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A Framework for Enhanced Virtual Private Network (VPN+)

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Jie Dong , Stewart Bryant , Zhenqiang Li , Takuya Miyasaka , Young Lee
Last updated 2023-01-16 (Latest revision 2022-09-19)
Replaces draft-dong-teas-enhanced-vpn
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TEAS Working Group                                               J. Dong
Internet-Draft                                                    Huawei
Intended status: Informational                                 S. Bryant
Expires: 24 March 2023                              University of Surrey
                                                                   Z. Li
                                                            China Mobile
                                                             T. Miyasaka
                                                        KDDI Corporation
                                                                  Y. Lee
                                                       20 September 2022

        A Framework for Enhanced Virtual Private Network (VPN+)


   This document describes the framework for Enhanced Virtual Private
   Network (VPN+).  The purpose of VPN+ is to support the needs of new
   applications (e.g. low latency, bounded jitter, etc.), by utilizing
   an approach that is based on the VPN and Traffic Engineering (TE)
   technologies, and adds characteristics that specific services require
   beyond those provided by existing VPNs.  Typically, VPN+ will be used
   to underpin network slicing, but could also be of use in its own
   right providing enhanced connectivity services between customer
   sites.  This document also provides an overview of relevant
   technologies in different network layers, and identifies some areas
   for potential new work.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 24 March 2023.

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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 (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Overview of the Requirements  . . . . . . . . . . . . . . . .   7
     3.1.  Performance Guarantees  . . . . . . . . . . . . . . . . .   7
     3.2.  Isolation between VPN+ Services . . . . . . . . . . . . .   9
       3.2.1.  A Pragmatic Approach to Isolation . . . . . . . . . .  10
     3.3.  Integration with Network Resources and Functions  . . . .  11
       3.3.1.  Abstraction . . . . . . . . . . . . . . . . . . . . .  12
     3.4.  Dynamic Changes . . . . . . . . . . . . . . . . . . . . .  12
     3.5.  Customized Control  . . . . . . . . . . . . . . . . . . .  13
     3.6.  Applicability to Overlay Technologies . . . . . . . . . .  13
     3.7.  Inter-Domain and Inter-Layer Network  . . . . . . . . . .  14
   4.  The Architecture of VPN+  . . . . . . . . . . . . . . . . . .  14
     4.1.  Layered Architecture  . . . . . . . . . . . . . . . . . .  16
     4.2.  Multi-Point to Multi-Point (MP2MP) Connectivity . . . . .  18
     4.3.  Application Specific Data Types . . . . . . . . . . . . .  19
     4.4.  Scaling Considerations  . . . . . . . . . . . . . . . . .  19
   5.  Candidate Technologies  . . . . . . . . . . . . . . . . . . .  20
     5.1.  Forwarding Resource Partitioning  . . . . . . . . . . . .  20
       5.1.1.  Flexible Ethernet . . . . . . . . . . . . . . . . . .  20
       5.1.2.  Dedicated Queues  . . . . . . . . . . . . . . . . . .  21
       5.1.3.  Time Sensitive Networking . . . . . . . . . . . . . .  21
     5.2.  Data Plane Encapsulation and Forwarding . . . . . . . . .  22
       5.2.1.  Deterministic Networking  . . . . . . . . . . . . . .  22
       5.2.2.  MPLS Traffic Engineering (MPLS-TE)  . . . . . . . . .  22
       5.2.3.  Segment Routing . . . . . . . . . . . . . . . . . . .  22
     5.3.  Non-Packet Data Plane . . . . . . . . . . . . . . . . . .  23
     5.4.  Control Plane . . . . . . . . . . . . . . . . . . . . . .  23
     5.5.  Management Plane  . . . . . . . . . . . . . . . . . . . .  25
     5.6.  Applicability of Service Data Models to VPN+  . . . . . .  26
   6.  Applicability in Network Slice Realization  . . . . . . . . .  26
     6.1.  VTN Planning  . . . . . . . . . . . . . . . . . . . . . .  27

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     6.2.  VTN Instantiation . . . . . . . . . . . . . . . . . . . .  27
     6.3.  VPN+ Service Provisioning . . . . . . . . . . . . . . . .  28
     6.4.  Network Slice Traffic Steering and Forwarding . . . . . .  28
   7.  Scalability Considerations  . . . . . . . . . . . . . . . . .  28
     7.1.  Maximum Stack Depth of SR . . . . . . . . . . . . . . . .  29
     7.2.  RSVP-TE Scalability . . . . . . . . . . . . . . . . . . .  29
     7.3.  SDN Scaling . . . . . . . . . . . . . . . . . . . . . . .  30
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  30
     8.1.  OAM Considerations  . . . . . . . . . . . . . . . . . . .  30
     8.2.  Telemetry Considerations  . . . . . . . . . . . . . . . .  31
   9.  Enhanced Resiliency . . . . . . . . . . . . . . . . . . . . .  31
   10. Operational Considerations  . . . . . . . . . . . . . . . . .  32
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  32
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  33
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  34
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     15.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   Virtual Private Networks (VPNs) have served the industry well as a
   means of providing different groups of users with logically isolated
   connectivity over a common network.  The common (base) network that
   is used to provide the VPNs is often referred to as the underlay, and
   the VPN is often called an overlay.

   Customers of a network operator may request connectivity services
   with advanced characteristics such as low latency guarantees, bounded
   jitter, or isolation from other services or customers so that changes
   in some other services (e.g. changes in network load, or events such
   as congestion or outages) have no or only acceptable effect on the
   throughput or latency of the services provided to the customer.
   These services are referred to as "enhanced VPNs" (known as VPN+) in
   that they are similar to VPN services providing the customer with the
   required connectivity, but in addition they have enhanced

   The concept of network slicing has gained traction driven largely by
   needs surfacing from 5G [NGMN-NS-Concept] [TS23501] [TS28530].
   According to [TS28530], a 5G end-to-end network slice consists of
   three major types of network segments: Radio Access Network (RAN),
   Transport Network (TN), and Mobile Core Network (CN).  The transport
   network provides the connectivity between different entities in RAN
   and CN segments of a 5G end-to-end network slice, with specific
   performance commitment.

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   [I-D.ietf-teas-ietf-network-slices] defines the terminologies and the
   characteristics of IETF Network Slices.  It also discusses the
   general framework, the components and interfaces for requesting and
   operating IETF Network Slices.  An IETF Network Slice Service enables
   connectivity between a set of Service Demarcation Points (SDPs) with
   specific Service Level Objectives (SLOs) and Service Level
   Expectations (SLEs) over a common underlay network.  An IETF Network
   Slice can be realized as a logical network connecting a number of
   endpoints and is associated with a set of shared or dedicated network
   resources that are used to satisfy the Service Level Objectives
   (SLOs) and Service Level Expectations (SLEs) requirements.  In this
   document (which is solely about IETF technologies) we refer to an
   "IETF Network Slice" simply as a "network slice": a network slice is
   considered as one typical use case of VPN+.

   A network slice may involve multiple technologies (e.g.  IP or
   Optical), and may span multiple administrative domains.  Depending on
   the customer's requirements, a network slice could be isolated from
   other network slices in terms of data plane, control plane, and
   management plane resources.

   Network slicing can build on the concepts of resource management,
   network virtualization, and abstraction to provide performance
   assurance, flexibility, programmability, and modularity.  It may use
   techniques such as Software Defined Networking (SDN) [RFC7149],
   network abstraction [RFC7926], and Network Function Virtualization
   (NFV) [RFC8172] [RFC8568] to create multiple logical (virtual)
   networks, each tailored for use by a set of services or by a
   particular tenant or a group of tenants that share the same or
   similar requirements.  These logical networks are created on top of a
   common underlay network.  How the network slices are engineered is

   The requirements of VPN+ services cannot simple be met by overlay
   networks, as these services require tighter coordination and
   integration between the overlay and the underlay networks.

   In the overlay network, VPN has been defined as the network construct
   to provide the required connectivity for different services or
   customers.  In the underlay network, this document introduces the
   concept Virtual Transport Network (VTN) A VTN is a virtual underlay
   network which is associated with a network topology, and is allocated
   with a set of dedicated or shared resources from the physical
   underlay network.

   A VPN+ service is realized by integrating a VPN in the overlay and a
   VTN in the underlay.  With this, a VPN+ service can provide enhanced
   properties such as guaranteed resources and assured or predictable

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   performance.  A VPN+ service may also include a set of service
   functions.  These enhanced properties have general applicability, and
   are also of interest as part of a network slicing solution.  Hence
   VPN+ techniques can be used to instantiate a network slice service,
   and they can also be of use in general cases to provide enhanced
   connectivity services between customer sites or service end points.

