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Versions: 00 01

TEAS Working Group                                                 Z. Li
Internet-Draft                                                  D. Dhody
Intended status: Informational                                   H. Chen
Expires: September 2, 2018                           Huawei Technologies
                                                           March 1, 2018


                   Hierarchy of IP Controllers (HIC)
               draft-li-teas-hierarchy-ip-controllers-00

Abstract

   This document describes the interactions between various IP
   controllers in a hierarchical fashion to provide various IP services.
   It describes how the Abstraction and Control of Traffic Engineered
   Networks (ACTN) framework is applied to the Hierarchy of IP
   controllers (HIC) as well as document the interactions with other
   protocols like BGP, Path Computation Element Communication Protocol
   (PCEP) to provide end to end dynamic services spanning multiple
   domains and controllers (e.g.  Layer 3 Virtual Private Network
   (L3VPN), Seamless MPLS etc).

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 2, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Mapping to ACTN . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Interface between Super Controller and Domain Controller
           in HIC  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Key Concepts  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Topology  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Path Computation/Path instantiation . . . . . . . . . . .   7
     3.3.  BGP considerations  . . . . . . . . . . . . . . . . . . .   8
   4.  VPN Service . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Seamless MPLS . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  L3VPN . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     4.3.  L2VPN and EVPN service  . . . . . . . . . . . . . . . . .  11
   5.  Possible Features/Extensions  . . . . . . . . . . . . . . . .  11
   6.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Control Plane . . . . . . . . . . . . . . . . . . . . . .  12
       6.1.1.  PCE / PCEP  . . . . . . . . . . . . . . . . . . . . .  12
       6.1.2.  BGP . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  Management Plane  . . . . . . . . . . . . . . . . . . . .  13
       6.2.1.  YANG Models . . . . . . . . . . . . . . . . . . . . .  13
       6.2.2.  Protocol Considerations . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Software-Defined Networking (SDN) refers to a separation between the
   control elements and the forwarding components so that software
   running in a centralized system called a controller, can act to
   program the devices in the network to behave in specific ways.  A
   required element in an SDN architecture is a component that plans how
   the network resources will be used and how the devices will be
   programmed.  It is possible to view this component as performing
   specific computations to place flows within the network given
   knowledge of the availability of network resources, how other



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   forwarding devices are programmed, and the way that other flows are
   routed.  The Application-Based Network Operation (ABNO) [RFC7491]
   describes how various components and technologies fit together.

   A domain [RFC4655] is any collection of network elements within a
   common sphere of address management or path computation
   responsibility.  Specifically within this document we mean a part of
   an operator's network that is under common management.  Network
   elements will often be grouped into domains based on technology
   types, vendor profiles, and geographic proximity and under a domain
   controller.

   Multiple such domains in the network are interconnected, and a path
   is established through a series of connected domains to form an end-
   to-end path over which various services are offered.  Each domain is
   under the control of the domain controller (or lower-level
   controller), and a "super controller" (or high-level controller)
   takes responsibility for a high-level view of the network before
   distributing tasks to domain controllers (or lower-level
   controllers).  It is possible for each of the domain to use a
   different tunneling mechanism (eg RSVP-TE, Segment Routing (SR) etc).

   [I-D.ietf-teas-actn-framework] describes the framework for
   Abstraction and Control of Traffic Engineered Networks (ACTN) as well
   as a set of management and control functions used to operate multiple
   TE networks.  This documents would apply the ACTN principles to
   Hierarchy of IP controllers (HIC) and focus on the applicability and
   interactions with other protocol and technologies (specific to IP
   packet domains).

   Sometimes, service (such as Layer 3 Virtual Private Network (L3VPN),
   Layer 2 Virtual Private Network (L2VPN), Ethernet VPN (EVPN),
   Seamless MPLS) require sites attached to different domains (under the
   control of different domain controller) to be interconnected as part
   of the VPN service.  This require multi-domain coordination between
   domain controllers to compute and setup E2E path for the VPN service.

