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A Common YANG Data Model for Layer 2 and Layer 3 VPNs
RFC 9181

Document Type RFC - Proposed Standard (February 2022)
Authors Samier Barguil , Oscar Gonzalez de Dios , Mohamed Boucadair , Qin Wu
Last updated 2022-02-15
Replaces draft-bgbw-opsawg-vpn-common
Stream Internet Engineering Task Force (IETF)
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Yang Validation 0 errors, 0 warnings
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Additional resources Yang catalog entry for ietf-vpn-common@2020-10-26.yang
Yang impact analysis for draft-ietf-opsawg-vpn-common
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Stream WG state Submitted to IESG for Publication
Document shepherd Adrian Farrel
Shepherd write-up Show Last changed 2021-09-23
IESG IESG state RFC 9181 (Proposed Standard)
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Consensus boilerplate Yes
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Responsible AD Robert Wilton
Send notices to adrian@olddog.co.uk
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
IANA expert review state Expert Reviews OK
RFC 9181


Internet Engineering Task Force (IETF)                        S. Barguil
Request for Comments: 9181                      O. Gonzalez de Dios, Ed.
Category: Standards Track                                     Telefonica
ISSN: 2070-1721                                        M. Boucadair, Ed.
                                                                  Orange
                                                                   Q. Wu
                                                                  Huawei
                                                           February 2022

         A Common YANG Data Model for Layer 2 and Layer 3 VPNs

Abstract

   This document defines a common YANG module that is meant to be reused
   by various VPN-related modules such as Layer 3 VPN and Layer 2 VPN
   network models.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc9181.

Copyright Notice

   Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Description of the VPN Common YANG Module
   4.  Layer 2/3 VPN Common Module
   5.  Security Considerations
   6.  IANA Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Example of Common Data Nodes in Early L2NM/L3NM
           Designs
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   The IETF has specified YANG modules for VPN services, e.g., the Layer
   3 VPN Service Model (L3SM) [RFC8299] or the Layer 2 VPN Service Model
   (L2SM) [RFC8466].  Other relevant YANG data models are the Layer 3
   VPN Network Model (L3NM) [RFC9182] and the Layer 2 VPN Network Model
   (L2NM) [L2NM-YANG].  There are common data nodes and structures that
   are present in all of these models or at least a subset of them.

   This document defines a common YANG module that is meant to be reused
   by various VPN-related modules such as the L3NM [RFC9182] and the
   L2NM [L2NM-YANG]: "ietf-vpn-common" (Section 4).

   The "ietf-vpn-common" module includes a set of identities, types, and
   groupings that are meant to be reused by other VPN-related YANG
   modules independently of their layer (e.g., Layer 2, Layer 3) and the
   type of the module (e.g., network model, service model), including
   possible future revisions of existing models (e.g., the L3SM
   [RFC8299] or the L2SM [RFC8466]).

2.  Terminology

   The terminology for describing YANG modules is defined in [RFC7950].

   The meanings of the symbols in tree diagrams are defined in
   [RFC8340].

   The reader may refer to [RFC4026] and [RFC4176] for VPN-related
   terms.

   This document inherits many terms from [RFC8299] and [RFC8466] (e.g.,
   Enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency
   Communications (URLLC), Massive Machine Type Communications (mMTC)).

3.  Description of the VPN Common YANG Module

   The "ietf-vpn-common" module defines a set of common VPN-related
   features, including the following:

   Encapsulation features, such as the following:
      *  dot1Q [IEEE802.1Q],

      *  QinQ [IEEE802.1ad],

      *  link aggregation [IEEE802.1AX], and

      *  Virtual eXtensible Local Area Networks (VXLANs) [RFC7348].

   Multicast [RFC6513].

   Routing features, such as the following:
      *  BGP [RFC4271],

      *  OSPF [RFC4577] [RFC6565],

      *  IS-IS [ISO10589],

      *  RIP [RFC2080] [RFC2453],

      *  Bidirectional Forwarding Detection (BFD) [RFC5880] [RFC7880],
         and

      *  Virtual Router Redundancy Protocol (VRRP) [RFC5798].

   Also, the module defines a set of identities, including the
   following:

   'service-type':  Used to identify the VPN service type.  Examples of
      supported service types are as follows:

      *  L3VPN,

      *  Virtual Private LAN Service (VPLS) using BGP [RFC4761],

      *  VPLS using the Label Distribution Protocol (LDP) [RFC4762],

      *  Virtual Private Wire Service (VPWS) [RFC8214],

      *  BGP MPLS-Based Ethernet VPN [RFC7432],

      *  Ethernet VPN (EVPN) [RFC8365], and

      *  Provider Backbone Bridging Combined with Ethernet VPN
         (PBB-EVPN) [RFC7623].

   'vpn-signaling-type':  Used to identify the signaling mode used for a
      given service type.  Examples of supported VPN signaling types are
      as follows:

      *  L2VPNs using BGP [RFC6624],

      *  LDP [RFC5036], and

      *  Layer Two Tunneling Protocol (L2TP) [RFC3931].

   The module covers both IPv4 [RFC0791] and IPv6 [RFC8200] identities.
   It also includes multicast-related identities such as Internet Group
   Management Protocol version 1 (IGMPv1) [RFC1112], IGMPv2 [RFC2236],
   IGMPv3 [RFC3376], Multicast Listener Discovery version 1 (MLDv1)
   [RFC2710], MLDv2 [RFC3810], and Protocol Independent Multicast (PIM)
   [RFC7761].

   The reader should refer to Section 4 for the full list of supported
   identities (identities related to address families, VPN topologies,
   network access types, operational and administrative status, site or
   node role, VPN service constraints, routing protocols, route import
   and export policies, bandwidth, Quality of Service (QoS), etc.).

   The "ietf-vpn-common" module also contains a set of reusable VPN-
   related groupings.  Figure 1 provides the tree diagram that depicts
   the common groupings for the "ietf-vpn-common" module.

   module: ietf-vpn-common
     grouping vpn-description:
       +-- vpn-id?            vpn-id
       +-- vpn-name?          string
       +-- vpn-description?   string
       +-- customer-name?     string
     grouping vpn-profile-cfg:
       +-- valid-provider-identifiers
          +-- external-connectivity-identifier* [id]
          |       {external-connectivity}?
          |  +-- id   string
          +-- encryption-profile-identifier* [id]
          |  +-- id   string
          +-- qos-profile-identifier* [id]
          |  +-- id   string
          +-- bfd-profile-identifier* [id]
          |  +-- id   string
          +-- forwarding-profile-identifier* [id]
          |  +-- id   string
          +-- routing-profile-identifier* [id]
             +-- id   string
     grouping oper-status-timestamp:
       +--ro status?         identityref
       +--ro last-change?   yang:date-and-time
     grouping service-status:
       +-- status
          +-- admin-status
          |  +-- status?         identityref
          |  +-- last-change?    yang:date-and-time
          +--ro oper-status
             +--ro status?         identityref
             +--ro last-change?    yang:date-and-time
     grouping underlay-transport:
       +-- (type)?
          +--:(abstract)
          |  +-- transport-instance-id?   string
          |  +-- instance-type?           identityref
          +--:(protocol)
             +-- protocol*                identityref
     grouping vpn-route-targets:
       +-- vpn-target* [id]
       |  +-- id                  uint8
       |  +-- route-targets* [route-target]
       |  |  +-- route-target      rt-types:route-target
       |  +-- route-target-type    rt-types:route-target-type
       +-- vpn-policies
          +-- import-policy?   string
          +-- export-policy?   string
     grouping route-distinguisher:
       ...
     grouping vpn-components-group:
       +-- groups
          +-- group* [group-id]
             +-- group-id    string
     grouping placement-constraints:
       +-- constraint* [constraint-type]
          +-- constraint-type?   identityref
          +-- target
             +-- (target-flavor)?
                +--:(id)
                |  +-- group* [group-id]
                |     +-- group-id    string
                +--:(all-accesses)
                |  +-- all-other-accesses?   empty
                +--:(all-groups)
                   +-- all-other-groups?     empty
     grouping ports:
       ...
     grouping qos-classification-policy:
       ...

                         Figure 1: VPN Common Tree

   The descriptions of the common groupings are provided below:

   'vpn-description':
      A YANG grouping that provides common administrative VPN
      information such as an identifier, a name, a textual description,
      and a customer name.

   'vpn-profile-cfg':
      A YANG grouping that defines a set of valid profiles (encryption,
      routing, forwarding, etc.) that can be bound to a Layer 2/3 VPN.
      This document does not make any assumptions about the structure of
      such profiles but allows "gluing" a VPN service with other
      parameters that can be required locally to provide value-added
      features to requesting customers.

      For example, a service provider may provide external connectivity
      to a VPN customer (e.g., to a private or public cloud, Internet).
      Such a service may involve tweaking both filtering and NAT rules
      (e.g., binding a Virtual Routing and Forwarding (VRF) interface
      with a NAT instance as discussed in Section 2.10 of [RFC8512]).
      These value-added features may be bound to all, or a subset of,
      network accesses.  Some of these value-added features may be
      implemented in nodes other than Provider Edges (PEs) (e.g., a P
      node or even a dedicated node that hosts the NAT function).

      Elaborating on the structure of these profiles is beyond the scope
      of this document.

   'oper-status-timestamp':
      A YANG grouping that defines the operational status updates of a
      VPN service or component.

   'service-status':
      A YANG grouping that defines the administrative and operational
      status of a component.  The grouping can be applied to the whole
      service or an endpoint.

   'underlay-transport':
      A YANG grouping that defines the type of the underlay transport
      for a VPN service or how that underlay is set.

      The underlay transport can be expressed as an abstract transport
      instance (e.g., an identifier of a VPN+ instance
      [Enhanced-VPN-Framework], a virtual network identifier
      [ACTN-VN-YANG] [RFC8453], or a network slice name
      [Network-Slices-Framework]) or as an ordered list of the actual
      protocols to be enabled in the network.