   [I-D.ietf-teas-ietf-network-slices] introduces the concept Network
   Resource Partition (NRP) as a collection of resources in the underlay
   network that can reliably support specific IETF Network Slice SLAs.
   An NRP can be associated with a network topology to select or specify
   the set of links and nodes involved.  VTN and NRP are considered as
   similar concepts, and NRP can be seen as an instantiation of VTN in
   the context of network slicing.

   It is not envisaged that VPN+ services will replace VPN services.
   VPN services will continue to be delivered using existing mechanisms
   and can co-exist with VPN+ services.

   This document describes a framework for using existing, modified, and
   potential new technologies as components to provide VPN+ services.
   Specifically, this document provides:

   *  The functional requirements and service characteristics of a VPN+

   *  The design of the data plane for VPN+.

   *  The necessary control and management protocols in both the
      underlay and the overlay of VPN+.

   *  The mechanisms to achieve integration between overlay and

   *  The necessary Operation, Administration, and Management (OAM)
      methods to instrument a VPN+ to make sure that the required
      Service Level Agreement (SLA) between the customer and the network
      operator is met, and to take any corrective action (such as
      switching traffic to an alternate path) to avoid SLA violation.

   The required layered network structure to achieve these objectives is
   shown in Section 4.1.

2.  Terminology

   In this document, the relationship of the four terms "VPN", "VPN+",
   "VTN", and "Network Slice" are as follows:

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   *  A Virtual Private Network (VPN) refers to the overlay network
      service that provides connectivity between different customer
      sites, and that maintains traffic separation between different
      customers.  The typical VPN technologies are: IPVPN [RFC2764],
      L2VPN [RFC4664], L3VPN [RFC4364], and EVPN [RFC7432].

   *  An enhanced VPN (VPN+) service is an evolution of the VPN service
      that makes additional service-specific commitments.  An enhanced
      VPN is made by integrating a VPN with a set of network resources
      allocated in the underlay network.

   *  A Virtual Transport Network (VTN) is a virtual underlay network
      which is associated with a logical network topology, and is
      allocated with a set of dedicated or shared network resources from
      the physical underlay network.  A VTN has the capability of
      delivering the network resources and performance characteristics
      required by the VPN+ customers.

   *  A network slice service could be delivered by provisioning a VPN+
      service in the network.  Other mechanisms for delivering network
      slices may exist but are not in scope for this document.

   The term "tenant" is used in this document to refer to the customers
   and all of their associated VPN+ services.

   The following terms are also used in this document.  Some of them are
   newly defined, some others reference existing definitions.

   SLA:  Service Level Agreement.  See

   SLO:  Service Level Objective.  See

   SLE:  Service Level Expectation.  See

   ACTN:  Abstraction and Control of Traffic Engineered Networks

   DetNet:  Deterministic Networking.  See [DETNET] and [RFC8655]

   FlexE:  Flexible Ethernet [FLEXE]

   TSN:  Time Sensitive Networking [TSN]

   VN:  Virtual Network.  See [RFC8453]

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   VTP:  Virtual Transport Path.  A VTP is a path through the VTN which
      provides the required connectivity and performance between two or
      more customer sites.

3.  Overview of the Requirements

   This section provides an overview of the requirements of a VPN+

3.1.  Performance Guarantees

   Performance guarantees are made by network operators to their
   customers in relation to the services provided to the customers.
   They are usually expressed in SLAs as a set of SLOs.

   There are several kinds of performance guarantee, including
   guaranteed maximum packet loss, guaranteed maximum delay, and
   guaranteed delay variation.  Note that these guarantees apply to
   conformance traffic, out-of-profile traffic will be handled according
   to a separate agreement with the customer. (see for example, section
   3.6 of [RFC7297]).

   Guaranteed maximum packet loss is usually addressed by setting packet
   priorities, queue size, and discard policy.  However this becomes
   more difficult when the requirement is combined with latency
   requirements.  The limiting case is zero congestion loss, and that is
   the goal of DetNet [DETNET] and TSN [TSN].  In modern optical
   networks, loss due to transmission errors already approaches zero,
   but there is the possibility of failure of the interface or the fiber
   itself.  This type of fault can be addressed by some form of signal
   duplication and transmission over diverse paths.

   Guaranteed maximum latency is required by a number of applications
   particularly real-time control applications and some types of virtual
   reality applications.  DetNet [DETNET] is relevant, however
   additional methods of enhancing the underlay to better support the
   delay guarantees may be needed, and these methods will need to be
   integrated with the overall service provisioning mechanisms.

   Guaranteed maximum delay variation is a performance guarantee that
   may also be needed.  [RFC8578] calls up a number of cases that need
   this guarantee, for example in electrical utilities.  Time transfer
   is an example service that needs a performance guarantee, although it
   is in the nature of time that the service might be delivered by the
   underlay as a shared service and not provided through different
   VPN+s.  Alternatively, a dedicated VPN+ might be used to provide this
   as a shared service.

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   This suggests that a spectrum of service guarantees need to be
   considered when deploying a VPN+. As a guide to understanding the
   design requirements we can consider four types of service:

   *  Best effort

   *  Assured bandwidth

   *  Guaranteed latency

   *  Enhanced delivery

   The best effort service is the basic connectivity service that can be
   provided by current VPNs.

   An assured bandwidth service is a connectivity service in which the
   bandwidth over some period of time is assured.  This could be
   achieved either simply based on a best effort service with over-
   capacity provisioning, or it can be based on MPLS traffic engineered
   label switching paths (TE-LSPs) with bandwidth reservations.
   Depending on the technique used, however, the bandwidth is not
   necessarily assured at any instant.  Providing assured bandwidth to
   VPNs, for example by using per-VPN TE-LSPs, is not widely deployed at
   least partially due to scalability concerns.  The more common
   approach of aggregating multiple VPNs onto common TE-LSPs results in
   shared bandwidth and so may reduce the assurance of bandwidth to any
   one service.  VPN+ aims to provide a more scalable approach for such

   A guaranteed latency service has an upper bound to edge-to-edge
   latency.  Assuring the upper bound is sometimes more important than
   minimizing latency.  There are several new technologies that provide
   some assistance with this performance guarantee.  Firstly, the IEEE
   TSN project [TSN] introduces the concept of scheduling of delay- and
   loss-sensitive packets.  FlexE [FLEXE] is also useful to help provide
   a guaranteed upper bound to latency.  DetNet is also of relevance in
   assuring an upper bound of end-to-end packet latency in network
   layer.  The use of these technologies to deliver VPN+ services needs
   to be considered when a guaranteed latency service is required.

   An enhanced delivery service is a connectivity service in which the
   underlay network (at layer-3) needs to ensure to eliminate packet
   loss in the event of equipment or media failures.  This may be
   achieved by delivering a copy of the packet through multiple paths.
   Such a mechanism may need to be used for VPN+ service.

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3.2.  Isolation between VPN+ Services

   One element of the SLA demanded for VPN+ service may be a guarantee
   that the service offered to the customer will not be affected by any
   other traffic flows in the network.  This is termed "isolation" in
   section 3.8 of [RFC7297], and a customer may express the requirement
   for isolation as an SLE for network slice service

   One way for a network operator to meet the requirement for isolation
   is setting and conforming to all the SLOs.  For example, traffic
   congestion (interference from other services) might impact on the
   latency experienced by a VPN+ customer.  Thus, in this example,
   conformance to a latency SLO would be the primary requirement for
   delivery of the VPN+ service, and isolation from other services might
   be only a means to that end.

   Another way for a service provider to meet the isolation requirement
   is to control the degree to which traffic from one service is
   isolated from other services in the network.

   There is a fine distinction between how isolation is requested by a
   customer and how it is delivered by the service provider.  In
   general, the customer is interested in service performance and not
   how it is delivered.  Thus, for example, the customer wants specific
   quality guarantees and is not concerned about how the service
   provider delivers them.  However, it should be noted that some
   aspects of isolation might be directly measurable by a customer if
   they have information about the traffic patterns on a number services
   supported by the same service provider.  Furthermore, a customer may
   be nervous about disruption caused by other services, contamination
   by other traffic, or delivery of their traffic to the wrong
   destinations.  In this way, the customer may want to specify (and pay
   for) the level of isolation provided by the service provider.

