vpn-ntw/l2nm:vpn-services/l2nm:vpn-service /l2nm:vpn-nodes/l2nm:vpn-node/l2nm:vpn-network-accesses /l2nm:vpn-network-access: +--rw ac-svc-ref? ac-svc:attachment-circuit-reference {ac-glue}? +--rw ac-ntw-ref {ac-glue}? +--rw ac-ref? leafref +--rw node-ref? leafref +--rw network-ref? -> /nw:networks/network/network-id augment /l3nm:l3vpn-ntw/l3nm:vpn-services/l3nm:vpn-service /l3nm:vpn-nodes/l3nm:vpn-node/l3nm:vpn-network-accesses: +--rw ac-svc-ref* ac-svc:attachment-circuit-reference +--rw ac-ntw-ref* [ac-ref] +--rw ac-ref leafref +--rw node-ref? leafref +--rw network-ref? -> /nw:networks/network/network-id augment /l3nm:l3vpn-ntw/l3nm:vpn-services/l3nm:vpn-service /l3nm:vpn-nodes/l3nm:vpn-node/l3nm:vpn-network-accesses /l3nm:vpn-network-access: +--rw ac-svc-ref? ac-svc:attachment-circuit-reference {ac-glue}? +--rw ac-ntw-ref {ac-glue}? +--rw ac-ref? leafref +--rw node-ref? leafref +--rw network-ref? -> /nw:networks/network/network-id ]]>

When an AC is referenced within a specific network access, that AC information takes precedence over any overlapping information that is also enclosed for this network access. The "ietf-ac-glue" module includes provisions to reference ACs within or outside a VPN network access to accommodate deployment contexts where an AC reference may be created before or after a VPN instance is created. illustrates how an AC reference can be included as part of a specific VPN network access, while shows how AC references can be indicated outside individual VPN network access entries.