   This document describes the interactions between various IP
   controllers in a hierarchical fashion to provide various IP services.
   It describes how the Abstraction and Control of Traffic Engineered
   Networks (ACTN) framework is applied to the Hierarchy of IP
   controllers (HIC) as well as document the interactions with control
   plane protocols (like BGP, Path Computation Element Communication
   Protocol (PCEP)) and management plane aspects (Yang models) to
   provide end to end dynamic services spanning multiple domains and
   controllers (e.g.  L3VPN, Seamless MPLS etc).





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2.  Overview

   Figure 1 show examples of multi-domain IP domains under hierarchy of
   IP controllers.


                             |
                       +------------+
                       |  SuperCo   |
                       +------------+
                             |
             ----------------------------------
             |               |                |
      +------------+   +------------+   +------------+
      |   DoCo#1   |   |   DoCo#2   |   |   DoCo#3   |
      +------------+   +------------+   +------------+


      +--Domain#1--+   +--Domain#2--+   +--Domain#3--+
      |            |   |            |   |            |
      |     B------+---+---D-----E--+---+------J     |
      |    /       |   |    \   /   |   |       \    |
      |   /        |   |     \ /    |   |        \   |
      |  A         |   |      H     |   |         L  |
      |   \        |   |     / \    |   |        /   |
      |    \       |   |    /   \   |   |       /    |
      |     C------+---+---F-----G--+---+------K     |
      |            |   |            |   |            |
      +------------+   +------------+   +------------+


           Figure 1: Example: Hierarchy of IP controllers (HIC)

   The IP "Super Controller" receives request from the network/service
   orchestrator to setup dynamic services spanning multiple domains.
   The IP "Super Controller" breaks down and assigns tasks to the domain
   controllers, responsible for communicating to network devices in the
   domain.  It further coordinates between the controller to provide a
   unified view of the multi-domain network.

2.1.  Mapping to ACTN

   As per [I-D.ietf-teas-actn-framework], ACTN has following main
   functions -

   o  Multi-domain coordination

   o  Virtualization/Abstraction



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   o  Customer mapping/translation

   o  Virtual service coordination

   These functions are part of Multi Domain Service Coordinator (MDSC)
   and/or Provisioning Network Controller (PNC).  Further these
   functions are part of the controller / orchestrator.

   The HIC is an instantiation of ACTN framework for IP packet network.
   The IP domain (lower-level) controllers implements the PNC
   functionalities for configuring, controlling and monitoring the IP
   domain.  The "super controller" (high-level controller) implements
   the MDSC functionalities for coordination between multiple domains as
   well as maintaining an abstracted view of multiple domains.  It also
   takes care of the service related functionalities of customer
   mapping/translation and virtual service coordination.

   The ACTN functions are part of the IP controllers and responsible for
   the TE topology and E2E path computation/setup.  There are other
   functions along with ACTN that are needed to manage multiple IP
   domain networks.

2.2.  Interface between Super Controller and Domain Controller in HIC

   The interaction between super controller and domain controller in HIC
   is a combination of Control Plane and Management Plane interface as
   shown in Figure 2.  BGP [RFC4271] and PCEP [RFC5440] are example of
   the control plane interface; where as NETCONF [RFC6241] and RESTCONF
   [RFC8040] are example of management plane interface.






















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      +----------------------------------------------+
      |                Super Controller              |
      |                                              |
      |                                              |
      +------------------*------#---------------------+
                         *      #
                         *      #
                      *************************
                      *         #             *
                ######*###############        *
                #     *              #        *
      +---------#-----*--+        +--#--------*------+
      | Domain           |        | Domain           |
      | Controller       |        | Controller       |
      +--#------------*--+        +--#------------*--+
         #            *              #            *
         #            *              #            *


       * -> Control Plane Interface
       # -> Management Plane Interface



    Figure 2: Interface between Super Controller and Domain Controller

   Note that ACTN's MDSC-PNC Interface (MPI) could be implemented via
   management plane interface using Yang models
   [I-D.ietf-teas-actn-yang] or via PCEP control plane interface
   [I-D.ietf-pce-applicability-actn].

3.  Key Concepts

3.1.  Topology

   The Domain Controller is expected to be aware of the topology of the
   network devices in its domain.  The domain controller could
   participate in the IGP ([RFC3630] and [RFC5305]) or use BGP-LS
   [RFC7752] by which link-state and TE information is collected and
   shared with domain controller using the BGP routing protocol.