   Isolation is achieved in the realization of a VPN+ through existing
   technologies that may be supplemented by new mechanisms.  The service
   provider chooses which processes to use to meet this SLE just as they
   choose how to meet all other SLOs and SLEs.  Isolation may be
   achieved in the network by various forms of resource partitioning
   ranging from simple separation of service traffic on delivery
   (ensuring that traffic is not delivered to the wrong customer),
   through sharing of resources with some form of safeguards, to
   dedicated allocation of resources for a specific VPN+ service.  For
   example, interference avoidance may be achieved by network capacity
   planning, allocating dedicated network resources, traffic policing or
   shaping, prioritizing in using shared network resources, etc.

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   The terms hard and soft isolation are used to indicate different
   levels of isolation within the underlay network.  A service has soft
   isolation if the traffic of one service cannot be received by the
   customers of another service.  The existing IP and MPLS VPNs are
   examples of services with soft isolation: the network delivers the
   traffic only to the required customer endpoints.  However, with soft
   isolation, as the network resources are shared, traffic from some
   services may congest the network, resulting in packet loss and delay
   for other services.  The ability for a service or a group of services
   to be sheltered from this effect is called hard isolation.  Hard
   isolation may be needed so that applications with exacting
   requirements can function correctly, despite other demands (perhaps a
   burst of traffic in another service) competing for the underlying
   resources.  A customer may request different degrees of isolation
   ranging from soft isolation to hard isolation.  In practice isolation
   may be delivered on a spectrum between soft and hard, and in some
   cases soft and hard isolation may be used in a hierarchical manner
   with one VPN+ service being built on another.

   To provide the required level of isolation, resources may need to be
   reserved in the data plane of the underlay network and dedicated to
   traffic from a specific VPN+ service or a specific group of VPN+
   services.  This may introduce scalability concerns both in the
   implementation (as each VPN+ would need to be tracked in the network)
   and in how many resources need to be reserved and may be under-used
   (see Section 4.4).  Thus, some trade-off needs to be considered to
   provide the isolation between VPN+ services while still allowing
   reasonable resource sharing.

   An optical underlay can offer a high degree of isolation, at the cost
   of allocating resources on a long-term and end-to-end basis.  On the
   other hand, where adequate isolation can be achieved at the packet
   layer, this permits the resources to be shared amongst a group of
   services and only dedicated to a service on a temporary basis.

   The next section explores a pragmatic approach to isolation in packet

3.2.1.  A Pragmatic Approach to Isolation

   A key question is whether it is possible to achieve hard isolation in
   packet networks that were designed to provide statistical
   multiplexing through sharing of data plane resources, a significant
   economic advantage when compared to a dedicated or a Time Division
   Multiplexing (TDM) network.  Clearly, there is no need for a customer
   to request more isolation than their applications require, and no
   need for a service provider to provide more isolation than requested
   by their customer, an approximation to full hard isolation is

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   sufficient in most cases when hard isolation is requested.  For
   example, pseudowires [RFC3985] emulate services that would have had
   hard isolation in their native form.

        |          \---------------v---------------/
    Statistical                Pragmatic             Absolute
    Multiplexing               Isolation            Isolation
   (Traditional VPNs)        (Enhanced VPN)     (Dedicated Network)

                    Figure 1: The Spectrum of Isolation

   Figure 1 shows a spectrum of isolation that may be delivered by a
   network.  At one end of the spectrum, we see statistical multiplexing
   technologies that support current VPNs.  This is a service type that
   has served the industry well and will continue to do so.  At the
   opposite end of the spectrum, we have the absolute isolation provided
   by dedicated transport networks.  The goal of VPN+ is "pragmatic
   isolation".  This is isolation that is better than what is obtainable
   from pure statistical multiplexing, more cost effective and flexible
   than a dedicated network, but is a practical solution that is good
   enough for the majority of applications.  Mechanisms for both soft
   isolation and hard isolation are needed to meet different levels of
   service requirements.

3.3.  Integration with Network Resources and Functions

   The way to achieve the characteristics demand of a VPN+ service (such
   as guaranteed or predictable performance) is by integrating the
   overlay VPN with a particular set of resources in the underlay
   network which are allocated to meet the service requirements.  This
   needs be done in a flexible and scalable way so that it can be widely
   deployed in operators' networks to support a good number of VPN+

   Taking mobile networks and in particular 5G into consideration, the
   integration of the network with service functions is likely a
   requirement.  The IETF's work on service function chaining (SFC)
   [SFC] provides a foundation for this.  Service functions can be
   considered as part of the VPN+ services.  The detailed mechanisms
   about the integration between service functions and VPN+ are out of
   the scope of this document.

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3.3.1.  Abstraction

   Integration of the overlay VPN and the underlay network resources and
   functions does not always need to be a direct mapping.  As described
   in [RFC7926], abstraction is the process of applying policy to a set
   of information about a traffic engineered (TE) network to produce
   selective information that represents the potential ability to
   connect across the network.  The process of abstraction presents the
   connectivity graph in a way that is independent of the underlying
   network technologies, capabilities, and topology so that the graph
   can be used to plan and deliver network services in a uniform way.

   With the approach of abstraction, VPN+ may be built on top of an
   abstracted topology that represents the connectivity capabilities of
   the underlay TE based network as described in the framework for
   Abstraction and Control of TE Networks (ACTN) [RFC8453] as discussed
   further in Section 5.5.

3.4.  Dynamic Changes

   VPN+s need to be created, modified, and removed from the network
   according to service demands.  A VPN+ that requires hard isolation
   (Section 3.2) must not be disrupted by the instantiation or
   modification of another VPN+ service.  Determining whether
   modification of an VPN+ can be disruptive to that VPN+, and whether
   the traffic in flight will be disrupted can be a difficult problem.

   Dynamic changes both to the VPN+ and to the underlay network need to
   be managed to avoid disruption to services that are sensitive to
   changes in network performance.

   In addition to non-disruptively managing the network during changes
   such as the inclusion of a new VPN+ service endpoint or a change to a
   link, VPN+ traffic might need to be moved because of changes to
   traffic patterns and volumes.  This means that during the lifetime of
   a VPN+ service, closed-loop optimization is needed so that the
   delivered service always matches the ordered service SLA.

   The data plane aspects of this problem are discussed further in
   Section 5.1, Section 5.2, and Section 5.3.

   The control plane aspects of this problem are discussed further in
   Section 5.4.

   The management plane aspects of this problem are discussed further in
   Section 5.5.

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3.5.  Customized Control

   In many cases the customers are delivered with VPN+ services without
   knowing the information about the underlying VTNs.  However,
   depending on the agreement between the operator and the customer, in
   some cases the customer may also be provided with some information
   about the underlying VTNs.  Such information can be filtered or
   aggregated according to the operator's policy.  This allows the
   customer of the VPN+ to have some visibility and even control over
   how the underlying topology and resources of the VTN are used.  For
   example, the customers may be able to specify the path or path
   constraints within the VTN for specific traffic flows of their VPN+
   service.  Depending on the requirements, an VPN+ customer may have
   his/her own network controller, which may be provided with an
   interface to the control or management system run by the network
   operator.  Note that such control is within the scope of the
   customer's VPN+ service, any additional changes beyond this would
   require some intervention by the network operator.

   A description of the control plane aspects of this problem are
   discussed further in Section 5.4.  A description of the management
   plane aspects of this feature can be found in Section 5.5.

3.6.  Applicability to Overlay Technologies

   The concept of VPN+ can be applied to any existing and future multi-
   tenancy overlay technologies including but not limited to :

   *  Layer-2 point-to-point services such as pseudowires [RFC3985]

   *  Layer-2 VPNs [RFC4664]

   *  Ethernet VPNs [RFC7209], [RFC7432]

   *  Layer-3 VPNs [RFC4364], [RFC2764]

   Where such VPN service types need enhanced isolation and delivery
   characteristics, the technologies described in Section 5 can be used
   to tweak the underlay so that to provide the required enhanced

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3.7.  Inter-Domain and Inter-Layer Network

   In some scenarios, a VPN+ service may span multiple network domains.
   A domain is considered to be any collection of network elements under
   the responsibility of the same administrative entity, for example, an
   Autonomous System (AS).  In some domains the network operator may
   manage a multi-layered network, for example, a packet network over an
   optical network.  When VPN+ services are provisioned in such network
   scenarios, the technologies used in different network planes (data
   plane, control plane, and management plane) need to provide
   mechanisms to support multi-domain and multi-layer coordination and
   integration, so as to provide the required service characteristics
   for different VPN+ services, and improve network efficiency and
   operational simplicity.