The AC Glue ("ietf-ac-glue") YANG Module This modules augments the L2SM , the L3SM , the L2NM , and the L3NM . This module uses references defined in and . WG List: Editor: Mohamed Boucadair Author: Richard Roberts Author: Samier Barguil Author: Oscar Gonzalez de Dios "; description "This YANG module defines a YANG data model for augmenting the LxSM and the LxNM with AC references. Copyright (c) 2025 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC 9836; see the RFC itself for full legal notices."; revision 2025-09-29 { description "Initial revision."; reference "RFC 9836: A YANG Data Model for Augmenting VPN Service and Network Models with Attachment Circuits"; } feature ac-glue { description "The VPN implementation supports binding a specific VPN network access or site access to an AC."; } grouping single-ac-svc-ref { description "A grouping with a single reference to a service AC."; leaf ac-svc-ref { type ac-svc:attachment-circuit-reference; description "A reference to the AC as exposed at the service that was provisioned using the ACaaS module."; } } grouping single-ac-svc-ntw-ref { description "A grouping with single AC references."; leaf ac-svc-ref { type ac-svc:attachment-circuit-reference; description "A reference to the AC as exposed at the service that was provisioned using the ACaaS module."; } container ac-ntw-ref { description "A reference to the AC that was provisioned using the AC network module."; uses ac-ntw:attachment-circuit-reference; } } grouping ac-svc-ref { description "A set of service-specific AC-related data."; leaf-list ac-svc-ref { type ac-svc:attachment-circuit-reference; description "A reference to the AC as exposed at the service that was provisioned using the ACaaS module."; } } grouping ac-svc-ntw-ref { description "A set of AC-related data."; leaf-list ac-svc-ref { type ac-svc:attachment-circuit-reference; description "A reference to the AC as exposed at the service that was provisioned using the ACaaS module."; } list ac-ntw-ref { key "ac-ref"; description "A reference to the AC that was provisioned using the AC network module."; uses ac-ntw:attachment-circuit-reference; } } augment "/l2vpn-svc:l2vpn-svc" + "/l2vpn-svc:sites/l2vpn-svc:site" + "/l2vpn-svc:site-network-accesses" { description "Augments VPN site network accesses with AC provisioning details. Concretely, it binds a site to a set of ACs with Layer 2 properties that were created using the ACaaS module."; uses ac-svc-ref; } augment "/l2vpn-svc:l2vpn-svc" + "/l2vpn-svc:sites/l2vpn-svc:site" + "/l2vpn-svc:site-network-accesses" + "/l2vpn-svc:site-network-access" { if-feature "ac-glue"; description "Augments VPN site network access with AC provisioning details. Concretely, it glues a 'site-network-access' to an AC with Layer 2 properties that was created using the ACaaS module. The ACaaS information takes precedence over any overlapping information that is also provided for a site network access."; uses single-ac-svc-ref; } augment "/l3vpn-svc:l3vpn-svc" + "/l3vpn-svc:sites/l3vpn-svc:site" + "/l3vpn-svc:site-network-accesses" { description "Augments VPN site network accesses with AC provisioning details. Concretely, it binds a site to a set of ACs with both Layer 2 and Layer 3 properties that were created using the ACaaS module."; uses ac-svc-ref; } augment "/l3vpn-svc:l3vpn-svc" + "/l3vpn-svc:sites/l3vpn-svc:site" + "/l3vpn-svc:site-network-accesses" + "/l3vpn-svc:site-network-access" { if-feature "ac-glue"; description "Augments VPN site network access with AC provisioning details. Concretely, it glues a 'site-network-access' to an AC with both Layer 2 and Layer 3 properties that was created using the ACaaS module. The ACaaS information takes precedence over any overlapping information that is also provided for a site network access."; uses single-ac-svc-ref; } augment "/l2nm:l2vpn-ntw/l2nm:vpn-services/l2nm:vpn-service" + "/l2nm:vpn-nodes/l2nm:vpn-node" + "/l2nm:vpn-network-accesses" { description "Augments VPN network accesses with both service and network AC provisioning details. Concretely, it binds a site to (1) a set of ACs with Layer 2 properties that were created using the ACaaS module and (2) a set of ACs with Layer 2 properties that were provisioned using the AC network model."; uses ac-svc-ntw-ref; } augment "/l2nm:l2vpn-ntw/l2nm:vpn-services/l2nm:vpn-service" + "/l2nm:vpn-nodes/l2nm:vpn-node" + "/l2nm:vpn-network-accesses" + "/l2nm:vpn-network-access" { if-feature "ac-glue"; description "Augments VPN network access with service and network references to an AC. Concretely, it glues a VPN network access to (1) an AC with Layer 2 properties that was created using the ACaaS module and (2) an AC with Layer 2 properties that was created using the AC network module. The AC service and network information takes precedence over any overlapping information that is also provided for a VPN network access."; uses single-ac-svc-ntw-ref; } augment "/l3nm:l3vpn-ntw/l3nm:vpn-services/l3nm:vpn-service" + "/l3nm:vpn-nodes/l3nm:vpn-node" + "/l3nm:vpn-network-accesses" { description "Augments VPN network accesses with both service and network AC provisioning details. Concretely, it binds a site to (1) a set of ACs with both Layer 2 and Layer 3 properties that were created using the ACaaS module and (2) a set of ACs with both Layer 2 and Layer 3 properties that were provisioned using the AC network model."; uses ac-svc-ntw-ref; } augment "/l3nm:l3vpn-ntw/l3nm:vpn-services/l3nm:vpn-service" + "/l3nm:vpn-nodes/l3nm:vpn-node" + "/l3nm:vpn-network-accesses" + "/l3nm:vpn-network-access" { if-feature "ac-glue"; description "Augments VPN network access with service and network references to an AC. Concretely, it glues a VPN network access to (1) an AC with both Layer 2 and Layer 3 properties that was created using the ACaaS module and (2) an AC with both Layer 2 and Layer 3 properties that was created using the AC network module. The AC service and network information takes precedence over any overlapping information that is also provided for a VPN network access."; uses single-ac-svc-ntw-ref; } } ]]>