   An alternate approach would be to rely on the management plane
   interface which uses the YANG model for network/TE Topology as per
   [I-D.ietf-i2rs-yang-network-topo] and [I-D.ietf-teas-yang-te-topo].

   The domain controller is expected to share the domain topology to the
   Super Controller as aligned to ACTN (where PNC abstract the topology
   towards MDSC).  A level of abstraction is usually applied while



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   presenting the topology to a higher level controller.  Topology
   abstraction is described in [RFC7926] as well as
   [I-D.ietf-teas-actn-framework].  BGP-LS, PCEP-LS
   [I-D.dhodylee-pce-pcep-ls] or management plane interface based on the
   abstracted network/TE Topology could be used to carry the abstract
   topology to the super-controller.  At minimum the border nodes and
   inter-domain links are exposed to the super-controller.

   Further [I-D.ietf-teas-actn-framework] defines three types of
   topology abstraction - (1) Native/White Topology; (2) Black Topology;
   and (3) Grey Topology.  Based on the local policy, the domain
   controller would share the domain topology to the Super Controller
   based on the abstraction type.  Note that any of the control plane or
   management plane mechanism could be used to carry abstracted domain
   topology.  The Super Controller's MDSC function is expected to manage
   a E2E topology by coordinating the abstracted domain topology
   received from the domain controllers.

3.2.  Path Computation/Path instantiation

   The Domain Controller is responsible for computing and setup of path
   when the source and destination is in the same domain, otherwise the
   Super Controller coordinates the multi-domain path computation and
   setup with the help of the domain controller.  This is aligned to
   ACTN.

   PCEP [RFC5440] provides mechanisms for Path Computation Elements
   (PCEs) [RFC4655] to perform path computations in response to Path
   Computation Clients (PCCs) requests.  Since then, the role and
   function of the PCE has grown to allow delegated control [RFC8231]
   and PCE-initiated use of network resources [RFC8281].

   Further, [RFC6805] and [I-D.ietf-pce-stateful-hpce] describes a
   hierarchy of PCE with Parent PCE coordinating multi-domain path
   computation function between Child PCE(s).  This fits well with HIC
   as described in this document.

   Note that a management plane interface which uses the YANG model for
   path computation/setup ([I-D.ietf-teas-yang-path-computation] and
   [I-D.ietf-teas-yang-te]) could be used in place of PCEP.

   In case there is a need to stitch per domain tunnels into an E2E
   tunnel, mechanism are described in [I-D.lee-pce-lsp-stitching-hpce]
   and [I-D.dugeon-pce-stateful-interdomain].







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3.3.  BGP considerations

   [RFC4456] describes the concept of route-reflection where a "route
   reflector" (RR) reflects the routes to avoid full mesh connection
   between Internal BGP (IBGP) peers.  The IP domain controller can play
   the role of RR in its domain.  The super controller can further act
   as RR to towards the domain controller.

   [Editor's Note: To do - BGP Policy, BGP Flowspec.  More information
   will be added in the next version]

   [Editor's Note: Need to evaluate a role of BMP]

4.  VPN Service

4.1.  Seamless MPLS

   Seamless MPLS [I-D.ietf-mpls-seamless-mpls] describes an architecture
   which can be used to extend MPLS networks to integrate access and
   core/aggregation networks into a single MPLS domain.In the seamless
   MPLS for mobile backhaul, since there are multiple domains including
   the core network and multiple mobile backhaul networks, for each
   domain there is a domain controller.  In order to implement the end-
   to-end network service provision, there should be coordination among
   multiple domain controllers.


