4.  The Architecture of VPN+

   A number of VPN+ services will typically be provided by a common
   network infrastructure.  Each VPN+ service is provisioned with an
   overlay VPN and mapped to a corresponding VTN, which has a specific
   set of network resources and functions allocated in the underlay to
   satisfy the needs of the customer.  One VTN may support one of more
   VPN+ services.  The integration between the overlay connectivity and
   the underlay resources ensures the required isolation between
   different VPN+ services, and achieves the guaranteed performance for
   different customers.

   The VPN+ architecture needs to be designed with consideration given

   *  An enhanced data plane.

   *  A control plane to create VPN+, making use of the data plane
      isolation and performance guarantee techniques.

   *  A management plane for VPN+ service life-cycle management.

   These topics are expanded below.

   *  The enhanced data plane:

      -  Provides the required packet latency and jitter

      -  Provides the required packet loss characteristics.

      -  Provides the required resource isolation capability, e.g.,
         bandwidth guarantee.

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      -  Provides the mechanism to associate a packet with the set of
         resources allocated to a VTN which the VPN+ service packet is
         mapped to.

   *  The control plane:

      -  Collects information about the underlying network topology and
         network resources, and exports this to network nodes and/or a
         centralized controller as required.

      -  Creates VTNs with the network resource and topology properties
         needed by the VPN+ services.

      -  Distributes the attributes of VTNs to network nodes which
         participate in the VTNs and/or a centralized controller.

      -  Computes and set up network paths in each VTN.

      -  Maps VPN+ services to an appropriate VTN.

      -  Determines the risk of SLA violation and takes appropriate
         avoiding/correction actions.

      -  Considers the right balance of per-packet and per-node state
         according to the needs of the VPN+ services to scale to the
         required size.

   *  The management plane:

      -  Provides an interface between the VPN+ service provider (e.g.,
         operator's network management system) and the VPN+ customer
         (e.g., an organization or a service with VPN+ requirement) such
         that the operation requests and the related parameters can be
         exchanged without the awareness of other VPN+ customers.

      -  Provides an interface between the VPN+ service provider and the
         VPN+ customers to expose the network capability information
         toward the customer.

      -  Provides the service life-cycle management and operation of
         VPN+ services (e.g., creation, modification, assurance/
         monitoring, and decommissioning).

   *  Operations, Administration, and Maintenance (OAM):

      -  Provides the tools to verify the connectivity and monitor the
         performance of the VPN+ service.

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      -  Provides the tools to verify whether the underlay network
         resources are correctly allocated and operating properly.

   *  Telemetry:

      -  Provides the mechanisms to collect network information about
         the operation of the data plane, control plane, and management
         plane.  More specifically, telemetry provides the mechanisms to
         collect network data:

         o  from the underlay network for overall performance evaluation
            and for the planning VPN+ services.

         o  from each VPN+ service for monitoring and analytics of the
            characteristics and SLA fulfillment of the VPN+ services.

4.1.  Layered Architecture

   The layered architecture of VPN+ is shown in Figure 2.

   Underpinning everything is the physical network infrastructure layer
   which provide the underlying resources used to provision the
   separated VTNs.  This layer is responsible for the partitioning of
   link and/or node resources for different VTNs.  Each subset of link
   or node resource can be considered as a virtual link or virtual node
   used to build the VTNs.

                      +-------------------+       Centralized
                      | Network Controller|   Control & Management
                  o---------------------------o      VPN-1
                  o____________/______________o      VPN-2
                  o___/     \_________________o      VPN-3
                             ......                  ...
                  o-----------\ /-------------o
                  o____________X______________o      VPN-n

                    /       o----o-----o      /
                   /       /          /      /       VTN-1

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                  / o-----o-----o----o----o /
                    /       o----o            /
                   /       /    / \          /       VTN-2
                  / o-----o----o---o------o /
                           ......                     ...
                   /             o----o       /
                  /             /    /       /       VTN-m
                 /  o-----o----o----o-----o /

                   ++++   ++++   ++++
                   ++++   +++\\  ++++
                    ||     || \\  ||                Physical
                    ||     ||  \\ ||                Network
            ++++   ++++   ++++  \\+++   ++++     Infrastructure
            ++++   ++++   ++++   ++++   ++++

       o    Virtual Node     ++++
                             +--+  Physical Node with resource partition
       --   Virtual Link     +--+
       ==  Physical Link with resource partition

                Figure 2: The Layered Architecture of VPN+

   Various components and techniques discussed in Section 5 can be used
   to enable resource partitioning of the physical network
   infrastructure, such as FlexE, TSN, dedicated queues, etc.  These
   partitions may be physical or virtual so long as the SLA required by
   the higher layers is met.

   Based on the set of network resource partitions provided by the
   physical network infrastructure, multiple VTNs can be created, each
   with a set of dedicated or shared network resources allocated from
   the physical underlay network, and each can be associated with a
   customized logical network topology, so as to meet the requirements
   of different VPN+ services or different groups of VPN+ services.
   According to the associated logical network topology, each VTN needs
   to be instantiated on a set of network nodes and links which are

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   involved in the logical topology.  And on each node or link, each VTN
   is associated with a set of local resources which are allocated for
   the processing of traffic in the VTN.  The VTN provides the
   integration between the logical network topology and the required
   underlying network resources.

   According to the service requirements on connectivity, performance
   and isolation, etc., VPN services can be mapped to the appropriate
   VTNs in the network.  Different VPN services can be mapped to
   different VTNs, while it is also possible that multiple VPNs are
   mapped to the same VTN.  Thus the VTN is an essential scaling
   technique, as it has the potential of eliminating per-path state from
   the network.  In addition, when a group of VPN+ services are mapped
   to a single VTN, only the network state of the single VTN needs to be
   maintained in the network (see Section 4.4 for more information).

   The network controller is responsible for creating a VTN, instructing
   the involved network nodes to allocate network resources to the VTN,
   and provisioning the VPN services on the VTN.  A distributed control
   plane may be used for distributing the VTN resource and topology
   attributes among nodes in the VTN.

   The process used to create VTNs and to allocate network resources for
   use by the VTNs needs to take a holistic view of the needs of all of
   the service provider's customers and to partition the resources
   accordingly.  However, within a VTN these resources can, if required,
   be managed via a dynamic control plane.  This provides the required
   scalability and isolation with some flexibility.

4.2.  Multi-Point to Multi-Point (MP2MP) Connectivity

   At the VPN service level, the required connectivity for an MP2MP VPN
   service is usually full or partial mesh.  To support such VPN
   services, the corresponding VTN also needs to provide MP2MP
   connectivity among the end points.

   Other service requirements may be expressed at different
   granularities, some of which can be applicable to the whole service,
   while some others may only be applicable to some pairs of end points.
   For example, when a particular level of performance guarantee is
   required, the point-to-point path through the underlying VTN of the
   VPN+ service may need to be specifically engineered to meet the
   required performance guarantee.

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4.3.  Application Specific Data Types

   Although a lot of the traffic that will be carried over VPN+ will
   likely be IP based, the design must be capable of carrying other
   traffic types, in particular Ethernet traffic.  This is easily
   accomplished through the various pseudowire (PW) techniques
   [RFC3985].  Where the underlay is MPLS, Ethernet traffic can be
   carried over VPN+ encapsulated according to the method specified in
   [RFC4448].  Where the underlay is IP, Layer Two Tunneling Protocol -
   Version 3 (L2TPv3) [RFC3931] can be used with Ethernet traffic
   carried according to [RFC4719].  Encapsulations have been defined for
   most of the common layer-2 types for both PW over MPLS and for

4.4.  Scaling Considerations

   VPNs are instantiated as overlays on top of an operator's network and
   offered as services to the operator's customers.  An important
   feature of overlays is that they can deliver services without placing
   per-service state in the core of the underlay network.

   VPN+ may need to install some additional state within the network to
   achieve the features that they require.  Solutions must consider
   minimizing and controlling the scale of such state, and deployment
   architectures should constrain the number of VPN+ services so that
   the additional state introduced to the network is acceptable and
   under control.  It is expected that the number of VPN+ services will
   be small at the beginning, and even in the future the number of VPN+
   services will be fewer than traditional VPNs because existing VPN
   techniques are good enough to meet the needs of most existing VPN-
   type services.