      The module supports a rich set of protocol identifiers that can be
      used, for example, to refer to an underlay transport.  Examples of
      supported protocols are as follows:

      *  IP in IP [RFC2003] [RFC2473],

      *  Generic Routing Encapsulation (GRE) [RFC1701] [RFC1702]
         [RFC7676],

      *  MPLS in UDP [RFC7510],

      *  Generic Network Virtualization Encapsulation (Geneve)
         [RFC8926],

      *  Segment Routing (SR) [RFC8660] [RFC8663] [RFC8754],

      *  Resource ReSerVation Protocol (RSVP) with traffic engineering
         extensions [RFC3209], and

      *  BGP with labeled prefixes [RFC8277].

   'vpn-route-targets':
      A YANG grouping that defines Route Target (RT) import/export rules
      used in a BGP-enabled VPN.  This grouping can be used for both
      L3VPNs [RFC4364] and L2VPNs [RFC4664].  Note that this is modeled
      as a list to ease the reuse of this grouping in modules where an
      RT identifier is needed (e.g., associating an operator with RTs).

   'route-distinguisher':
      A YANG grouping that defines Route Distinguishers (RDs).

      As depicted in Figure 2, the module supports the following RD
      assignment modes: direct assignment, full automatic assignment,
      automatic assignment from a given pool, and no assignment.

      Also, the module accommodates deployments where only the Assigned
      Number subfield of RDs (Section 4.2 of [RFC4364]) is assigned from
      a pool while the Administrator subfield is set to, for example,
      the Router ID that is assigned to a VPN node.  The module supports
      three modes for managing the Assigned Number subfield: explicit
      assignment, automatic assignment from a given pool, and full
      automatic assignment.

        grouping route-distinguisher:
          +-- (rd-choice)?
             +--:(directly-assigned)
             |  +-- rd?               rt-types:route-distinguisher
             +--:(directly-assigned-suffix)
             |  +-- rd-suffix?        uint16
             +--:(auto-assigned)
             |  +-- rd-auto
             |     +-- (auto-mode)?
             |     |  +--:(from-pool)
             |     |  |  +-- rd-pool-name?   string
             |     |  +--:(full-auto)
             |     |     +-- auto?           empty
             |     +--ro auto-assigned-rd?
             |     |       rt-types:route-distinguisher
             +--:(auto-assigned-suffix)
             |  +-- rd-auto-suffix
             |     +-- (auto-mode)?
             |     |  +--:(from-pool)
             |     |  |  +-- rd-pool-name?        string
             |     |  +--:(full-auto)
             |     |     +-- auto?                empty
             |     +--ro auto-assigned-rd-suffix?   uint16
             +--:(no-rd)
                +-- no-rd?            empty

                Figure 2: Route Distinguisher Grouping Subtree

   'vpn-components-group':
      A YANG grouping that is used to group VPN nodes, VPN network
      accesses, or sites.  For example, diversity or redundancy
      constraints can be applied on a per-group basis.

   'placement-constraints':
      A YANG grouping that is used to define the placement constraints
      of a VPN node, VPN network access, or site.

   'ports':
      A YANG grouping that defines ranges of source and destination port
      numbers and operators.  The subtree of this grouping is depicted
      in Figure 3.

        grouping ports:
          +-- (source-port)?
          |  +--:(source-port-range-or-operator)
          |     +-- source-port-range-or-operator
          |        +-- (port-range-or-operator)?
          |           +--:(range)
          |           |  +-- lower-port    inet:port-number
          |           |  +-- upper-port    inet:port-number
          |           +--:(operator)
          |              +-- operator?     operator
          |              +-- port          inet:port-number
          +-- (destination-port)?
             +--:(destination-port-range-or-operator)
                +-- destination-port-range-or-operator
                   +-- (port-range-or-operator)?
                      +--:(range)
                      |  +-- lower-port    inet:port-number
                      |  +-- upper-port    inet:port-number
                      +--:(operator)
                         +-- operator?     operator
                         +-- port          inet:port-number

                   Figure 3: Port Numbers Grouping Subtree

   'qos-classification-policy':
      A YANG grouping that defines a set of QoS classification policies
      based on various Layer 3/4 and application match criteria.  The
      subtree of this grouping is depicted in Figure 4.

      The QoS match criteria reuse groupings that are defined in the
      packet fields module "ietf-packet-fields" (Section 4.2 of
      [RFC8519]).

      Any Layer 4 protocol can be indicated in the 'protocol' data node
      under 'l3', but only TCP- and UDP-specific match criteria are
      elaborated on in this version, as these protocols are widely used
      in the context of VPN services.  Future revisions can be
      considered to add other Layer-4-specific parameters (e.g., the
      Stream Control Transmission Protocol [RFC4960]), if needed.

      Some transport protocols use existing protocols (e.g., TCP or UDP)
      as the substrate.  The match criteria for such protocols may rely
      upon the 'protocol' under 'l3', TCP/UDP match criteria as shown in
      Figure 4, part of the TCP/UDP payload, or a combination thereof.
      This version of the module does not support such advanced match
      criteria.  Future revisions of the module may consider adding
      match criteria based on the transport protocol payload (e.g., by
      means of a bitmask match).

        grouping qos-classification-policy:
          +-- rule* [id]
             +-- id                         string
             +-- (match-type)?
             |  +--:(match-flow)
             |  |  +-- (l3)?
             |  |  |  +--:(ipv4)
             |  |  |  |  +-- ipv4
             |  |  |  |     +-- dscp?                          inet:dscp
             |  |  |  |     +-- ecn?                           uint8
             |  |  |  |     +-- length?                        uint16
             |  |  |  |     +-- ttl?                           uint8
             |  |  |  |     +-- protocol?                      uint8
             |  |  |  |     +-- ihl?                           uint8
             |  |  |  |     +-- flags?                         bits
             |  |  |  |     +-- offset?                        uint16
             |  |  |  |     +-- identification?                uint16
             |  |  |  |     +-- (destination-network)?
             |  |  |  |     |  +--:(destination-ipv4-network)
             |  |  |  |     |     +-- destination-ipv4-network?
             |  |  |  |     |             inet:ipv4-prefix
             |  |  |  |     +-- (source-network)?
             |  |  |  |        +--:(source-ipv4-network)
             |  |  |  |           +-- source-ipv4-network?
             |  |  |  |                   inet:ipv4-prefix
             |  |  |  +--:(ipv6)
             |  |  |     +-- ipv6
             |  |  |        +-- dscp?                          inet:dscp
             |  |  |        +-- ecn?                           uint8
             |  |  |        +-- length?                        uint16
             |  |  |        +-- ttl?                           uint8
             |  |  |        +-- protocol?                      uint8
             |  |  |        +-- (destination-network)?
             |  |  |        |  +--:(destination-ipv6-network)
             |  |  |        |     +-- destination-ipv6-network?
             |  |  |        |             inet:ipv6-prefix
             |  |  |        +-- (source-network)?
             |  |  |        |  +--:(source-ipv6-network)
             |  |  |        |     +-- source-ipv6-network?
             |  |  |        |             inet:ipv6-prefix
             |  |  |        +-- flow-label?
             |  |  |                inet:ipv6-flow-label
             |  |  +-- (l4)?
             |  |     +--:(tcp)
             |  |     |  +-- tcp
             |  |     |     +-- sequence-number?               uint32
             |  |     |     +-- acknowledgement-number?        uint32
             |  |     |     +-- data-offset?                   uint8
             |  |     |     +-- reserved?                      uint8
             |  |     |     +-- flags?                         bits
             |  |     |     +-- window-size?                   uint16
             |  |     |     +-- urgent-pointer?                uint16
             |  |     |     +-- options?                       binary
             |  |     |     +-- (source-port)?
             |  |     |     |  +--:(source-port-range-or-operator)
             |  |     |     |     +-- source-port-range-or-operator
             |  |     |     |        +-- (port-range-or-operator)?
             |  |     |     |           +--:(range)
             |  |     |     |           |  +-- lower-port
             |  |     |     |           |  |       inet:port-number
             |  |     |     |           |  +-- upper-port
             |  |     |     |           |          inet:port-number
             |  |     |     |           +--:(operator)
             |  |     |     |              +-- operator?     operator
             |  |     |     |              +-- port
             |  |     |     |                      inet:port-number
             |  |     |     +-- (destination-port)?
             |  |     |        +--:(destination-port-range-or-operator)
             |  |     |           +-- destination-port-range-or-operator
             |  |     |              +-- (port-range-or-operator)?
             |  |     |                 +--:(range)
             |  |     |                 |  +-- lower-port
             |  |     |                 |  |       inet:port-number
             |  |     |                 |  +-- upper-port
             |  |     |                 |          inet:port-number
             |  |     |                 +--:(operator)
             |  |     |                    +-- operator?     operator
             |  |     |                    +-- port
             |  |     |                            inet:port-number
             |  |     +--:(udp)
             |  |        +-- udp
             |  |           +-- length?                        uint16
             |  |           +-- (source-port)?
             |  |           |  +--:(source-port-range-or-operator)
             |  |           |     +-- source-port-range-or-operator
             |  |           |        +-- (port-range-or-operator)?
             |  |           |           +--:(range)
             |  |           |           |  +-- lower-port
             |  |           |           |  |       inet:port-number
             |  |           |           |  +-- upper-port
             |  |           |           |          inet:port-number
             |  |           |           +--:(operator)
             |  |           |              +-- operator?     operator
             |  |           |              +-- port
             |  |           |                      inet:port-number
             |  |           +-- (destination-port)?
             |  |              +--:(destination-port-range-or-operator)
             |  |                 +-- destination-port-range-or-operator
             |  |                    +-- (port-range-or-operator)?
             |  |                       +--:(range)
             |  |                       |  +-- lower-port
             |  |                       |  |       inet:port-number
             |  |                       |  +-- upper-port
             |  |                       |          inet:port-number
             |  |                       +--:(operator)
             |  |                          +-- operator?     operator
             |  |                          +-- port
             |  |                                  inet:port-number
             |  +--:(match-application)
             |     +-- match-application?   identityref
             +-- target-class-id?           string

                     Figure 4: QoS Classification Subtree

4.  Layer 2/3 VPN Common Module

   This module uses types defined in [RFC6991], [RFC8294], and
   [RFC8519].  It also uses the extension defined in [RFC8341].