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                                |
                                |
                                |
                             +----------+
              |--------------|Super     |---------|
              |              |Controller|         |
              |              +----------+         |
              |                 |                 |
              |                 |                 |
              |                 |                 |
          +------+           +------+          +------+
     |----|DoCo  |----|  |---|DoCo  |--|  |----|DoCo  |---|
     |    |#X1   |    |  |   |#Y    |  |  |    |#X2   |   |
     |    +------+    |  |   +------+  |  |    +------+   |
     |                |  |             |  |               |
     |                |  |             |  |               |
     |                |  |             |  |               |
     |               +----+           +----+              |
     |           ....|ABR1|...........|ABR3|....          |
   +----+   .....    +----+           +----+    .....   +----+
   | PE |...                                         ...| PE |
   +----+   .....                                       +----+
                 ....+----+           +----+    .....
                     |ABR2|...........|ABR4|....
                     +----+           +----+

     |      IGP-X1     |      IGP-Y     |       IGP-X2     |
     |       (MBH)     |      (Core)    |       (MBH)      |
     |                 |                |                  |
     |-----BGP LSP-----|-----BGP LSP----|------BGP LSP-----|
     |                 |                |                  |
     |---LDP/TE LSP----|----LDP/TE LSP--|-----LDP/TE LSP---|
     |                 |                |                  |



                          Figure 3: Seamless MPLS

   Super Controller is responsible for setting the seamless MPLS
   service.  It should break down the service model to network
   configuration model [RFC8309] and the domain controller further break
   it to the device configuration model to the PE/ASBR to make the E2E
   seamless MPLS service.  The selection of appropriate ASBRs and
   handling of intra-domain tunnels is coordinated by the Super
   Controller in the similar fashion as shown in Section 4.2.

   By enabling BGP sessions between Domain Controller and Super
   Controller, BGP labeled routes can also be learned at Super



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   Controller.  As Super Controller is aware of the (abstract) topology,
   it could make intelligent decisions regarding E2E BGP LSP to optimize
   based on the overall traffic information.

4.2.  L3VPN

   A Layer 3 IP VPN service is a collection of sites that are authorized
   to exchange traffic between each other over a shared IP
   infrastructure.  [RFC4110] provides a framework for Layer 3 Provider-
   Provisioned Virtual Private Networks (PPVPNs).  [RFC8299] provides a
   L3VPN service delivery YANG model for PE-based VPNs.  The Super
   controller is expected to implement the L3SM model and translate it
   to network models towards the domain controller, which in terns
   translate it to the device model.  See [RFC8309] for more details.

                                     | L3SM
                                     V
                          +--------------------+
                          |  Super Controller  |
                          +--------------------+
                                     |
                     +-------------------------------+
                     |                               |
                     V                               V
                  +--------+                   +--------+
                  | DoCo#1 |                   | DoCo#2 |
                  |        |                   |        |
                  +--------+                   +--------+

            CE                                                   CE
             \     AS 100                          AS 200       /
              \                                               /
               A----B----C----ASBR1------ASBR2----D----E----F
              /    /    /       /          /     /    /    /
             /    /    /       /          /     /    /    /
      CE----G----H----I----ASBR3------ASBR4----J----K----L------CE

                              Figure 4: L3VPN

   Based on the user data in L3SM model, the network configurations need
   to be trickle down to the network device to setup the L3VPN.

   Based on the QoS or Policy requirement for the L3VPN service, the
   Super Controller may -

   o  Set the tunnel selection policy at the PE/ASBR routers so that
      they could select the existing tunnels




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   o  Select an existing tunnels at the controller level and bind it to
      the VPN service

   o  Initiate the process of creating a new tunnel based on the QoS
      requirement and bind it the VPN service

   o  Initiate the process of creating a new tunnel based on the the
      policy

   Refer [I-D.lee-teas-te-service-mapping-yang] for more details from
   ACTN perspective.

   Apart from the Management plane interface based on respective YANG
   models, the control plane interface PCEP could be used for path
   computation and setup.

4.3.  L2VPN and EVPN service

   There are two fundamentally different kinds of Layer 2 VPN service
   that a service provider could offer to a customer: Virtual Private
   Wire Service (VPWS) and Virtual Private LAN Service (VPLS) [RFC4664].
   A VPWS is a VPN service that supplies an L2 point-to-point service.
   A VPLS is an L2 service that emulates LAN service across a Wide Area
   Network (WAN).  A BGP MPLS-based Ethernet VPN (EVPN) [RFC7432]
   addresses some of the limitations when it comes to multihoming and
   redundancy, multicast optimization, provisioning simplicity, flow-
   based load balancing, and multipathing etc.

   The handling of L2VPN/EVPN service is done in a similar fashion as
   shown in Section 4.2.