   In general, it is not required that the state in the network be
   maintained in a 1:1 relationship with the VPN+ services.  It will
   usually be possible to aggregate a set or group of VPN+ services so
   that they share the same VTN and the same set of network resources
   (much in the same way that current VPNs are aggregated over transport
   tunnels) so that collections of VPN+ services that require the same
   behavior from the network in terms of resource reservation, latency
   bounds, resiliency, etc. can be grouped together.  This is an
   important feature to assist with the scaling characteristics of VPN+

   [I-D.ietf-teas-nrp-scalability] provides more details of scalability
   considerations for the network resource partitions used to
   instantiate VTNs, and Section 7 includes a greater discussion of
   scalability considerations.

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5.  Candidate Technologies

   A VPN is a virtual network created by applying a demultiplexing
   technique to the underlying network (the underlay) to distinguish the
   traffic of one VPN from that of another.  The connections of VPN are
   supported by a set of underlay paths.  A path that travels by other
   than the shortest path through the underlay normally requires state
   to specify that path.  The state of the paths could be applied to the
   underlay through the use of the RSVP-TE signaling protocol, or
   directly through the use of an SDN controller.  Based on Segment
   Routing, state could be maintained at the ingress node of the path,
   and carried in the data packet.  Other techniques may emerge as this
   problem is studied.  This state gets harder to manage as the number
   of paths increases.  Furthermore, as we increase the coupling between
   the underlay and the overlay to support the VPN+ service, this state
   is likely to increase further.  We cannot, for example, share the
   paths and network resource between VPN+ services which require hard

   VTN can be used to provide a group of virtual underlay paths (VTP)
   with a common set of network resources.  Through the use of VTNs, a
   subset of underlay network resource can be either dedicated for a
   particular VPN+ service or shared among a group of VPN+ services.
   This section describes the candidate technologies in different
   network planes which can be used to build VTNs.

5.1.  Forwarding Resource Partitioning

   Several candidate layer-2 packet- or frame-based forwarding plane
   mechanisms which can provide the required resource isolation and
   performance guarantees are described in the following sections.

5.1.1.  Flexible Ethernet

   FlexE [FLEXE] provides the ability to multiplex channels over an
   Ethernet link to create point-to-point fixed-bandwidth connections in
   a way that provides hard isolation.  FlexE also supports bonding
   links to create larger links out of multiple low capacity links.

   However, FlexE is only a link level technology.  When packets are
   received by the downstream node, they need to be processed in a way
   that preserves that isolation in the downstream node.  This in turn
   requires a queuing and forwarding implementation that preserves the
   end-to-end isolation.

   If different FlexE channels are used for different services, then no
   sharing is possible between the FlexE channels.  This means that it
   may be difficult to dynamically redistribute unused bandwidth to

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   lower priority services in another FlexE channel.  If one FlexE
   channel is used by one customer, the customer can use some methods to
   manage the relative priority of their own traffic in the FlexE

5.1.2.  Dedicated Queues

   DiffServ based queuing systems are described in [RFC2475] and
   [RFC4594].  This approach is not sufficient to provide isolation for
   VPN+ services because DiffServ does not provide enough markers to
   differentiate between traffic of a large number of VPN+ services.
   Nor does DiffServ offer the range of service classes that each VPN+
   service needs to provide to its tenants.  This problem is
   particularly acute with an MPLS underlay, because MPLS only provides
   eight traffic classes.

   In addition, DiffServ, as currently implemented, mainly provides per-
   hop priority-based scheduling, and it is difficult to use it to
   achieve quantitative resource reservation for different VPN+

   To address these problems and to reduce the potential interference
   between VPN+ services, it would be necessary to steer traffic to
   dedicated input and output queues per VPN+ service or per group of
   VPN+ services: some routers have a large number of queues and
   sophisticated queuing systems which could support this, while some
   routers may struggle to provide the granularity and level of
   isolation required by the applications of VPN+.

5.1.3.  Time Sensitive Networking

   Time Sensitive Networking (TSN) [TSN] is an IEEE project to provide a
   method of carrying time sensitive information over Ethernet.  It
   introduces the concept of packet scheduling where a packet stream may
   be given a time slot guaranteeing that it experiences no queuing
   delay or increase in latency beyond the very small scheduling delay.
   The mechanisms defined in TSN can be used to meet the requirements of
   time sensitive traffic flows of VPN+ service.

   Ethernet can be emulated over a layer-3 network using an IP or MPLS
   pseudowire.  However, a TSN Ethernet payload would be opaque to the
   underlay and thus not treated specifically as time sensitive data.
   The preferred method of carrying TSN over a layer-3 network is
   through the use of deterministic networking as explained in
   Section 5.2.1.

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5.2.  Data Plane Encapsulation and Forwarding

   This section considers the problem of VPN+ service differentiation
   and the representation of underlying network resources in the network
   layer.  More specifically, it describes the possible data plane
   mechanisms to determine the network resources and the logical network
   topology or paths associated with a VTN.

5.2.1.  Deterministic Networking

   Deterministic Networking (DetNet) [RFC8655] is a technique being
   developed in the IETF to enhance the ability of layer-3 networks to
   deliver packets more reliably and with greater control over the
   delay.  The design cannot use re-transmission techniques such as TCP
   since that can exceed the delay tolerated by the applications.
   DetNet pre-emptively sends copies of the packet over various paths to
   minimize the chance of all copies of a packet being lost.  It also
   seeks to set an upper bound on latency, but the goal is not to
   minimize latency.  Detnet can be realized over IP data plane
   [RFC8939] or MPLS data plane [RFC8964], and may be used to provide
   Virtual Transport Paths (VTPs) for VPN+ services.

5.2.2.  MPLS Traffic Engineering (MPLS-TE)

   MPLS-TE [RFC2702][RFC3209] introduces the concept of reserving end-
   to-end bandwidth for a TE-LSP, which can be used to provide a point-
   to-point Virtual Transport Path (VTP) across the underlay network to
   support VPN services.  VPN traffic can be carried over dedicated TE-
   LSPs to provide reserved bandwidth for each specific connection in a
   VPN, and VPNs with similar behavior requirements may be multiplexed
   onto the same TE-LSPs.  Some network operators have concerns about
   the scalability and management overhead of MPLS-TE system, especially
   with regard to those systems that use an active control plane, and
   this has lead them to consider other solutions for traffic
   engineering in their networks.

5.2.3.  Segment Routing

   Segment Routing (SR) [RFC8402] is a method that prepends instructions
   to packets at the head-end of a path.  These instructions are used to
   specify the nodes and links to be traversed, and allow the packets to
   be routed on paths other than the shortest path.  By encoding the
   state in the packet, per-path state is transitioned out of the
   network.  SR can be instantiated using MPLS data plane (SR-MPLS) or
   IPv6 data plane (SRv6).

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   An SR traffic engineered path operates with a granularity of a link.
   Hints about priority are provided using the Traffic Class (TC) field
   in the packet header.  However, to achieve the performance and
   isolation characteristics that are sought by VPN+ customers, it will
   be necessary to steer packets through specific virtual links and/or
   queues on the same link and direct them to use specific resources.
   With SR, it is possible to introduce such fine-grained packet
   steering by specifying the queues and the associated resources
   through an SR instruction list.

   Note that the concept of a queue is a useful abstraction for
   different types of underlay mechanism that may be used to provide
   enhanced isolation and performance support.  How the queue satisfies
   the requirement is implementation specific and is transparent to the
   layer-3 data plane and control plane mechanisms used.

   With Segment Routing, the SR instruction list could be used to build
   a P2P path, and a group of SR SIDs could also be used to represent an
   MP2MP network.  Thus, the SR based mechanism could be used to provide
   both a Virtual Transport Path (VTP) and a Virtual Transport Network
   (VTN) for VPN+ services.

5.3.  Non-Packet Data Plane

   Non-packet underlay data plane technologies often have TE properties
   and behaviors, and meet many of the key requirements in particular
   for bandwidth guarantees, traffic isolation (with physical isolation
   often being an integral part of the technology), highly predictable
   latency and jitter characteristics, measurable loss characteristics,
   and ease of identification of flows.  The cost is that the resources
   are allocated on a long-term and end-to-end basis.  Such an
   arrangement means that the full cost of the resources has to be borne
   by the client that is allocated with the resources.  When a VTN built
   with this data plane can be used to support multiple VPN+ services,
   the cost could be distributed among such group of services.