   <CODE BEGINS> file "ietf-vpn-common@2022-02-11.yang"
   module ietf-vpn-common {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-vpn-common";
     prefix vpn-common;

     import ietf-netconf-acm {
       prefix nacm;
       reference
         "RFC 8341: Network Configuration Access Control Model";
     }
     import ietf-routing-types {
       prefix rt-types;
       reference
         "RFC 8294: Common YANG Data Types for the Routing Area";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types, Section 3";
     }
     import ietf-packet-fields {
       prefix packet-fields;
       reference
         "RFC 8519: YANG Data Model for Network Access
                    Control Lists (ACLs)";
     }

     organization
       "IETF OPSAWG (Operations and Management Area Working Group)";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/opsawg/>
        WG List:  <mailto:opsawg@ietf.org>

        Editor:   Mohamed Boucadair
                  <mailto:mohamed.boucadair@orange.com>
        Author:   Samier Barguil
                  <mailto:samier.barguilgiraldo.ext@telefonica.com>
        Editor:   Oscar Gonzalez de Dios
                  <mailto:oscar.gonzalezdedios@telefonica.com>
        Author:   Qin Wu
                  <mailto:bill.wu@huawei.com>";
     description
       "This YANG module defines a common module that is meant
        to be reused by various VPN-related modules (e.g., the
        Layer 3 VPN Service Model (L3SM), the Layer 2 VPN Service
        Model (L2SM), the Layer 3 VPN Network Model (L3NM), and
        the Layer 2 VPN Network Model (L2NM)).

        Copyright (c) 2022 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 9181; see the
        RFC itself for full legal notices.";

     revision 2022-02-11 {
       description
         "Initial revision.";
       reference
         "RFC 9181: A Common YANG Data Model for Layer 2 and Layer 3
                    VPNs";
     }

     /******** Collection of VPN-related features ********/
     /*
      * Features related to encapsulation schemes
      */

     feature dot1q {
       description
         "Indicates support for dot1Q encapsulation.";
       reference
         "IEEE Std 802.1Q: IEEE Standard for Local and Metropolitan
                           Area Networks--Bridges and Bridged
                           Networks";
     }

     feature qinq {
       description
         "Indicates support for QinQ encapsulation.";
       reference
         "IEEE Std 802.1ad: IEEE Standard for Local and Metropolitan
                            Area Networks---Virtual Bridged Local
                            Area Networks---Amendment 4: Provider
                            Bridges";
     }

     feature vxlan {
       description
         "Indicates support for Virtual eXtensible Local Area
          Network (VXLAN) encapsulation.";
       reference
         "RFC 7348: Virtual eXtensible Local Area Network (VXLAN):
                    A Framework for Overlaying Virtualized Layer 2
                    Networks over Layer 3 Networks";
     }

     feature qinany {
       description
         "Indicates support for QinAny encapsulation.
          The outer VLAN tag is set to a specific value, but
          the inner VLAN tag is set to any.";
     }

     feature lag-interface {
       description
         "Indicates support for Link Aggregation Groups (LAGs)
          between VPN network accesses.";
       reference
         "IEEE Std 802.1AX: IEEE Standard for Local and Metropolitan
                            Area Networks--Link Aggregation";
     }

     /*
      * Features related to multicast
      */

     feature multicast {
       description
         "Indicates support for multicast capabilities in a VPN.";
       reference
         "RFC 6513: Multicast in MPLS/BGP IP VPNs";
     }

     feature igmp {
       description
         "Indicates support for the Internet Group Management
          Protocol (IGMP).";
       reference
         "RFC 1112: Host Extensions for IP Multicasting
          RFC 2236: Internet Group Management Protocol, Version 2
          RFC 3376: Internet Group Management Protocol, Version 3";
     }

     feature mld {
       description
         "Indicates support for Multicast Listener Discovery (MLD).";
       reference
         "RFC 2710: Multicast Listener Discovery (MLD) for IPv6
          RFC 3810: Multicast Listener Discovery Version 2 (MLDv2)
                    for IPv6";
     }

     feature pim {
       description
         "Indicates support for Protocol Independent Multicast
          (PIM).";
       reference
         "RFC 7761: Protocol Independent Multicast - Sparse Mode
                    (PIM-SM): Protocol Specification (Revised)";
     }

     /*
      * Features related to address family types
      */

     feature ipv4 {
       description
         "Indicates IPv4 support in a VPN.  That is, IPv4 traffic
          can be carried in the VPN, IPv4 addresses/prefixes can
          be assigned to a VPN network access, IPv4 routes can be
          installed for the Customer Edge to Provider Edge (CE-PE)
          link, etc.";
       reference
         "RFC 791: Internet Protocol";
     }

     feature ipv6 {
       description
         "Indicates IPv6 support in a VPN.  That is, IPv6 traffic
          can be carried in the VPN, IPv6 addresses/prefixes can
          be assigned to a VPN network access, IPv6 routes can be
          installed for the CE-PE link, etc.";
       reference
         "RFC 8200: Internet Protocol, Version 6 (IPv6)
                    Specification";
     }

     /*
      * Features related to routing protocols
      */

     feature rtg-ospf {
       description
         "Indicates support for OSPF as the Provider Edge to
          Customer Edge (PE-CE) routing protocol.";
       reference
         "RFC 4577: OSPF as the Provider/Customer Edge Protocol
                    for BGP/MPLS IP Virtual Private Networks (VPNs)
          RFC 6565: OSPFv3 as a Provider Edge to Customer Edge
                    (PE-CE) Routing Protocol";
     }

     feature rtg-ospf-sham-link {
       description
         "Indicates support for OSPF sham links.";
       reference
         "RFC 4577: OSPF as the Provider/Customer Edge Protocol
                    for BGP/MPLS IP Virtual Private Networks (VPNs),
                    Section 4.2.7
          RFC 6565: OSPFv3 as a Provider Edge to Customer Edge
                    (PE-CE) Routing Protocol, Section 5";
     }

     feature rtg-bgp {
       description
         "Indicates support for BGP as the PE-CE routing protocol.";
       reference
         "RFC 4271: A Border Gateway Protocol 4 (BGP-4)";
     }

     feature rtg-rip {
       description
         "Indicates support for RIP as the PE-CE routing protocol.";
       reference
         "RFC 2453: RIP Version 2
          RFC 2080: RIPng for IPv6";
     }

     feature rtg-isis {
       description
         "Indicates support for IS-IS as the PE-CE routing
          protocol.";
       reference
         "ISO10589: Information technology - Telecommunications and
                    information exchange between systems -
                    Intermediate System to Intermediate System
                    intra-domain routeing information exchange
                    protocol for use in conjunction with the protocol
                    for providing the connectionless-mode network
                    service (ISO 8473)";
     }

     feature rtg-vrrp {
       description
         "Indicates support for the Virtual Router Redundancy
          Protocol (VRRP) in the CE-PE link.";
       reference
         "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                    Version 3 for IPv4 and IPv6";
     }

     feature bfd {
       description
         "Indicates support for Bidirectional Forwarding Detection
          (BFD) between the CE and the PE.";
       reference
         "RFC 5880: Bidirectional Forwarding Detection (BFD)";
     }

     /*
      * Features related to VPN service constraints
      */

     feature bearer-reference {
       description
         "A bearer refers to properties of the CE-PE attachment that
          are below Layer 3.
          This feature indicates support for the bearer reference
          access constraint, i.e., the reuse of a network connection
          that was already ordered to the service provider apart from
          the IP VPN site.";
     }

     feature placement-diversity {
       description
         "Indicates support for placement diversity constraints in
          the customer premises.  An example of these constraints
          may be to avoid connecting a site network access to the
          same PE as a target site network access.";
     }

     /*
      * Features related to bandwidth and Quality of Service (QoS)
      */

     feature qos {
       description
         "Indicates support for Classes of Service (CoSes) in
          the VPN.";
     }

     feature inbound-bw {
       description
         "Indicates support for the inbound bandwidth in a VPN,
          i.e., support for specifying the download bandwidth from
          the service provider network to the VPN site.  Note that
          the L3SM uses 'input' to identify the same feature.
          That terminology should be deprecated in favor of
          the terminology defined in this module.";
     }

     feature outbound-bw {
       description
         "Indicates support for the outbound bandwidth in a VPN,
          i.e., support for specifying the upload bandwidth from
          the VPN site to the service provider network.  Note that
          the L3SM uses 'output' to identify the same feature.
          That terminology should be deprecated in favor of the
          terminology defined in this module.";
     }

     /*
      * Features related to security and resilience
      */

     feature encryption {
       description
         "Indicates support for encryption in the VPN.";
     }

     feature fast-reroute {
       description
         "Indicates support for Fast Reroute (FRR) capabilities for
          a VPN site.";
     }

     /*
      * Features related to advanced VPN options
      */

     feature external-connectivity {
       description
         "Indicates support for the VPN to provide external
          connectivity (e.g., Internet, private or public cloud).";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks
                    (VPNs), Section 11";
     }

     feature extranet-vpn {
       description
         "Indicates support for extranet VPNs, i.e., the capability
          of a VPN to access a list of other VPNs.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks
                    (VPNs), Section 1.1";
     }

     feature carriers-carrier {
       description
         "Indicates support for Carriers' Carriers in VPNs.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks
                    (VPNs), Section 9";
     }

     /*
      * Identities related to address families
      */

     identity address-family {
       description
         "Defines a type for the address family.";
     }

     identity ipv4 {
       base address-family;
       description
         "Identity for an IPv4 address family.";
     }

     identity ipv6 {
       base address-family;
       description
         "Identity for an IPv6 address family.";
     }

     identity dual-stack {
       base address-family;
       description
         "Identity for IPv4 and IPv6 address families.";
     }

     /*
      * Identities related to VPN topology
      */

     identity vpn-topology {
       description
         "Base identity of the VPN topology.";
     }

     identity any-to-any {
       base vpn-topology;
       description
         "Identity for any-to-any VPN topology.  All VPN sites
          can communicate with each other without any restrictions.";
     }

     identity hub-spoke {
       base vpn-topology;
       description
         "Identity for Hub-and-Spoke VPN topology.  All Spokes can
          communicate with Hubs only and not with each other.  Hubs
          can communicate with each other.";
     }

     identity hub-spoke-disjoint {
       base vpn-topology;
       description
         "Identity for Hub-and-Spoke VPN topology where Hubs cannot
          communicate with each other.";
     }

     identity custom {
       base vpn-topology;
       description
         "Identity for custom VPN topologies where the role of the
          nodes is not strictly Hub or Spoke.  The VPN topology is
          controlled by the import/export policies.  The custom
          topology reflects more complex VPN nodes, such as a
          VPN node that acts as a Hub for certain nodes and a Spoke
          for others.";
     }