5.  Possible Features/Extensions

   This sections list some of the possible features or protocol
   extensions that could be worked on to deploy HIC in a multi-domain
   packet network.

   1.  Simplify the initial configurations needed to setup the
       relationship between the super controller and the domain
       controllers.  Note that this could be done via exchanges during
       initial session establishment, discovery via other protocols,
       service discovery (such as DNS) etc.

   2.  The (higher-level controller, lover-level controller)
       relationship or the the role of the controller.

   3.  The learning and handling of various capabilities of the Super
       Controller and Domain Controller.



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   4.  Handling of multiple instances of controller at each level for
       high availability.

   [Editor's Note - This list is expected to be updated in next version
   with more details]

6.  Other Considerations

6.1.  Control Plane

6.1.1.  PCE / PCEP

   The Path Computation Element communication Protocol (PCEP) [RFC5440]
   provides mechanisms for Path Computation Elements (PCEs) [RFC4655] to
   perform path computations in response to Path Computation Clients
   (PCCs) requests.

   The ability to compute shortest constrained TE LSPs in Multiprotocol
   Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across
   multiple domains has been identified as a key motivation for PCE
   development.

   A stateful PCE [RFC8231] is capable of considering, for the purposes
   of path computation, not only the network state in terms of links and
   nodes (referred to as the Traffic Engineering Database or TED) but
   also the status of active services (previously computed paths, and
   currently reserved resources, stored in the Label Switched Paths
   Database (LSPDB).

   [RFC8051] describes general considerations for a stateful PCE
   deployment and examines its applicability and benefits, as well as
   its challenges and limitations through a number of use cases.

   [RFC8231] describes a set of extensions to PCEP to provide stateful
   control.  A stateful PCE has access to not only the information
   carried by the network's Interior Gateway Protocol (IGP), but also
   the set of active paths and their reserved resources for its
   computations.  The additional state allows the PCE to compute
   constrained paths while considering individual LSPs and their
   interactions.  [RFC8281] describes the setup, maintenance and
   teardown of PCE-initiated LSPs under the stateful PCE model.

   [RFC8231] also describes the active stateful PCE.  The active PCE
   functionality allows a PCE to reroute an existing LSP or make changes
   to the attributes of an existing LSP, or a PCC to delegate control of
   specific LSPs to a new PCE.





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   Computing paths across large multi-domain environments require
   special computational components and cooperation between entities in
   different domains capable of complex path computation.  The PCE
   provides an architecture and a set of functional components to
   address this problem space.  A PCE may be used to compute end-to-end
   paths across multi-domain environments using a per-domain path
   computation technique [RFC5152].  The Backward recursive PCE based
   path computation (BRPC) mechanism [RFC5441] defines a PCE-based path
   computation procedure to compute inter-domain constrained MPLS and
   GMPLS TE networks.  However, both per-domain and BRPC techniques
   assume that the sequence of domains to be crossed from source to
   destination is known, either fixed by the network operator or
   obtained by other means.

   [RFC6805] describes a Hierarchical PCE (H-PCE) architecture which can
   be used for computing end-to-end paths for inter-domain MPLS Traffic
   Engineering (TE) and GMPLS Label Switched Paths (LSPs) when the
   domain sequence is not known.  Within the Hierarchical PCE (H-PCE)
   architecture, the Parent PCE (P-PCE) is used to compute a multi-
   domain path based on the domain connectivity information.  A Child
   PCE (C-PCE) may be responsible for a single domain or multiple
   domains, it is used to compute the intra-domain path based on its
   domain topology information.

   [I-D.ietf-pce-stateful-hpce] state the considerations for stateful
   PCE(s) in hierarchical PCE architecture.  In particular, the behavior
   changes and additions to the existing stateful PCE mechanisms
   (including PCE- initiated LSP setup and active PCE usage) in the
   context of networks using the H-PCE architecture.

   [I-D.ietf-pce-applicability-actn] examines the applicability of PCE/
   PCEP to the ACTN framework in detail.

6.1.2.  BGP

   [Editor's Note - TBD, More details on BGP-LS, BGP-Flowspec, RR
   handling, BGP Policy etc to be added in the next revision]

6.2.  Management Plane

6.2.1.  YANG Models

   This is an non-exhaustive list of possible yang models developed or
   in-development that could be used for HIC.