5.4.  Control Plane

   The control plane of VPN+ would likely be based on a hybrid control
   mechanism that takes advantage of a logically centralized controller
   for on-demand provisioning and global optimization, whilst still
   relying on a distributed control plane to provide scalability, high
   reliability, fast reaction, automatic failure recovery, etc.
   Extension to and optimization of the centralized and distributed
   control plane is needed to support the enhanced properties of VPN+.

   As described in section 4, the VPN+ control plane needs to provide
   the following functions:

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   *  Collect information about the underlying network topology and
      network resources, and exports this to network nodes and/or a
      centralized controller as required.

   *  Create VTNs with the network resource and topology properties
      needed by the VPN+ services.

   *  Distribute the attributes of VTNs to network nodes which
      participate in the VTNs and/or the centralized controller.

   *  Map VPN+ services to an appropriate VTN.

   *  Compute and set up VTPs in each VTN to meet VPN+ service

   The collection of underlying network topology and resource
   information can be done using existing the IGP and BGP-LS based
   mechanisms.  The creation of VTN and the distribution of VTN
   attributes may need further control protocol extensions.  The
   computation of VTPs based on the attributes and constraints of the
   VTN can be performed either by the headend node of the path or a
   centralized Path Computation Element (PCE).

   There are two candidate mechanisms for the setup of VTPs in the VTN:
   RSVP-TE and Segment Routing (SR).

   *  RSVP-TE [RFC3209] provides the signaling mechanism for
      establishing a TE-LSP in an MPLS network with end-to-end resource
      reservation.  This can be seen as an approach of providing a
      Virtual Transport Path (VTP) which could be used to bind the VPN
      to specific network resources allocated within the underlay, but
      there remain scalability concerns as mentioned in Section 5.2.2.

   *  The SR control plane [RFC8665] [RFC8667] [RFC9085] does not have
      the capability of signaling resource reservations along the path.
      On the other hand, the SR approach provides a potential way of
      binding the underlay network resource and the VTNs without
      requiring per-path state to be maintained in the network.  A
      centralized controller can perform resource planning and
      reservation for VTNs, and it needs to instruct the network nodes
      to ensure that resources are correctly allocated for the VTN.  The
      controller could provision the SR paths based on the mechanism in
      [RFC9256] to the headend nodes of the paths.

   According to the service requirements for connectivity, performance
   and isolation, one VPN+ service may be mapped a dedicated VTN, or a
   group of VPN+ services may be mapped to the same VTN.  The mapping of
   VPN+ services to VTN can be achieved using existing control

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   mechanisms with possible extensions, and it can be based on either
   the characteristics of the data packet or the attributes of the VPN
   service routes.

5.5.  Management Plane

   The management plane provides the interface between the VPN+ service
   provider and the customers for life-cycle management of the VPN+
   service (i.e., creation, modification, assurance/monitoring, and
   decommissioning).  It relies on a set of service data models for the
   description of the information and operations needed on the

   As an example, in the context of 5G end-to-end network slicing
   [TS28530], the management of the transport network segment of the 5G
   end-to-end network slice can be realized with the management plane of
   VPN+. The 3GPP management system may provide the connectivity and
   performance related parameters as requirements to the management
   plane of the transport network.  It may also require the transport
   network to expose the capabilities and status of the network slice.
   Thus, an interface between the VPN+ management plane and the 5G
   network slice management system, and relevant service data models are
   needed for the coordination of 5G end-to-end network slice

   The management plane interface and data models for VPN+ services can
   be based on the service models described in Section 5.6.

   It is important that the management life-cycle supports in-place
   modification of VPN+ services.  That is, it should be possible to add
   and remove end points, as well as to change the requested
   characteristics of the service that is delivered.  The management
   system needs to be able to assess the revised VPN+ requests and
   determine whether they can be provided by the existing VTNs or
   whether changes must be made, and it will additionally need to
   determine whether those changes to the VTN are possible.  If not,
   then the customer's modification request may be rejected.

   When the modification of a VPN+ service is possible, the management
   system must make every effort to make the changes in a non-disruptive
   way.  That is, the modification of the VPN+ service or the underlying
   VTN must not perturbate traffic on the VPN+ service in a way that
   causes the service level to drop below the agreed levels.
   Furthermore, in the spirit of isolation, changes to one VPN+ service
   should not cause disruption to other VPN+ services.

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   The network operator for the underlay network (i.e., the provider of
   the VPN+ service) may delegate some operational aspects of the
   overlay VPN and the underlying VTN to the customer.  In this way, the
   VPN+ is presented to the customer as a virtual network, and the
   customer can choose how to use that network.  Some mechanisms in the
   operator's network is needed, so that a customer cannot exceed the
   capabilities of the virtual links and nodes, but can decide how to
   load traffic onto the network, for example, by assigning different
   metrics to the virtual links so that the customer can control how
   traffic is routed through the virtual network.  This approach
   requires a management system for the virtual network, but does not
   necessarily require any coordination between the management systems
   of the virtual network and the physical network, except that the
   virtual network management system might notice when the VTN is close
   to capacity or considerably under-used and automatically request
   changes in the service provided by the underlay network.

5.6.  Applicability of Service Data Models to VPN+

   This section describes the applicability of the existing and in-
   progress service data models to VPN+. [RFC8309] describes the scope
   and purpose of service models and shows where a service model might
   fit into an SDN based network management architecture.  New service
   models may also be introduced for some of the required management

   Service data models are used to represent, monitor, and manage the
   virtual networks and services enabled by VPN+. The VPN customer
   service models (e.g., the Layer-3 VPN Service Model (L3SM) [RFC8299],
   the Layer-2 VPN Service Model (L2SM) [RFC8466]), or the ACTN Virtual
   Network (VN) model [I-D.ietf-teas-actn-vn-yang]) are service models
   which can provide the customer's view of the VPN+ service.  The
   Layer-3 VPN Network Model (L3NM) [RFC9182], the Layer-2 VPN network
   model (L2NM) [I-D.ietf-opsawg-l2nm] provide the operator's view of
   the managed infrastructure as a set of virtual networks and the
   associated resources.  The NRP model [I-D.wd-teas-nrp-yang] further
   provides the management of the virtual underlay network topology and
   resources both in the controller and in the network devices to
   instantiate the VTNs needed for the VPN+ services.

6.  Applicability in Network Slice Realization

   One of the typical use cases of VPN+ is to deliver IETF Network Slice
   Service.  This section describes the applicability of VPN+ in network
   slice realization.

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   In order to provide IETF network slices to customers, a technology-
   agnostic network slice service model
   [I-D.ietf-teas-ietf-network-slice-nbi-yang] is needed for the
   customers to communicate the requirements of IETF network slices (end
   points, connectivity, SLOs, and SLEs).  These requirements may be
   realized using technology specified in this document to instruct the
   network to instantiate a VPN+ service to meet the requirements of the
   IETF network slice customers.

6.1.  VTN Planning

   According to the network operators' network resource planning policy,
   or based on the requirement of one or a group of customers or
   services, a VTN may need to be created to support the requested VPN+
   services.  One of the basic requirements for a VTN is to provide a
   set of dedicated network resources to avoid unexpected interference
   from other services in the same network.  Other possible requirements
   may include the required topology and connectivity, bandwidth,
   latency, reliability, etc.

   A centralized network controller can be responsible for calculating a
   subset of the underlay network topology (which is called a logical
   topology) to support the VTN requirement.  And on the network nodes
   and links within the logical topology, the set of network resources
   to be allocated to the VTN can also be determined by the controller.
   Normally such calculation needs to take the underlay network
   connectivity information and the available network resource
   information of the underlay network into consideration.  The network
   controller may also take the status of the existing VTNs into
   consideration in the planning and calculation of a new VTN.

6.2.  VTN Instantiation

   According to the result of the VTN planning, the network nodes and
   links involved in the logical topology of the VTN are instructed to
   allocated the required set of network resources for the VTN.  One or
   multiple mechanisms as specified in section 5.1 can be used to
   partition the forwarding plane network resources and allocate
   different subsets of resources to different VTNs.  In addition, the
   data plane identifiers which are used to identify the set of network
   resources allocated to the VTN are also provisioned on the network
   nodes.  Depends on the data plane technologies used, the set of
   network resources of a VTN can be identified using either resource
   aware SR segments as specified in
   [I-D.ietf-spring-resource-aware-segments], or a dedicated VTN
   resource ID as specified in [I-D.ietf-6man-enhanced-vpn-vtn-id] can
   be introduced.  The network nodes involved in a VTN may distribute
   the logical topology information, the VTN specific network resource

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   information and the VTN resource identifiers using the control plane.
   Such information could be used by the controller and the network
   nodes to compute the TE or shortest paths within the VTN, and install
   the VTN specific forwarding entries to network nodes.