     /*
      * Identities related to network access types
      */

     identity site-network-access-type {
       description
         "Base identity for site network access types.";
     }

     identity point-to-point {
       base site-network-access-type;
       description
         "Point-to-point access type.";
     }

     identity multipoint {
       base site-network-access-type;
       description
         "Multipoint access type.";
     }

     identity irb {
       base site-network-access-type;
       description
         "Integrated Routing and Bridging (IRB).
          Identity for pseudowire connections.";
     }

     identity loopback {
       base site-network-access-type;
       description
         "Loopback access type.";
     }

     /*
      * Identities related to operational and administrative status
      */

     identity operational-status {
       description
         "Base identity for operational status.";
     }

     identity op-up {
       base operational-status;
       description
         "Operational status is Up/Enabled.";
     }

     identity op-down {
       base operational-status;
       description
         "Operational status is Down/Disabled.";
     }

     identity op-unknown {
       base operational-status;
       description
         "Operational status is Unknown.";
     }

     identity administrative-status {
       description
         "Base identity for administrative status.";
     }

     identity admin-up {
       base administrative-status;
       description
         "Administrative status is Up/Enabled.";
     }

     identity admin-down {
       base administrative-status;
       description
         "Administrative status is Down/Disabled.";
     }

     identity admin-testing {
       base administrative-status;
       description
         "Administrative status is Up for testing purposes.";
     }

     identity admin-pre-deployment {
       base administrative-status;
       description
         "Administrative status reflects a pre-deployment phase,
          i.e., prior to the actual deployment of a service.";
     }

     /*
      * Identities related to site or node roles
      */

     identity role {
       description
         "Base identity of a site or node role.";
     }

     identity any-to-any-role {
       base role;
       description
         "Any-to-any role.";
     }

     identity spoke-role {
       base role;
       description
         "A node or a site is acting as a Spoke.";
     }

     identity hub-role {
       base role;
       description
         "A node or a site is acting as a Hub.";
     }

     identity custom-role {
       base role;
       description
         "VPN node with a custom or complex role in the VPN.  For
          some sources/destinations, it can behave as a Hub, but for
          others, it can act as a Spoke, depending on the configured
          policy.";
     }

     /*
      * Identities related to VPN service constraints
      */

     identity placement-diversity {
       description
         "Base identity for access placement constraints.";
     }

     identity bearer-diverse {
       base placement-diversity;
       description
         "Bearer diversity.

          The bearers should not use common elements.";
     }

     identity pe-diverse {
       base placement-diversity;
       description
         "PE diversity.";
     }

     identity pop-diverse {
       base placement-diversity;
       description
         "Point of Presence (POP) diversity.";
     }

     identity linecard-diverse {
       base placement-diversity;
       description
         "Linecard diversity.";
     }

     identity same-pe {
       base placement-diversity;
       description
         "Having sites connected on the same PE.";
     }

     identity same-bearer {
       base placement-diversity;
       description
         "Having sites connected using the same bearer.";
     }

     /*
      * Identities related to service types
      */

     identity service-type {
       description
         "Base identity for service types.";
     }

     identity l3vpn {
       base service-type;
       description
         "L3VPN service.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs)";
     }

     identity vpls {
       base service-type;
       description
         "Virtual Private LAN Service (VPLS).";
       reference
         "RFC 4761: Virtual Private LAN Service (VPLS) Using BGP for
                    Auto-Discovery and Signaling
          RFC 4762: Virtual Private LAN Service (VPLS) Using Label
                    Distribution Protocol (LDP) Signaling";
     }

     identity vpws {
       base service-type;
       description
         "Virtual Private Wire Service (VPWS).";
       reference
         "RFC 4664: Framework for Layer 2 Virtual Private Networks
                    (L2VPNs), Section 3.1.1";
     }

     identity vpws-evpn {
       base service-type;
       description
         "Ethernet VPN (EVPN) used to support VPWS.";
       reference
         "RFC 8214: Virtual Private Wire Service Support in
                    Ethernet VPN";
     }

     identity pbb-evpn {
       base service-type;
       description
         "Provider Backbone Bridging (PBB) EVPN service.";
       reference
         "RFC 7623: Provider Backbone Bridging Combined with
                    Ethernet VPN (PBB-EVPN)";
     }

     identity mpls-evpn {
       base service-type;
       description
         "MPLS-based EVPN service.";
       reference
         "RFC 7432: BGP MPLS-Based Ethernet VPN";
     }

     identity vxlan-evpn {
       base service-type;
       description
         "VXLAN-based EVPN service.";
       reference
         "RFC 8365: A Network Virtualization Overlay Solution Using
                    Ethernet VPN (EVPN)";
     }

     /*
      * Identities related to VPN signaling types
      */

     identity vpn-signaling-type {
       description
         "Base identity for VPN signaling types.";
     }

     identity bgp-signaling {
       base vpn-signaling-type;
       description
         "Layer 2 VPNs using BGP signaling.";
       reference
         "RFC 6624: Layer 2 Virtual Private Networks Using BGP for
                    Auto-Discovery and Signaling
          RFC 7432: BGP MPLS-Based Ethernet VPN";
     }

     identity ldp-signaling {
       base vpn-signaling-type;
       description
         "Targeted Label Distribution Protocol (LDP) signaling.";
       reference
         "RFC 5036: LDP Specification";
     }

     identity l2tp-signaling {
       base vpn-signaling-type;
       description
         "Layer Two Tunneling Protocol (L2TP) signaling.";
       reference
         "RFC 3931: Layer Two Tunneling Protocol - Version 3 (L2TPv3)";
     }

     /*
      * Identities related to routing protocols
      */

     identity routing-protocol-type {
       description
         "Base identity for routing protocol types.";
     }

     identity static-routing {
       base routing-protocol-type;
       description
         "Static routing protocol.";
     }

     identity bgp-routing {
       if-feature "rtg-bgp";
       base routing-protocol-type;
       description
         "BGP routing protocol.";
       reference
         "RFC 4271: A Border Gateway Protocol 4 (BGP-4)";
     }

     identity ospf-routing {
       if-feature "rtg-ospf";
       base routing-protocol-type;
       description
         "OSPF routing protocol.";
       reference
         "RFC 4577: OSPF as the Provider/Customer Edge Protocol
                    for BGP/MPLS IP Virtual Private Networks (VPNs)
          RFC 6565: OSPFv3 as a Provider Edge to Customer Edge
                    (PE-CE) Routing Protocol";
     }

     identity rip-routing {
       if-feature "rtg-rip";
       base routing-protocol-type;
       description
         "RIP routing protocol.";
       reference
         "RFC 2453: RIP Version 2
          RFC 2080: RIPng for IPv6";
     }

     identity isis-routing {
       if-feature "rtg-isis";
       base routing-protocol-type;
       description
         "IS-IS routing protocol.";
       reference
         "ISO10589: Information technology - Telecommunications and
                    information exchange between systems -
                    Intermediate System to Intermediate System
                    intra-domain routeing information exchange
                    protocol for use in conjunction with the protocol
                    for providing the connectionless-mode network
                    service (ISO 8473)";
     }

     identity vrrp-routing {
       if-feature "rtg-vrrp";
       base routing-protocol-type;
       description
         "VRRP protocol.

          This is to be used when LANs are directly connected to
          PEs.";
       reference
         "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                    Version 3 for IPv4 and IPv6";
     }

     identity direct-routing {
       base routing-protocol-type;
       description
         "Direct routing.

          This is to be used when LANs are directly connected to PEs
          and must be advertised in the VPN.";
     }

     identity any-routing {
       base routing-protocol-type;
       description
         "Any routing protocol.

          For example, this can be used to set policies that apply
          to any routing protocol in place.";
     }

     identity isis-level {
       if-feature "rtg-isis";
       description
         "Base identity for the IS-IS level.";
       reference
         "ISO10589: Information technology - Telecommunications and
                    information exchange between systems -
                    Intermediate System to Intermediate System
                    intra-domain routeing information exchange
                    protocol for use in conjunction with the protocol
                    for providing the connectionless-mode network
                    service (ISO 8473)";
     }

     identity level-1 {
       base isis-level;
       description
         "IS-IS Level 1.";
     }

     identity level-2 {
       base isis-level;
       description
         "IS-IS Level 2.";
     }

     identity level-1-2 {
       base isis-level;
       description
         "IS-IS Levels 1 and 2.";
     }

     identity bfd-session-type {
       if-feature "bfd";
       description
         "Base identity for the BFD session type.";
     }

     identity classic-bfd {
       base bfd-session-type;
       description
         "Classic BFD.";
       reference
         "RFC 5880: Bidirectional Forwarding Detection (BFD)";
     }

     identity s-bfd {
       base bfd-session-type;
       description
         "Seamless BFD.";
       reference
         "RFC 7880: Seamless Bidirectional Forwarding Detection
                    (S-BFD)";
     }

     /*
      * Identities related to route import and export policies
      */

     identity ie-type {
       description
         "Base identity for import/export routing profiles.
          These profiles can be reused between VPN nodes.";
     }

     identity import {
       base ie-type;
       description
         "Import routing profile.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks
                    (VPNs), Section 4.3.1";
     }

     identity export {
       base ie-type;
       description
         "Export routing profile.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks
                    (VPNs), Section 4.3.1";
     }

     identity import-export {
       base ie-type;
       description
         "Import/export routing profile.";
     }