      Topology: [I-D.ietf-i2rs-yang-network-topo] defines a generic YANG
      data model for network topology.  [I-D.ietf-teas-yang-te-topo]




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      defines a YANG data model for representing, retrieving and
      manipulating Traffic Engineering (TE) Topologies.

      Tunnel: [I-D.ietf-teas-yang-te] defines a YANG data model for the
      configuration and management of Traffic Engineering (TE)
      interfaces, tunnels and Label Switched Paths (LSPs).

      L3VPN: The Layer 3 service model (L3SM) is defined in [RFC8299],
      which is a YANG data model that can be used for communication
      between customers and network operators and to deliver a Layer 3
      provider-provisioned VPN service.  [I-D.ietf-bess-l3vpn-yang]
      defines a YANG data model that can be used to configure and manage
      BGP Layer 3 VPNs at the device.  Note that a network configuration
      model at the Domain Controller level needs to be developed.

      L2VPN/EVPN: [I-D.ietf-l2sm-l2vpn-service-model] defines a YANG
      data model that can be used to configure a Layer 2 Provider
      Provisioned VPN service.  This model is intended to be
      instantiated at management system to deliver the overall service.
      [I-D.ietf-bess-l2vpn-yang] and [I-D.ietf-bess-evpn-yang] defines a
      YANG data model to configure and manage L2VPN and EVPN service
      respectively.  Note that a network configuration model at the
      Domain Controller level needs to be developed.

      OAM: TBD

   [Editor's Note - the above list should be extended.]

6.2.2.  Protocol Considerations

   The Network Configuration Protocol (NETCONF) [RFC6241] provides
   mechanisms to install, manipulate, and delete the configuration of
   network devices.  The RESTCONF [RFC8040] describes an HTTP-based
   protocol that provides a programmatic interface for accessing data
   defined in YANG, using the data-store concepts defined in NETCONF.

   Some other mechanism like gRPC/gNMI could also be used between
   controllers using the same YANG data models.

7.  IANA Considerations

   There are no IANA concerns in this document.

8.  Security Considerations

   There are no new security concerns in this document.





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9.  Acknowledgments

10.  References

10.1.  Normative References

   [I-D.ietf-teas-actn-framework]
              Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
              Control of Traffic Engineered Networks", draft-ietf-teas-
              actn-framework-11 (work in progress), October 2017.

10.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4110]  Callon, R. and M. Suzuki, "A Framework for Layer 3
              Provider-Provisioned Virtual Private Networks (PPVPNs)",
              RFC 4110, DOI 10.17487/RFC4110, July 2005,
              <https://www.rfc-editor.org/info/rfc4110>.

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

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

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

   [RFC5152]  Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
              Per-Domain Path Computation Method for Establishing Inter-
              Domain Traffic Engineering (TE) Label Switched Paths
              (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008,
              <https://www.rfc-editor.org/info/rfc5152>.



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   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441,
              DOI 10.17487/RFC5441, April 2009,
              <https://www.rfc-editor.org/info/rfc5441>.

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

   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,
              <https://www.rfc-editor.org/info/rfc6805>.

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

   [RFC7491]  King, D. and A. Farrel, "A PCE-Based Architecture for
              Application-Based Network Operations", RFC 7491,
              DOI 10.17487/RFC7491, March 2015,
              <https://www.rfc-editor.org/info/rfc7491>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.









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   [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,
              <https://www.rfc-editor.org/info/rfc7926>.

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

   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/info/rfc8051>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

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

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
              <https://www.rfc-editor.org/info/rfc8309>.

   [I-D.ietf-teas-actn-yang]
              Lee, Y., zhenghaomian@huawei.com, z., Ceccarelli, D.,
              Yoon, B., and S. Belotti, "Applicability of YANG models
              for Abstraction and Control of Traffic Engineered
              Networks", draft-ietf-teas-actn-yang-01 (work in
              progress), February 2018.