6.3.  VPN+ Service Provisioning

   According to the connectivity requirements of an IETF network slice
   service, an overlay VPN can be created using the existing or future
   multi-tenancy overlay technologies as described in Section 3.6.

   Then according to the SLO and SLE requirements of the network slice,
   the overlay VPN is mapped to an appropriate VTN as the virtual
   underlay.  The integration of the overlay VPN and the underlay VTN
   together provide a VPN+ service which can meet the network slice
   service requirements.

6.4.  Network Slice Traffic Steering and Forwarding

   At the edge of the operator's network, traffic of IETF network slices
   can be classified based on the rules defined by the operator's
   policy, so that the traffic is treated as a specific VPN+ service,
   which is further mapped to a underlay VTN.  Packets belonging to the
   VPN+ service will be processed and forwarded by network nodes based
   the TE or shortest path forwarding entries and the set of network
   resources of the corresponding VTN.

7.  Scalability Considerations

   VPN+ provides performance guaranteed services in packet networks, but
   with the potential cost of introducing additional state into the
   network.  There are at least three ways that this additional state
   might be brought into the network:

   *  Introduce the complete state into the packet, as is done in SR.
      This allows the controller to specify the detailed series of
      forwarding and processing instructions for the packet as it
      transits the network.  The cost of this is an increase in the
      packet header size.  The cost is also that systems will have
      capabilities enabled in case they are called upon by a service.
      This is a type of latent state, and increases as the path and
      resources that need to be exclusively available to a VPN are
      specified more precisely.

   *  Introduce the state to the network.  This is normally done by
      creating a path using signaling such as RSVP-TE.  This could be
      extended to include any element that needs to be specified along
      the path, for example explicitly specifying queuing policy.  It is

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      also possible to use other methods to introduce path state, such
      as via an SDN controller, or possibly by modifying a routing
      protocol.  With this approach there is state per path: per-path
      characteristic that needs to be maintained over the life of the
      path.  This is more network state than is needed using SR, but the
      packets are usually shorter.

   *  Provide a hybrid approach.  One example is based on using binding
      SIDs [RFC8402] to represent path fragments, and bind them together
      with SR.  Dynamic creation of a VPN service path using SR requires
      less state maintenance in the network core at the expense of
      larger packet headers.  The packet size can be lower if a form of
      loose source routing is used (using a few nodal SIDs), and it will
      be lower if no specific functions or resources on the routers are

   Reducing the state in the network is important to VPN+, as it
   requires the overlay to be more closely integrated with the underlay
   than with traditional VPNs.  This tighter coupling would normally
   mean that more state needs to be created and maintained in the
   network, as the state about fine granularity processing would need to
   be loaded and maintained in the routers.  Aggregation is a well-
   established approach to reduce the amount of state and improve
   scaling, and VTN is considered as the network construct to aggregate
   the states of VPN+ services.  In addition, an SR approach allows much
   of the state to be spread amongst the network ingress nodes, and
   transiently carried in the packets as SIDs.

   The following sections describe some of the scalability concerns that
   need to be considered.  Further discussion of the scalability
   considerations of the underlaying network construct of VPN+ can be
   found in [I-D.ietf-teas-nrp-scalability].

7.1.  Maximum Stack Depth of SR

   One of the challenges with SR is the stack depth that nodes are able
   to impose on packets [RFC8491].  This leads to a difficult balance
   between adding state to the network and minimizing stack depth, or
   minimizing state and increasing the stack depth.

7.2.  RSVP-TE Scalability

   The established method of creating a resource allocated path through
   an MPLS network is to use the RSVP-TE protocol.  However, there have
   been concerns that this requires significant continuous state
   maintenance in the network.  Work to improve the scalability of RSVP-
   TE LSPs in the control plane can be found in [RFC8370].

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   There is also concern at the scalability of the forwarder footprint
   of RSVP-TE as the number of paths through a label switching router
   (LSR) grows.  [RFC8577] addresses this by employing SR within a
   tunnel established by RSVP-TE.

7.3.  SDN Scaling

   The centralized approach of SDN requires state to be stored in the
   network, but does not have the overhead of also requiring control
   plane state to be maintained.  Each individual network node may need
   to maintain a communication channel with the SDN controller, but that
   compares favorably with the need for a control plane to maintain
   communication with all neighbors.

   However, SDN may transfer some of the scalability concerns from the
   network to the centralized controller.  In particular, there may be a
   heavy processing burden at the controller, and a heavy load in the
   network surrounding the controller.  A centralized controller also
   presents a single point of failure within the network.

8.  Manageability Considerations

   Operations, Administration, and Maintenance (OAM) are necessary
   functionalities for network and service management.  The OAM
   mechanisms can be further classified as OAM and telemetry.  This
   section describes the considerations of both classes of OAM

8.1.  OAM Considerations

   The design of OAM for VPN+ services needs to consider the following

   *  Instrumentation of the underlay so that the network operator can
      be sure that the resources committed to a customer are operating
      correctly and delivering the required performance.

   *  Instrumentation of the overlay by the customer.  This is likely to
      be transparent to the network operator and to use existing
      methods.  Particular consideration needs to be given to the need
      to verify the isolation and the various committed performance

   *  Instrumentation of the overlay by the network provider to
      proactively demonstrate that the committed performance is being
      delivered.  This needs to be done in a non-intrusive manner,
      particularly when the tenant is deploying a performance sensitive

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   *  Verification of the conformity of the path to the service
      requirement.  This may need to be done as part of a commissioning

   A study of OAM in SR networks has been documented in [RFC8403].

8.2.  Telemetry Considerations

   Network visibility is essential for network operation.  Network
   telemetry has been considered as an ideal means to gain sufficient
   network visibility with better flexibility, scalability, accuracy,
   coverage, and performance than conventional OAM technologies.

   As defined in [RFC9232], the objective of Network Telemetry is to
   acquire network data remotely for network monitoring and operation.
   It is a general term for a large set of network visibility techniques
   and protocols.  Network telemetry addresses the current network
   operation issues and enables smooth evolution toward intent-driven
   autonomous networks.  Telemetry can be applied on the forwarding
   plane, the control plane, and the management plane in a network.

   How the telemetry mechanisms could be used or extended for the VPN+
   service is out of the scope of this document.

9.  Enhanced Resiliency

   Each VPN+ service has a life cycle, and may need modification during
   deployment as the needs of its tenant change.  This is discussed in
   Section 5.5.  Additionally, as the network evolves, there may need to
   be garbage collection performed to consolidate resources into usable

   Systems in which the path is imposed, such as SR or some form of
   explicit routing, tend to do well in these applications, because it
   is possible to perform an atomic transition from one path to another.
   That is, a single action by the head-end that changes the path
   without the need for coordinated action by the routers along the
   path.  However, implementations and the monitoring protocols need to
   make sure that the new path is operational and meets the required SLA
   before traffic is transitioned to it.  It is possible for deadlocks
   to arise as a result of the network becoming fragmented over time,
   such that it is impossible to create a new path or to modify an
   existing path without impacting the SLA of other paths.  Resolution
   of this situation is as much a commercial issue as it is a technical
   issue and is outside the scope of this document.

   There are, however, two manifestations of the latency problem that
   are for further study in any of these approaches:

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   *  The problem of packets overtaking one another if a path latency
      reduces during a transition.

   *  The problem of transient variation in latency in either direction
      as a path migrates.

   There is also the matter of what happens during failure in the
   underlay infrastructure.  Fast reroute is one approach, but that
   still produces a transient loss with a normal goal of rectifying this
   within 50ms [RFC5654].  An alternative is some form of N+1 delivery
   such as has been used for many years to support protection from
   service disruption.  This may be taken to a different level using the
   techniques of DetNet with multiple in-network replication and the
   culling of later packets [RFC8655].

   In addition to the approach used to protect high priority packets,
   consideration should be given to the impact of best effort traffic on
   the high priority packets during a transition.  Specifically, if a
   conventional re-convergence process is used there will inevitably be
   micro-loops and whilst some form of explicit routing will protect the
   high priority traffic, lower priority traffic on best effort shortest
   paths will micro-loop without the use of a loop prevention
   technology.  To provide the highest quality of service to high
   priority traffic, either this traffic must be shielded from the
   micro-loops, or micro-loops must be prevented completely.