     /*
      * Identities related to bandwidth and QoS
      */

     identity bw-direction {
       description
         "Base identity for the bandwidth direction.";
     }

     identity inbound-bw {
       if-feature "inbound-bw";
       base bw-direction;
       description
         "Inbound bandwidth.";
     }

     identity outbound-bw {
       if-feature "outbound-bw";
       base bw-direction;
       description
         "Outbound bandwidth.";
     }

     identity bw-type {
       description
         "Base identity for the bandwidth type.";
     }

     identity bw-per-cos {
       if-feature "qos";
       base bw-type;
       description
         "The bandwidth is per CoS.";
     }

     identity bw-per-port {
       base bw-type;
       description
         "The bandwidth is per a given site network access.";
     }

     identity bw-per-site {
       base bw-type;
       description
         "The bandwidth is per site.  It is applicable to all the
          site network accesses within a site.";
     }

     identity bw-per-service {
       base bw-type;
       description
         "The bandwidth is per VPN service.";
     }

     identity qos-profile-direction {
       if-feature "qos";
       description
         "Base identity for the QoS profile direction.";
     }

     identity site-to-wan {
       base qos-profile-direction;
       description
         "From the customer site to the provider's network.
          This is typically the CE-to-PE direction.";
     }

     identity wan-to-site {
       base qos-profile-direction;
       description
         "From the provider's network to the customer site.
          This is typically the PE-to-CE direction.";
     }

     identity both {
       base qos-profile-direction;
       description
         "Both the WAN-to-site direction and the site-to-WAN
          direction.";
     }

     /*
      * Identities related to underlay transport instances
      */

     identity transport-instance-type {
       description
         "Base identity for underlay transport instance types.";
     }

     identity virtual-network {
       base transport-instance-type;
       description
         "Virtual network.";
       reference
         "RFC 8453: Framework for Abstraction and Control of TE
                    Networks (ACTN)";
     }

     identity enhanced-vpn {
       base transport-instance-type;
       description
         "Enhanced VPN (VPN+).  VPN+ is an approach that is
          based on existing VPN and Traffic Engineering (TE)
          technologies but adds characteristics that specific
          services require over and above classical VPNs.";
       reference
         "draft-ietf-teas-enhanced-vpn-09:
            A Framework for Enhanced Virtual Private Network
            (VPN+) Services";
     }

     identity ietf-network-slice {
       base transport-instance-type;
       description
         "IETF network slice.  An IETF network slice
          is a logical network topology connecting a number of
          endpoints using a set of shared or dedicated network
          resources that are used to satisfy specific service
          objectives.";
       reference
         "draft-ietf-teas-ietf-network-slices-05:
            Framework for IETF Network Slices";
     }

     /*
      * Identities related to protocol types.  These types are
      * typically used to identify the underlay transport.
      */

     identity protocol-type {
       description
         "Base identity for protocol types.";
     }

     identity ip-in-ip {
       base protocol-type;
       description
         "Transport is based on IP in IP.";
       reference
         "RFC 2003: IP Encapsulation within IP
          RFC 2473: Generic Packet Tunneling in IPv6 Specification";
     }

     identity ip-in-ipv4 {
       base ip-in-ip;
       description
         "Transport is based on IP over IPv4.";
       reference
         "RFC 2003: IP Encapsulation within IP";
     }

     identity ip-in-ipv6 {
       base ip-in-ip;
       description
         "Transport is based on IP over IPv6.";
       reference
         "RFC 2473: Generic Packet Tunneling in IPv6 Specification";
     }

     identity gre {
       base protocol-type;
       description
         "Transport is based on Generic Routing Encapsulation
          (GRE).";
       reference
         "RFC 1701: Generic Routing Encapsulation (GRE)
          RFC 1702: Generic Routing Encapsulation over IPv4 networks
          RFC 7676: IPv6 Support for Generic Routing Encapsulation
                    (GRE)";
     }

     identity gre-v4 {
       base gre;
       description
         "Transport is based on GRE over IPv4.";
       reference
         "RFC 1702: Generic Routing Encapsulation over IPv4
                    networks";
     }

     identity gre-v6 {
       base gre;
       description
         "Transport is based on GRE over IPv6.";
       reference
         "RFC 7676: IPv6 Support for Generic Routing Encapsulation
                    (GRE)";
     }

     identity vxlan-trans {
       base protocol-type;
       description
         "Transport is based on VXLANs.";
       reference
         "RFC 7348: Virtual eXtensible Local Area Network (VXLAN):
                    A Framework for Overlaying Virtualized Layer 2
                    Networks over Layer 3 Networks";
     }

     identity geneve {
       base protocol-type;
       description
         "Transport is based on Generic Network Virtualization
          Encapsulation (Geneve).";
       reference
         "RFC 8926: Geneve: Generic Network Virtualization
                    Encapsulation";
     }

     identity ldp {
       base protocol-type;
       description
         "Transport is based on LDP.";
       reference
         "RFC 5036: LDP Specification";
     }

     identity mpls-in-udp {
       base protocol-type;
       description
         "Transport is based on MPLS in UDP.";
       reference
         "RFC 7510: Encapsulating MPLS in UDP";
     }

     identity sr {
       base protocol-type;
       description
         "Transport is based on Segment Routing (SR).";
       reference
         "RFC 8660: Segment Routing with the MPLS Data Plane
          RFC 8663: MPLS Segment Routing over IP
          RFC 8754: IPv6 Segment Routing Header (SRH)";
     }

     identity sr-mpls {
       base sr;
       description
         "Transport is based on SR with the MPLS data plane.";
       reference
         "RFC 8660: Segment Routing with the MPLS Data Plane";
     }

     identity srv6 {
       base sr;
       description
         "Transport is based on SR over IPv6.";
       reference
         "RFC 8754: IPv6 Segment Routing Header (SRH)";
     }

     identity sr-mpls-over-ip {
       base sr;
       description
         "Transport is based on SR over MPLS over IP.";
       reference
         "RFC 8663: MPLS Segment Routing over IP";
     }

     identity rsvp-te {
       base protocol-type;
       description
         "Transport setup relies upon RSVP-TE.";
       reference
         "RFC 3209: RSVP-TE: Extensions to RSVP for LSP Tunnels";
     }

     identity bgp-lu {
       base protocol-type;
       description
         "Transport setup relies upon BGP-based labeled prefixes.";
       reference
         "RFC 8277: Using BGP to Bind MPLS Labels to Address Prefixes";
     }

     identity unknown {
       base protocol-type;
       description
         "Unknown protocol type.";
     }

     /*
      * Identities related to encapsulation types
      */

     identity encapsulation-type {
       description
         "Base identity for encapsulation types.";
     }

     identity priority-tagged {
       base encapsulation-type;
       description
         "Priority-tagged interface.";
     }

     identity dot1q {
       if-feature "dot1q";
       base encapsulation-type;
       description
         "dot1Q encapsulation.";
     }

     identity qinq {
       if-feature "qinq";
       base encapsulation-type;
       description
         "QinQ encapsulation.";
     }

     identity qinany {
       if-feature "qinany";
       base encapsulation-type;
       description
         "QinAny encapsulation.";
     }

     identity vxlan {
       if-feature "vxlan";
       base encapsulation-type;
       description
         "VXLAN encapsulation.";
     }

     identity ethernet-type {
       base encapsulation-type;
       description
         "Ethernet encapsulation type.";
     }

     identity vlan-type {
       base encapsulation-type;
       description
         "VLAN encapsulation type.";
     }

     identity untagged-int {
       base encapsulation-type;
       description
         "Untagged interface type.";
     }

     identity tagged-int {
       base encapsulation-type;
       description
         "Tagged interface type.";
     }

     identity lag-int {
       if-feature "lag-interface";
       base encapsulation-type;
       description
         "LAG interface type.";
     }

     /*
      * Identities related to VLAN tags
      */

     identity tag-type {
       description
         "Base identity for VLAN tag types.";
     }

     identity c-vlan {
       base tag-type;
       description
         "Indicates a Customer VLAN (C-VLAN) tag, normally using
          the 0x8100 Ethertype.";
     }

     identity s-vlan {
       base tag-type;
       description
         "Indicates a Service VLAN (S-VLAN) tag.";
     }

     identity s-c-vlan {
       base tag-type;
       description
         "Uses both an S-VLAN tag and a C-VLAN tag.";
     }

     /*
      * Identities related to VXLANs
      */

     identity vxlan-peer-mode {
       if-feature "vxlan";
       description
         "Base identity for VXLAN peer modes.";
     }

     identity static-mode {
       base vxlan-peer-mode;
       description
         "VXLAN access in the static mode.";
     }

     identity bgp-mode {
       base vxlan-peer-mode;
       description
         "VXLAN access by BGP EVPN learning.";
     }

     /*
      * Identities related to multicast
      */

     identity multicast-gp-address-mapping {
       if-feature "multicast";
       description
         "Base identity for multicast group mapping types.";
     }

     identity static-mapping {
       base multicast-gp-address-mapping;
       description
         "Static mapping, i.e., an interface is attached to the
          multicast group as a static member.";
     }

     identity dynamic-mapping {
       base multicast-gp-address-mapping;
       description
         "Dynamic mapping, i.e., an interface is added to the
          multicast group as a result of snooping.";
     }

     identity multicast-tree-type {
       if-feature "multicast";
       description
         "Base identity for multicast tree types.";
     }

     identity ssm-tree-type {
       base multicast-tree-type;
       description
         "Source-Specific Multicast (SSM) tree type.";
     }

     identity asm-tree-type {
       base multicast-tree-type;
       description
         "Any-Source Multicast (ASM) tree type.";
     }

     identity bidir-tree-type {
       base multicast-tree-type;
       description
         "Bidirectional tree type.";
     }

     identity multicast-rp-discovery-type {
       if-feature "multicast";
       description
         "Base identity for Rendezvous Point (RP) discovery types.";
     }

     identity auto-rp {
       base multicast-rp-discovery-type;
       description
         "Auto-RP discovery type.";
     }

     identity static-rp {
       base multicast-rp-discovery-type;
       description
         "Static type.";
     }

     identity bsr-rp {
       base multicast-rp-discovery-type;
       description
         "Bootstrap Router (BSR) discovery type.";
     }

     identity group-management-protocol {
       if-feature "multicast";
       description
         "Base identity for multicast group management protocols.";
     }

     identity igmp-proto {
       base group-management-protocol;
       description
         "IGMP.";
       reference
         "RFC 1112: Host Extensions for IP Multicasting
          RFC 2236: Internet Group Management Protocol, Version 2
          RFC 3376: Internet Group Management Protocol, Version 3";
     }