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   [I-D.ietf-pce-applicability-actn]
              Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of
              Path Computation Element (PCE) for Abstraction and Control
              of TE Networks (ACTN)", draft-ietf-pce-applicability-
              actn-03 (work in progress), March 2018.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., and
              I. Bryskin, "A YANG Data Model for Traffic Engineering
              Tunnels and Interfaces", draft-ietf-teas-yang-te-12 (work
              in progress), February 2018.

   [I-D.ietf-teas-yang-te-topo]
              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Dios, "YANG Data Model for Traffic Engineering (TE)
              Topologies", draft-ietf-teas-yang-te-topo-15 (work in
              progress), February 2018.

   [I-D.ietf-i2rs-yang-network-topo]
              Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A Data Model for Network
              Topologies", draft-ietf-i2rs-yang-network-topo-20 (work in
              progress), December 2017.

   [I-D.ietf-pce-stateful-hpce]
              Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., King, D.,
              and O. Dios, "Hierarchical Stateful Path Computation
              Element (PCE).", draft-ietf-pce-stateful-hpce-02 (work in
              progress), October 2017.

   [I-D.ietf-teas-yang-path-computation]
              Busi, I., Belotti, S., Lopezalvarez, V., Dios, O.,
              ansharma@infinera.com, a., Shi, Y., Vilata, R.,
              Sethuraman, K., Scharf, M., and D. Ceccarelli, "Yang model
              for requesting Path Computation", draft-ietf-teas-yang-
              path-computation-00 (work in progress), November 2017.

   [I-D.ietf-mpls-seamless-mpls]
              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M., and D. Steinberg, "Seamless MPLS Architecture", draft-
              ietf-mpls-seamless-mpls-07 (work in progress), June 2014.

   [I-D.ietf-bess-evpn-yang]
              Brissette, P., Shah, H., Hussain, I., Tiruveedhula, K.,
              and J. Rabadan, "Yang Data Model for EVPN", draft-ietf-
              bess-evpn-yang-05 (work in progress), February 2018.





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   [I-D.ietf-bess-l2vpn-yang]
              Shah, H., Brissette, P., Chen, I., Hussain, I., Wen, B.,
              and K. Tiruveedhula, "YANG Data Model for MPLS-based
              L2VPN", draft-ietf-bess-l2vpn-yang-08 (work in progress),
              February 2018.

   [I-D.ietf-bess-l3vpn-yang]
              Jain, D., Patel, K., Brissette, P., Li, Z., Zhuang, S.,
              Liu, X., Haas, J., Esale, S., and B. Wen, "Yang Data Model
              for BGP/MPLS L3 VPNs", draft-ietf-bess-l3vpn-yang-02 (work
              in progress), October 2017.

   [I-D.ietf-l2sm-l2vpn-service-model]
              Wen, B., Fioccola, G., Xie, C., and L. Jalil, "A YANG Data
              Model for L2VPN Service Delivery", draft-ietf-l2sm-l2vpn-
              service-model-08 (work in progress), February 2018.

   [I-D.dhodylee-pce-pcep-ls]
              Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
              Distribution of Link-State and TE Information.", draft-
              dhodylee-pce-pcep-ls-09 (work in progress), January 2018.

   [I-D.lee-teas-te-service-mapping-yang]
              Lee, Y., Dhody, D., Ceccarelli, D., Tantsura, J., and G.
              Fioccola, "Traffic Engineering and Service Mapping Yang
              Model", draft-lee-teas-te-service-mapping-yang-06 (work in
              progress), February 2018.

   [I-D.lee-pce-lsp-stitching-hpce]
              Lee, Y., Dhody, D., and D. Ceccarelli, "PCEP Extensions
              for Stitching LSPs in Hierarchical Stateful PCE Model",
              draft-lee-pce-lsp-stitching-hpce-01 (work in progress),
              December 2017.

   [I-D.dugeon-pce-stateful-interdomain]
              Dugeon, O. and J. Meuric, "PCEP Extension for Stateful
              Inter-Domain Tunnels", draft-dugeon-pce-stateful-
              interdomain-00 (work in progress), October 2017.

Authors' Addresses

   Zhenbin Li
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   EMail: lizhenbin@huawei.com



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   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: dhruv.ietf@gmail.com


   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   EMail: huaimo.chen@huawei.com




































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