10.  Operational Considerations

   It is likely that VPN+ services will be introduced in networks which
   already have VPN services deployed.  Depending on service
   requirements, the tenants or the operator may choose to use a VPN or
   a VPN+ to fulfill a service requirement.  The information and
   parameters to assist such a decision needs to be reflected on the
   management interface between the tenant and the operator.

11.  Security Considerations

   All types of virtual network require special consideration to be
   given to the isolation of traffic belonging to different tenants.
   That is, traffic belonging to one VPN must not be delivered to end
   points outside that VPN.  In this regard VPN+ neither introduce, nor
   experience greater security risks than other VPNs.

   However, in a VPN+ service the additional service requirements need
   to be considered.  For example, if a service requires a specific
   upper bound to latency then it can be damaged by simply delaying the
   packets through the activities of another tenant, i.e., by
   introducing bursts of traffic for other services.  In some respects

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   this makes the VPN+ more susceptible to attacks since the SLA may be
   broken.  But another view is that the operator must, in any case,
   preform monitoring of the VPN+ to ensure that the SLA is met, and
   this means that the operator may be more likely to spot the early
   onset of a security attack and be able to take pre-emptive protective

   The measures to address these dynamic security risks must be
   specified as part to the specific solution are form part of the
   isolation requirements of a service.

   While a VPN+ service may be sold as offering encryption and other
   security features as part of the service, customers would be well
   advised to take responsibility for their own security requirements
   themselves possibly by encrypting traffic before handing it off to
   the service provider.

   The privacy of VPN+ service customers must be preserved.  It should
   not be possible for one customer to discover the existence of another
   customer, nor should the sites that are members of an VPN+ be
   externally visible.

   A VPN+ service (even one with hard isolation requirements) does not
   provide any additional guarantees of privacy for customer traffic
   compared to regular VPNs: the traffic within the network may be
   intercepted and errors may lead to mis-delivery.  Users who wish to
   ensure the privacy of their traffic must take their own precautions
   including end-to-end encryption.

12.  IANA Considerations

   There are no requested IANA actions.

13.  Contributors

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      Daniel King

      Adrian Farrel

      Jeff Tansura

      Zhenbin Li

      Qin Wu

      Bo Wu

      Daniele Ceccarelli

      Mohamed Boucadair

      Sergio Belotti

      Haomian Zheng

14.  Acknowledgements

   The authors would like to thank Charlie Perkins, James N Guichard,
   John E Drake, Shunsuke Homma, and Luis M.  Contreras for their review
   and valuable comments.

   This work was supported in part by the European Commission funded
   H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727).

15.  References

15.1.  Normative References

   [RFC2764]  Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
              Malis, "A Framework for IP Based Virtual Private
              Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,

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   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,

15.2.  Informative References

   [DETNET]   "Deterministic Networking", March ,

   [FLEXE]    "Flex Ethernet Implementation Agreement", March 2016,

              Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra,
              "Carrying Virtual Transport Network (VTN) Information in
              IPv6 Extension Header", Work in Progress, Internet-Draft,
              draft-ietf-6man-enhanced-vpn-vtn-id-01, 11 July 2022,

              Boucadair, M., Dios, O. G. D., Barguil, S., and L. A.
              Munoz, "A YANG Network Data Model for Layer 2 VPNs", Work
              in Progress, Internet-Draft, draft-ietf-opsawg-l2nm-19, 2
              June 2022, <

              Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
              Z., and F. Clad, "Introducing Resource Awareness to SR
              Segments", Work in Progress, Internet-Draft, draft-ietf-
              spring-resource-aware-segments-05, 8 September 2022,

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              Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B. Y.
              Yoon, "A YANG Data Model for Virtual Network (VN)
              Operations", Work in Progress, Internet-Draft, draft-ietf-
              teas-actn-vn-yang-15, 11 July 2022,

              King, D., Drake, J., Zheng, H., and A. Farrel,
              "Applicability of Abstraction and Control of Traffic
              Engineered Networks (ACTN) to Network Slicing", Work in
              Progress, Internet-Draft, draft-ietf-teas-applicability-
              actn-slicing-02, 6 September 2022,

              Wu, B., Dhody, D., Rokui, R., Saad, T., and L. Han, "IETF
              Network Slice Service YANG Model", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slice-nbi-
              yang-02, 11 July 2022, <

              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "Framework for IETF
              Network Slices", Work in Progress, Internet-Draft, draft-
              ietf-teas-ietf-network-slices-14, 3 August 2022,

              Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N.,
              Mishra, G., Qin, F., Saad, T., and V. P. Beeram,
              "Scalability Considerations for Network Resource
              Partition", Work in Progress, Internet-Draft, draft-ietf-
              teas-nrp-scalability-00, 11 July 2022,

              Wu, B., Dhody, D., and Y. Cheng, "A YANG Data Model for
              Network Resource Partition (NRP)", Work in Progress,
              Internet-Draft, draft-wd-teas-nrp-yang-01, 11 July 2022,

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              hao ,, "NGMN NS Concept", 2016,

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,

   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, DOI 10.17487/RFC2702, September 1999,

   [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,

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758,
              DOI 10.17487/RFC3758, May 2004,

   [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,

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <>.

   [RFC4448]  Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
              "Encapsulation Methods for Transport of Ethernet over MPLS
              Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              DOI 10.17487/RFC4594, August 2006,

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   [RFC4719]  Aggarwal, R., Ed., Townsley, M., Ed., and M. Dos Santos,
              Ed., "Transport of Ethernet Frames over Layer 2 Tunneling
              Protocol Version 3 (L2TPv3)", RFC 4719,
              DOI 10.17487/RFC4719, November 2006,

   [RFC5151]  Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
              Domain MPLS and GMPLS Traffic Engineering -- Resource
              Reservation Protocol-Traffic Engineering (RSVP-TE)
              Extensions", RFC 5151, DOI 10.17487/RFC5151, February
              2008, <>.

   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,

   [RFC7209]  Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
              Henderickx, W., and A. Isaac, "Requirements for Ethernet
              VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,

   [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
              Connectivity Provisioning Profile (CPP)", RFC 7297,
              DOI 10.17487/RFC7297, July 2014,

   [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, <>.

   [RFC7926]  Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
              Ceccarelli, D., and X. Zhang, "Problem Statement and
              Architecture for Information Exchange between
              Interconnected Traffic-Engineered Networks", BCP 206,
              RFC 7926, DOI 10.17487/RFC7926, July 2016,

   [RFC8172]  Morton, A., "Considerations for Benchmarking Virtual
              Network Functions and Their Infrastructure", RFC 8172,
              DOI 10.17487/RFC8172, July 2017,

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   [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,

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,

   [RFC8370]  Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and
              T. Saad, "Techniques to Improve the Scalability of RSVP-TE
              Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018,

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <>.

   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <>.

   [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,

   [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, <>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,

   [RFC8568]  Bernardos, CJ., Rahman, A., Zuniga, JC., Contreras, LM.,
              Aranda, P., and P. Lynch, "Network Virtualization Research
              Challenges", RFC 8568, DOI 10.17487/RFC8568, April 2019,

   [RFC8577]  Sitaraman, H., Beeram, V., Parikh, T., and T. Saad,
              "Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding
              Plane", RFC 8577, DOI 10.17487/RFC8577, April 2019,

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Internet-Draft               VPN+ Framework               September 2022

   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
              RFC 8578, DOI 10.17487/RFC8578, May 2019,

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,

   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,

   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
              S., and J. Korhonen, "Deterministic Networking (DetNet)
              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
              2021, <>.

   [RFC9085]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
              H., and M. Chen, "Border Gateway Protocol - Link State
              (BGP-LS) Extensions for Segment Routing", RFC 9085,
              DOI 10.17487/RFC9085, August 2021,

   [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, <>.

   [RFC9232]  Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
              A. Wang, "Network Telemetry Framework", RFC 9232,
              DOI 10.17487/RFC9232, May 2022,

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Internet-Draft               VPN+ Framework               September 2022

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,

   [SFC]      "Service Function Chaining", March ,

   [TS23501]  "3GPP TS23.501", 2016,

   [TS28530]  "3GPP TS28.530", 2016,

   [TSN]      "Time-Sensitive Networking", March ,

Authors' Addresses

   Jie Dong

   Stewart Bryant
   University of Surrey

   Zhenqiang Li
   China Mobile

   Takuya Miyasaka
   KDDI Corporation

   Young Lee

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