     identity mld-proto {
       base group-management-protocol;
       description
         "MLD.";
       reference
         "RFC 2710: Multicast Listener Discovery (MLD) for IPv6
          RFC 3810: Multicast Listener Discovery Version 2 (MLDv2)
                    for IPv6";
     }

     identity pim-proto {
       if-feature "pim";
       base routing-protocol-type;
       description
         "PIM.";
       reference
         "RFC 7761: Protocol Independent Multicast - Sparse Mode
                    (PIM-SM): Protocol Specification (Revised)";
     }

     identity igmp-version {
       if-feature "igmp";
       description
         "Base identity for indicating the IGMP version.";
     }

     identity igmpv1 {
       base igmp-version;
       description
         "IGMPv1.";
       reference
         "RFC 1112: Host Extensions for IP Multicasting";
     }

     identity igmpv2 {
       base igmp-version;
       description
         "IGMPv2.";
       reference
         "RFC 2236: Internet Group Management Protocol, Version 2";
     }

     identity igmpv3 {
       base igmp-version;
       description
         "IGMPv3.";
       reference
         "RFC 3376: Internet Group Management Protocol, Version 3";
     }

     identity mld-version {
       if-feature "mld";
       description
         "Base identity for indicating the MLD version.";
     }

     identity mldv1 {
       base mld-version;
       description
         "MLDv1.";
       reference
         "RFC 2710: Multicast Listener Discovery (MLD) for IPv6";
     }

     identity mldv2 {
       base mld-version;
       description
         "MLDv2.";
       reference
         "RFC 3810: Multicast Listener Discovery Version 2 (MLDv2)
                    for IPv6";
     }

     /*
      * Identities related to traffic types
      */

     identity tf-type {
       description
         "Base identity for traffic types.";
     }

     identity multicast-traffic {
       base tf-type;
       description
         "Multicast traffic.";
     }

     identity broadcast-traffic {
       base tf-type;
       description
         "Broadcast traffic.";
     }

     identity unknown-unicast-traffic {
       base tf-type;
       description
         "Unknown unicast traffic.";
     }

     /*
      * Identities related to customer applications
      */

     identity customer-application {
       description
         "Base identity for customer applications.";
     }

     identity web {
       base customer-application;
       description
         "Web applications (e.g., HTTP, HTTPS).";
     }

     identity mail {
       base customer-application;
       description
         "Mail application.";
     }

     identity file-transfer {
       base customer-application;
       description
         "File transfer application (e.g., FTP, Secure FTP (SFTP)).";
     }

     identity database {
       base customer-application;
       description
         "Database application.";
     }

     identity social {
       base customer-application;
       description
         "Social-network application.";
     }

     identity games {
       base customer-application;
       description
         "Gaming application.";
     }

     identity p2p {
       base customer-application;
       description
         "Peer-to-peer application.";
     }

     identity network-management {
       base customer-application;
       description
         "Management application (e.g., Telnet, syslog, SNMP).";
     }

     identity voice {
       base customer-application;
       description
         "Voice application.";
     }

     identity video {
       base customer-application;
       description
         "Video-conference application.";
     }

     identity embb {
       base customer-application;
       description
         "Enhanced Mobile Broadband (eMBB) application.
          Note that eMBB applications demand network performance
          with a wide variety of such characteristics as data rate,
          latency, loss rate, reliability, and many other
          parameters.";
     }

     identity urllc {
       base customer-application;
       description
         "Ultra-Reliable and Low Latency Communications (URLLC)
          application.  Note that URLLC applications demand
          network performance with a wide variety of such
          characteristics as latency, reliability, and many other
          parameters.";
     }

     identity mmtc {
       base customer-application;
       description
         "Massive Machine Type Communications (mMTC) application.
          Note that mMTC applications demand network performance
          with a wide variety of such characteristics as data rate,
          latency, loss rate, reliability, and many other
          parameters.";
     }

     /*
      * Identities related to service bundling
      */

     identity bundling-type {
       description
         "The base identity for the bundling type.  It supports a
          subset or all Customer Edge VLAN IDs (CE-VLAN IDs)
          associated with an L2VPN service.";
     }

     identity multi-svc-bundling {
       base bundling-type;
       description
         "Multi-service bundling, i.e., multiple CE-VLAN IDs
          can be associated with an L2VPN service at a site.";
     }

     identity one2one-bundling {
       base bundling-type;
       description
         "One-to-one service bundling, i.e., each L2VPN can
          be associated with only one CE-VLAN ID at a site.";
     }

     identity all2one-bundling {
       base bundling-type;
       description
         "All-to-one bundling, i.e., all CE-VLAN IDs are mapped
          to one L2VPN service.";
     }

     /*
      * Identities related to Ethernet services
      */

     identity control-mode {
       description
         "Base identity for the type of control mode used with the
          Layer 2 Control Protocol (L2CP).";
     }

     identity peer {
       base control-mode;
       description
         "'peer' mode, i.e., participate in the protocol towards
          the CE.  Peering is common for the Link Aggregation Control
          Protocol (LACP) and the Ethernet Local Management Interface
          (E-LMI) and, occasionally, for the Link Layer Discovery
          Protocol (LLDP).  For VPLSs and VPWSs, the subscriber can
          also request that the peer service provider enable
          spanning tree.";
     }

     identity tunnel {
       base control-mode;
       description
         "'tunnel' mode, i.e., pass to the egress or destination
          site.  For Ethernet Private Lines (EPLs), the expectation
          is that L2CP frames are tunneled.";
     }

     identity discard {
       base control-mode;
       description
         "'Discard' mode, i.e., discard the frame.";
     }

     identity neg-mode {
       description
         "Base identity for the type of negotiation mode.";
     }

     identity full-duplex {
       base neg-mode;
       description
         "Full-duplex negotiation mode.";
     }

     identity auto-neg {
       base neg-mode;
       description
         "Auto-negotiation mode.";
     }

     /******** VPN-related type ********/

     typedef vpn-id {
       type string;
       description
         "Defines an identifier that is used with a VPN module.
          For example, this can be a service identifier, a node
          identifier, etc.";
     }

     /******* VPN-related reusable groupings *******/

     grouping vpn-description {
       description
         "Provides common VPN information.";
       leaf vpn-id {
         type vpn-common:vpn-id;
         description
           "A VPN identifier that uniquely identifies a VPN.
            This identifier has a local meaning, e.g., within
            a service provider network.";
       }
       leaf vpn-name {
         type string;
         description
           "Used to associate a name with the service
            in order to facilitate the identification of
            the service.";
       }
       leaf vpn-description {
         type string;
         description
           "Textual description of a VPN.";
       }
       leaf customer-name {
         type string;
         description
           "Name of the customer that actually uses the VPN.";
       }
     }

     grouping vpn-profile-cfg {
       description
         "Grouping for VPN profile configuration.";
       container valid-provider-identifiers {
         description
           "Container for valid provider profile identifiers.";
         list external-connectivity-identifier {
           if-feature "external-connectivity";
           key "id";
           description
             "List of profile identifiers that uniquely identify
              profiles governing how external connectivity is
              provided to a VPN.  A profile indicates the type of
              external connectivity (Internet, cloud, etc.), the
              sites/nodes that are associated with a connectivity
              profile, etc.  A profile can also indicate filtering
              rules and/or address translation rules.  Such features
              may involve PE, P, or dedicated nodes as a function
              of the deployment.";
           leaf id {
             type string;
             description
               "Identification of an external connectivity profile.
                The profile only has significance within the service
                provider's administrative domain.";
           }
         }
         list encryption-profile-identifier {
           key "id";
           description
             "List of encryption profile identifiers.";
           leaf id {
             type string;
             description
               "Identification of the encryption profile to be used.
                The profile only has significance within the service
                provider's administrative domain.";
           }
         }
         list qos-profile-identifier {
           key "id";
           description
             "List of QoS profile identifiers.";
           leaf id {
             type string;
             description
               "Identification of the QoS profile to be used.  The
                profile only has significance within the service
                provider's administrative domain.";
           }
         }
         list bfd-profile-identifier {
           key "id";
           description
             "List of BFD profile identifiers.";
           leaf id {
             type string;
             description
               "Identification of the BFD profile to be used.  The
                profile only has significance within the service
                provider's administrative domain.";
           }
         }
         list forwarding-profile-identifier {
           key "id";
           description
             "List of forwarding profile identifiers.";
           leaf id {
             type string;
             description
               "Identification of the forwarding profile to be used.
                The profile only has significance within the service
                provider's administrative domain.";
           }
         }
         list routing-profile-identifier {
           key "id";
           description
             "List of routing profile identifiers.";
           leaf id {
             type string;
             description
               "Identification of the routing profile to be used by
                the routing protocols within sites, VPN network
                accesses, or VPN nodes for referring to VRF's
                import/export policies.