Security Considerations This section is modeled after the template described in . The "ietf-ac-common" YANG module defines a data model that is designed to be accessed via YANG-based management protocols, such as NETCONF and RESTCONF . These protocols have to use a secure transport layer (e.g., SSH , TLS , and QUIC ) and have to use mutual authentication. The Network Configuration Access Control Model (NACM) 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). All writable data nodes are likely to be reasonably sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) and delete operations to these data nodes without proper protection or authentication can have a negative effect on network operations. The following subtrees and data nodes have particular sensitivities/vulnerabilities:

'ac-svc-ref' and 'ac-ntw-ref':

An attacker who is able to access network nodes can undertake various attacks, such as deleting a running VPN service, interrupting all the traffic of a client. Specifically, an attacker may modify (including delete) the ACs that are bound to a running service, leading to malfunctioning of the service and therefore to Service Level Agreement (SLA) violations. Such activity can be detected by adequately monitoring and tracking network configuration changes.

Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:

'ac-svc-ref' and 'ac-ntw-ref':

These references do not expose privacy-related information per se; however, 'ac-svc-ref' may be used to track the set of VPN instances in which a given customer is involved. Note that, unlike 'ac-svc-ref', 'ac-ntw-ref' is unique within the scope of a node and may multiplex many peer CEs.

IANA Considerations IANA has registered the following URI in the "ns" subregistry within the "IETF XML Registry" :

URI:

urn:ietf:params:xml:ns:yang:ietf-ac-glue

Registrant Contact:

The IESG.

XML:

N/A; the requested URI is an XML namespace.

IANA has registered the following YANG module in the "YANG Module Names" registry within the "YANG Parameters" registry group:

Name:

ietf-ac-glue

Maintained by IANA?

N

Namespace:

urn:ietf:params:xml:ns:yang:ietf-ac-glue

Prefix:

ac-glue

Reference:

RFC 9836

References Normative References Orange Juniper Telefonica Nokia Huawei Technologies Orange Juniper Telefonica Nokia Huawei Technologies Informative References Orange Juniper Telefonica Nokia Huawei Technologies YumaWorks Orange Huawei

Examples

A Service AC Reference Within the VPN Network Access Let us consider the example depicted in , which is inspired from . Each PE is servicing two CEs. Let us also assume that the service references to identify ACs with these CEs are shown in .

VPWS Topology Example

As shown in , the service AC references can be explicitly indicated in the L2NM query for the realization of the Virtual Private Wire Service (VPWS) ().

Example of VPWS Creation with AC Service References

Network and Service AC References Let us consider the example depicted in with two customer termination points (CE1 and CE2). Let us also assume that the bearers to attach these CEs to the service provider network are already in place. References to identify these bearers are shown in .

Topology Example

The AC service model can be used by the provider to manage and expose the ACs over existing bearers as shown in .

ACs Created Using ACaaS

Let us now consider that the customer wants to request a Virtual Private LAN Service (VPLS) instance between the sites as shown in .

Example of VPLS

To that aim, existing ACs are referenced during the creation of the VPLS instance using the L2NM and the "ietf-ac-glue" module as shown in .

Example of a VPLS Request Using L2NM and AC Glue (Message Body)

Note that before implementing the VPLS instance creation request, the provider service orchestrator may first check if the VPLS service can be provided to the customer using the target delivery locations. The orchestrator uses the SAP model as exemplified in . This example assumes that the query concerns only PE1. A similar query can be issued for PE2.

Example of SAP Response (Message Body)

The response in indicates that the VPLS service can be delivered to CE1. The "ietf-ac-ntw" module can be also used to access AC-related details that are bound to the target SAP ().

Example of AC Network Response with SAP (Message Body)

The provisioned AC at PE1 can be retrieved using the AC network model as depicted in .

Example of AC Network Response (Message Body)

Acknowledgments Thanks to and for the review and comments. Thanks to for the YANG Doctors review, for the RTGDIR review, for the OPSDIR review, for the GENART review, and for the SECDIR review. Thanks to for the AD review. Thanks to for the IESG review.