                The profile only has significance within the service
                provider's administrative domain.";
           }
         }
         nacm:default-deny-write;
       }
     }

     grouping oper-status-timestamp {
       description
         "This grouping defines some operational parameters for the
          service.";
       leaf status {
         type identityref {
           base operational-status;
         }
         config false;
         description
           "Operational status.";
       }
       leaf last-change {
         type yang:date-and-time;
         config false;
         description
           "Indicates the actual date and time of the service status
            change.";
       }
     }

     grouping service-status {
       description
         "Service status grouping.";
       container status {
         description
           "Service status.";
         container admin-status {
           description
             "Administrative service status.";
           leaf status {
             type identityref {
               base administrative-status;
             }
             description
               "Administrative service status.";
           }
           leaf last-change {
             type yang:date-and-time;
             description
               "Indicates the actual date and time of the service
                status change.";
           }
         }
         container oper-status {
           config false;
           description
             "Operational service status.";
           uses oper-status-timestamp;
         }
       }
     }

     grouping underlay-transport {
       description
         "This grouping defines the type of underlay transport for
          the VPN service or how that underlay is set.  It can
          include an identifier for an abstract transport instance to
          which the VPN is grafted or indicate a technical
          implementation that is expressed as an ordered list of
          protocols.";
       choice type {
         description
           "A choice based on the type of underlay transport
            constraints.";
         case abstract {
           description
             "Indicates that the transport constraint is an abstract
              concept.";
           leaf transport-instance-id {
             type string;
             description
               "An optional identifier of the abstract transport
                instance.";
           }
           leaf instance-type {
             type identityref {
               base transport-instance-type;
             }
             description
               "Indicates a transport instance type.  For example,
                it can be a VPN+, an IETF network slice, a virtual
                network, etc.";
           }
         }
         case protocol {
           description
             "Indicates a list of protocols.";
           leaf-list protocol {
             type identityref {
               base protocol-type;
             }
             ordered-by user;
             description
               "A client-ordered list of transport protocols.";
           }
         }
       }
     }

     grouping vpn-route-targets {
       description
         "A grouping that specifies Route Target (RT) import/export
          rules used in a BGP-enabled VPN.";
       reference
         "RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs)
          RFC 4664: Framework for Layer 2 Virtual Private Networks
                    (L2VPNs)";
       list vpn-target {
         key "id";
         description
           "RTs.  AND/OR operations may be defined based on the
            assigned RTs.";
         leaf id {
           type uint8;
           description
             "Identifies each VPN target.";
         }
         list route-targets {
           key "route-target";
           description
             "List of RTs.";
           leaf route-target {
             type rt-types:route-target;
             description
               "Conveys an RT value.";
           }
         }
         leaf route-target-type {
           type rt-types:route-target-type;
           mandatory true;
           description
             "Import/export type of the RT.";
         }
       }
       container vpn-policies {
         description
           "VPN service policies.  'vpn-policies' contains references
            to the import and export policies to be associated with
            the VPN service.";
         leaf import-policy {
           type string;
           description
             "Identifies the import policy.";
         }
         leaf export-policy {
           type string;
           description
             "Identifies the export policy.";
         }
       }
     }

     grouping route-distinguisher {
       description
         "Grouping for Route Distinguishers (RDs).";
       choice rd-choice {
         description
           "RD choice between several options for providing the RD
            value.";
         case directly-assigned {
           description
             "Explicitly assigns an RD value.";
           leaf rd {
             type rt-types:route-distinguisher;
             description
               "Indicates an RD value that is explicitly assigned.";
           }
         }
         case directly-assigned-suffix {
           description
             "The value of the Assigned Number subfield of the RD.
              The Administrator subfield of the RD will be
              based on other configuration information such as the
              Router ID or Autonomous System Number (ASN).";
           leaf rd-suffix {
             type uint16;
             description
               "Indicates the value of the Assigned Number
                subfield that is explicitly assigned.";
           }
         }
         case auto-assigned {
           description
             "The RD is auto-assigned.";
           container rd-auto {
             description
               "The RD is auto-assigned.";
             choice auto-mode {
               description
                 "Indicates the auto-assignment mode.  The RD can be
                  automatically assigned with or without
                  indicating a pool from which the RD should be
                  taken.

                  For both cases, the server will auto-assign an RD
                  value 'auto-assigned-rd' and use that value
                  operationally.";
               case from-pool {
                 leaf rd-pool-name {
                   type string;
                   description
                     "The auto-assignment will be made from the pool
                      identified by 'rd-pool-name'.";
                 }
               }
               case full-auto {
                 leaf auto {
                   type empty;
                   description
                     "Indicates that an RD is fully auto-assigned.";
                 }
               }
             }
             leaf auto-assigned-rd {
               type rt-types:route-distinguisher;
               config false;
               description
                 "The value of the auto-assigned RD.";
             }
           }
         }
         case auto-assigned-suffix {
           description
             "The value of the Assigned Number subfield will be
              auto-assigned.  The Administrator subfield will be
              based on other configuration information such as the
              Router ID or ASN.";
           container rd-auto-suffix {
             description
               "The Assigned Number subfield is auto-assigned.";
             choice auto-mode {
               description
                 "Indicates the auto-assignment mode of the
                  Assigned Number subfield.  This number can be
                  automatically assigned with or without indicating a
                  pool from which the value should be taken.

                  For both cases, the server will auto-assign
                  'auto-assigned-rd-suffix' and use that value to
                  build the RD that will be used operationally.";
               case from-pool {
                 leaf rd-pool-name {
                   type string;
                   description
                     "The assignment will be made from the pool
                      identified by 'rd-pool-name'.";
                 }
               }
               case full-auto {
                 leaf auto {
                   type empty;
                   description
                     "Indicates that the Assigned Number subfield is
                      fully auto-assigned.";
                 }
               }
             }
             leaf auto-assigned-rd-suffix {
               type uint16;
               config false;
               description
                 "Includes the value of the Assigned Number subfield
                  that is auto-assigned.";
             }
           }
         }
         case no-rd {
           description
             "Uses the 'empty' type to indicate that the RD has no
              value and is not to be auto-assigned.";
           leaf no-rd {
             type empty;
             description
               "No RD is assigned.";
           }
         }
       }
     }

     grouping vpn-components-group {
       description
         "Grouping definition to assign group IDs to associate
          VPN nodes, sites, or network accesses.";
       container groups {
         description
           "Lists the groups to which a VPN node, a site, or a
            network access belongs.";
         list group {
           key "group-id";
           description
             "List of group IDs.";
           leaf group-id {
             type string;
             description
               "The group ID to which a VPN node, a site, or a
                network access belongs.";
           }
         }
       }
     }

     grouping placement-constraints {
       description
         "Constraints related to placement of a network access.";
       list constraint {
         key "constraint-type";
         description
           "List of constraints.";
         leaf constraint-type {
           type identityref {
             base placement-diversity;
           }
           description
             "Diversity constraint type.";
         }
         container target {
           description
             "The constraint will apply against this list of
              groups.";
           choice target-flavor {
             description
               "Choice for the group definition.";
             case id {
               list group {
                 key "group-id";
                 description
                   "List of groups.";
                 leaf group-id {
                   type string;
                   description
                     "The constraint will apply against this
                      particular group ID.";
                 }
               }
             }
             case all-accesses {
               leaf all-other-accesses {
                 type empty;
                 description
                   "The constraint will apply against all other
                    network accesses of a site.";
               }
             }
             case all-groups {
               leaf all-other-groups {
                 type empty;
                 description
                   "The constraint will apply against all other
                    groups managed by the customer.";
               }
             }
           }
         }
       }
     }

     grouping ports {
       description
         "Choice of specifying source or destination port numbers.";
       choice source-port {
         description
           "Choice of specifying the source port or referring to a
            group of source port numbers.";
         container source-port-range-or-operator {
           description
             "Source port definition.";
           uses packet-fields:port-range-or-operator;
         }
       }
       choice destination-port {
         description
           "Choice of specifying a destination port or referring to a
            group of destination port numbers.";
         container destination-port-range-or-operator {
           description
             "Destination port definition.";
           uses packet-fields:port-range-or-operator;
         }
       }
     }

     grouping qos-classification-policy {
       description
         "Configuration of the traffic classification policy.";
       list rule {
         key "id";
         ordered-by user;
         description
           "List of marking rules.";
         leaf id {
           type string;
           description
             "An identifier of the QoS classification policy rule.";
         }
         choice match-type {
           default "match-flow";
           description
             "Choice for classification.";
           case match-flow {
             choice l3 {
               description
                 "Either IPv4 or IPv6.";
               container ipv4 {
                 description
                   "Rule set that matches the IPv4 header.";
                 uses packet-fields:acl-ip-header-fields;
                 uses packet-fields:acl-ipv4-header-fields;
               }
               container ipv6 {
                 description
                   "Rule set that matches the IPv6 header.";
                 uses packet-fields:acl-ip-header-fields;
                 uses packet-fields:acl-ipv6-header-fields;
               }
             }
             choice l4 {
               description
                 "Includes Layer-4-specific information.
                  This version focuses on TCP and UDP.";
               container tcp {
                 description
                   "Rule set that matches the TCP header.";
                 uses packet-fields:acl-tcp-header-fields;
                 uses ports;
               }
               container udp {
                 description
                   "Rule set that matches the UDP header.";
                 uses packet-fields:acl-udp-header-fields;
                 uses ports;
               }
             }
           }
           case match-application {
             leaf match-application {
               type identityref {
                 base customer-application;
               }
               description
                 "Defines the application to match.";
             }
           }
         }
         leaf target-class-id {
           type string;
           description
             "Identification of the class of service.  This
              identifier is internal to the administration.";
         }
       }
     }
   }
   <CODE ENDS>

5.  Security Considerations

   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.

   The "ietf-vpn-common" module defines a set of identities, types, and
   groupings.  These nodes are intended to be reused by other YANG
   modules.  The module by itself does not expose any data nodes that
   are writable, data nodes that contain read-only state, or RPCs.  As
   such, there are no additional security issues related to the "ietf-
   vpn-common" module that need to be considered.

   Modules that use the groupings that are defined in this document
   should identify the corresponding security considerations.  For
   example, reusing some of these groupings will expose privacy-related
   information (e.g., 'customer-name').  Disclosing such information may
   be considered a violation of the customer-provider trust
   relationship.

6.  IANA Considerations

   IANA has registered the following URI in the "ns" subregistry within
   the "IETF XML Registry" [RFC3688]:

   URI:  urn:ietf:params:xml:ns:yang:ietf-vpn-common
   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" subregistry [RFC6020] within the "YANG Parameters" registry.

   Name:  ietf-vpn-common
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-vpn-common
   Maintained by IANA?  N
   Prefix:  vpn-common
   Reference:  RFC 9181

7.  References

7.1.  Normative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8294]  Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger,
              "Common YANG Data Types for the Routing Area", RFC 8294,
              DOI 10.17487/RFC8294, December 2017,
              <https://www.rfc-editor.org/info/rfc8294>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

7.2.  Informative References

   [ACTN-VN-YANG]
              Lee, Y., Ed., Dhody, D., Ed., Ceccarelli, D., Bryskin, I.,
              and B. Yoon, "A YANG Data Model for VN Operation", Work in
              Progress, Internet-Draft, draft-ietf-teas-actn-vn-yang-13,
              23 October 2021, <https://datatracker.ietf.org/doc/html/
              draft-ietf-teas-actn-vn-yang-13>.

   [Enhanced-VPN-Framework]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Network (VPN+)
              Services", Work in Progress, Internet-Draft, draft-ietf-
              teas-enhanced-vpn-09, 25 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              enhanced-vpn-09>.

   [IEEE802.1ad]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks---Virtual Bridged Local Area Networks---Amendment
              4: Provider Bridges",
              <https://standards.ieee.org/standard/802_1ad-2005.html>.

   [IEEE802.1AX]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks--Link Aggregation",
              <https://standards.ieee.org/standard/802_1AX-2020.html>.

   [IEEE802.1Q]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks--Bridges and Bridged Networks",
              <https://standards.ieee.org/standard/802_1Q-2018.html>.

   [ISO10589] ISO, "Information technology - Telecommunications and
              information exchange between systems - Intermediate System
              to Intermediate System intra-domain routeing information
              exchange protocol for use in conjunction with the protocol
              for providing the connectionless-mode network service (ISO
              8473)", International Standard 10589:2002, Second Edition,
              November 2002, <https://www.iso.org/standard/30932.html>.

   [L2NM-YANG]
              Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
              Ed., and L. Munoz, "A Layer 2 VPN Network YANG Model",
              Work in Progress, Internet-Draft, draft-ietf-opsawg-l2nm-
              12, 22 November 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
              l2nm-12>.

   [Network-Slices-Framework]
              Farrel, A., Ed., Gray, E., Drake, J., Rokui, R., Homma,
              S., Makhijani, K., Contreras, LM., and J. Tantsura,
              "Framework for IETF Network Slices", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slices-05, 25
              October 2021, <https://datatracker.ietf.org/doc/html/
              draft-ietf-teas-ietf-network-slices-05>.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,
              <https://www.rfc-editor.org/info/rfc1112>.

   [RFC1701]  Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
              Routing Encapsulation (GRE)", RFC 1701,
              DOI 10.17487/RFC1701, October 1994,
              <https://www.rfc-editor.org/info/rfc1701>.

   [RFC1702]  Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
              Routing Encapsulation over IPv4 networks", RFC 1702,
              DOI 10.17487/RFC1702, October 1994,
              <https://www.rfc-editor.org/info/rfc1702>.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              DOI 10.17487/RFC2003, October 1996,
              <https://www.rfc-editor.org/info/rfc2003>.

   [RFC2080]  Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
              DOI 10.17487/RFC2080, January 1997,
              <https://www.rfc-editor.org/info/rfc2080>.

   [RFC2236]  Fenner, W., "Internet Group Management Protocol, Version
              2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
              <https://www.rfc-editor.org/info/rfc2236>.

   [RFC2453]  Malkin, G., "RIP Version 2", STD 56, RFC 2453,
              DOI 10.17487/RFC2453, November 1998,
              <https://www.rfc-editor.org/info/rfc2453>.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <https://www.rfc-editor.org/info/rfc2473>.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              DOI 10.17487/RFC2710, October 1999,
              <https://www.rfc-editor.org/info/rfc2710>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
              <https://www.rfc-editor.org/info/rfc3376>.

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,
              <https://www.rfc-editor.org/info/rfc3810>.

   [RFC3931]  Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
              "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
              RFC 3931, DOI 10.17487/RFC3931, March 2005,
              <https://www.rfc-editor.org/info/rfc3931>.

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026,
              DOI 10.17487/RFC4026, March 2005,
              <https://www.rfc-editor.org/info/rfc4026>.

   [RFC4176]  El Mghazli, Y., Ed., Nadeau, T., Boucadair, M., Chan, K.,
              and A. Gonguet, "Framework for Layer 3 Virtual Private
              Networks (L3VPN) Operations and Management", RFC 4176,
              DOI 10.17487/RFC4176, October 2005,
              <https://www.rfc-editor.org/info/rfc4176>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4577]  Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
              Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
              Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
              June 2006, <https://www.rfc-editor.org/info/rfc4577>.

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,
              <https://www.rfc-editor.org/info/rfc4664>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC4762]  Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
              LAN Service (VPLS) Using Label Distribution Protocol (LDP)
              Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
              <https://www.rfc-editor.org/info/rfc4762>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <https://www.rfc-editor.org/info/rfc4960>.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <https://www.rfc-editor.org/info/rfc5036>.

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <https://www.rfc-editor.org/info/rfc5798>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC6565]  Pillay-Esnault, P., Moyer, P., Doyle, J., Ertekin, E., and
              M. Lundberg, "OSPFv3 as a Provider Edge to Customer Edge
              (PE-CE) Routing Protocol", RFC 6565, DOI 10.17487/RFC6565,
              June 2012, <https://www.rfc-editor.org/info/rfc6565>.

   [RFC6624]  Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
              Virtual Private Networks Using BGP for Auto-Discovery and
              Signaling", RFC 6624, DOI 10.17487/RFC6624, May 2012,
              <https://www.rfc-editor.org/info/rfc6624>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <https://www.rfc-editor.org/info/rfc7510>.

   [RFC7623]  Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
              Henderickx, "Provider Backbone Bridging Combined with
              Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
              September 2015, <https://www.rfc-editor.org/info/rfc7623>.

   [RFC7676]  Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
              for Generic Routing Encapsulation (GRE)", RFC 7676,
              DOI 10.17487/RFC7676, October 2015,
              <https://www.rfc-editor.org/info/rfc7676>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <https://www.rfc-editor.org/info/rfc7880>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
              Rabadan, "Virtual Private Wire Service Support in Ethernet
              VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
              <https://www.rfc-editor.org/info/rfc8214>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

   [RFC8299]  Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
              "YANG Data Model for L3VPN Service Delivery", RFC 8299,
              DOI 10.17487/RFC8299, January 2018,
              <https://www.rfc-editor.org/info/rfc8299>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
              Uttaro, J., and W. Henderickx, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,
              <https://www.rfc-editor.org/info/rfc8453>.

   [RFC8466]  Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
              Data Model for Layer 2 Virtual Private Network (L2VPN)
              Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
              2018, <https://www.rfc-editor.org/info/rfc8466>.

   [RFC8512]  Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
              Vinapamula, S., and Q. Wu, "A YANG Module for Network
              Address Translation (NAT) and Network Prefix Translation
              (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
              <https://www.rfc-editor.org/info/rfc8512>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC8663]  Xu, X., Bryant, S., Farrel, A., Hassan, S., Henderickx,
              W., and Z. Li, "MPLS Segment Routing over IP", RFC 8663,
              DOI 10.17487/RFC8663, December 2019,
              <https://www.rfc-editor.org/info/rfc8663>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8926]  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
              "Geneve: Generic Network Virtualization Encapsulation",
              RFC 8926, DOI 10.17487/RFC8926, November 2020,
              <https://www.rfc-editor.org/info/rfc8926>.

   [RFC9182]  Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
              Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model
              for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182,
              February 2022, <https://www.rfc-editor.org/info/rfc9182>.

Appendix A.  Example of Common Data Nodes in Early L2NM/L3NM Designs

   In order to avoid duplication of data nodes and to ease passing data
   among layers (i.e., from the service layer to the network layer and
   vice versa), early versions of the L3NM reused many of the data nodes
   that are defined in the L3SM.  Nevertheless, that approach was
   abandoned because that design was interpreted as if the deployment of
   the L3NM depends on the L3SM, while this is not required.  For
   example, a service provider may decide to use the L3NM to build its
   L3VPN services without exposing the L3SM to customers.

   Likewise, early versions of the L2NM reused many of the data nodes
   that are defined in both the L2SM and the L3NM.  An example of L3NM
   groupings reused in the L2NM is shown in Figure 5.  Such reuse of
   data nodes was interpreted as if the deployment of the L2NM requires
   support for the L3NM, which is not required.

   module ietf-l2vpn-ntw {
    ...
     import ietf-l3vpn-ntw {
       prefix l3vpn-ntw;
       reference
         "RFC 9182: A YANG Network Data Model for Layer 3 VPNs";
     }
     ...
     container l2vpn-ntw {
       ...
       container vpn-services {
         list vpn-service {
           ...
           uses l3vpn-ntw:service-status;
           uses l3vpn-ntw:svc-transport-encapsulation;
           ...
         }
       }
       ...
     }
   }

                Figure 5: Excerpt from the L2NM YANG Module

Acknowledgements

   During the discussions of this work, helpful comments and reviews
   were received from (listed alphabetically) Alejandro Aguado, Raul
   Arco, Miguel Cros Cecilia, Joe Clarke, Dhruv Dhody, Adrian Farrel,
   Roque Gagliano, Christian Jacquenet, Kireeti Kompella, Julian Lucek,
   Tom Petch, Erez Segev, and Paul Sherratt.  Many thanks to them.

   This work is partially supported by the European Commission under
   Horizon 2020 Secured autonomic traffic management for a Tera of SDN
   flows (Teraflow) project (grant agreement number 101015857).

   Many thanks to Radek Krejci for the YANG Doctors review, Wesley Eddy
   for the tsvart review, Ron Bonica and Victoria Pritchard for the
   RtgDir review, Joel Halpern for the genart review, Tim Wicinski for
   the opsdir review, and Suresh Krishnan for the intdir review.

   Special thanks to Robert Wilton for the AD review.

   Thanks to Roman Danyliw, Lars Eggert, Warren Kumari, Erik Kline,
   Zaheduzzaman Sarker, Benjamin Kaduk, and Éric Vyncke for the IESG
   review.

Contributors

   Italo Busi
   Huawei Technologies

   Email: Italo.Busi@huawei.com

   Luis Angel Munoz
   Vodafone

   Email: luis-angel.munoz@vodafone.com

   Victor Lopez
   Nokia
   Madrid
   Spain

   Email: victor.lopez@nokia.com

Authors' Addresses

   Samier Barguil
   Telefonica
   Madrid
   Spain

   Email: samier.barguilgiraldo.ext@telefonica.com

   Oscar Gonzalez de Dios (editor)
   Telefonica
   Madrid
   Spain

   Email: oscar.gonzalezdedios@telefonica.com

   Mohamed Boucadair (editor)
   Orange
   France

   Email: mohamed.boucadair@orange.com

   Qin Wu
   Huawei
   101 Software Avenue
   Yuhua District
   Nanjing
   Jiangsu, 210012
   China

   Email: bill.wu@huawei.com