TEAS Working Group                                               I. Busi
Internet-Draft                                                  H. Zheng
Intended status: Standards Track                     Huawei Technologies
Expires: January 13, 2022                                         A. Guo
                                                          Futurewei Inc.
                                                                  X. Liu
                                                          Volta Networks
                                                           July 12, 2021


                 A YANG Data Model for MPLS-TE Topology
             draft-busizheng-teas-yang-te-mpls-topology-01

Abstract

   This document describes a YANG data model for Multi-Protocol Label
   Switching (MPLS) with Traffic Engineering (MPLS-TE) networks.

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
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   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 January 13, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   3
   2.  MPLS-TE Types Overview  . . . . . . . . . . . . . . . . . . .   3
   3.  MPLS-TE Topology Model Overview . . . . . . . . . . . . . . .   3
     3.1.  TE Label Augmentations  . . . . . . . . . . . . . . . . .   4
     3.2.  MPLS-TP Topology  . . . . . . . . . . . . . . . . . . . .   5
   4.  YANG model for common MPLS-TE Types . . . . . . . . . . . . .   6
   5.  YANG model for MPLS-TE Topology . . . . . . . . . . . . . . .   8
     5.1.  YANG Tree . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  YANG Code . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This document describes a YANG data model for Multi-Protocol Label
   Switching (MPLS) with Traffic Engineering (MPLS-TE) networks.

   This document also defines a collection of common data types and
   groupings in YANG data modeling language for MPLS-TE networks.  These
   derived common types and groupings are intended to be imported by the
   MPLS-TE topology model, defined in this document, as well as by the
   MPLS-TE tunnel model, defined in [I-D.ietf-teas-yang-te-mpls].

   Multi-Protocol Label Switching - Transport Profile (MPLS-TP) is a
   profile of the MPLS protocol that is used in packet switched
   transport networks and operated in a similar manner to other existing
   transport technologies (e.g., OTN), as described in [RFC5921].  The
   YANG model defined in this document can also be for MPLS-TP networks.

1.1.  Tree Diagram

   A simplified graphical representation of the data model is used in
   Section 5.1 of this this document.  The meaning of the symbols in
   these diagrams is defined in [RFC8340].





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1.2.  Prefixes in Data Node Names

   In this document, names of data nodes and other data model objects
   are prefixed using the standard prefix associated with the
   corresponding YANG imported modules, as shown in Table 1.

   +--------------+----------------------+-----------------------------+
   | Prefix       | YANG module          | Reference                   |
   +--------------+----------------------+-----------------------------+
   | rt-types     | ietf-routing-types   | [RFC8294]                   |
   |              |                      |                             |
   | tet          | ietf-te-topology     | [RFC8795]                   |
   |              |                      |                             |
   | tet-pkt      | ietf-te-topology-    | [I-D.ietf-teas-yang-l3-te-t |
   |              | packet               | opo]                        |
   |              |                      |                             |
   | te-packet-   | ietf-te-packet-types | [I-D.ietf-teas-yang-l3-te-t |
   | types        |                      | opo]                        |
   |              |                      |                             |
   | mte-types    | ietf-mpls-te-types   | This document               |
   |              |                      |                             |
   | tet-mpls     | ietf-te-mpls-        | This document               |
   |              | topology             |                             |
   +--------------+----------------------+-----------------------------+

             Table 1: Prefixes and corresponding YANG modules

2.  MPLS-TE Types Overview

   The module ietf-mpls-te-types contains the following YANG types and
   groupings which can be reused by MPLS-TE YANG models:

   load-balancing-type  This identify defines the types of load-
      balancing algorithms used on bundled MPLS-TE link.

   te-mpls-label-hop  This grouping is used for the augmentation of TE
      label for MPLS-TE path.

3.  MPLS-TE Topology Model Overview

   The MPLS-TE technology specific topology model augments the ietf-te-
   topology-packet YANG module, defined in
   [I-D.ietf-teas-yang-l3-te-topo], which in turns augment the generic
   ietf-te-topology YANG module, defined in [RFC8795], as shown in
   Figure 1.






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                     +------------------+    o: augment
        TE generic   | ietf-te-topology |
                     +------------------+
                               o
                               |
                               |
                               |
                  +-------------------------+
        Packet TE | ietf-te-topology-packet |
                  +-------------------------+
                               o
                               |
                               |
                               |
                   +-----------------------+
        MPLS-TE    | ietf-te-mpls-topology |
                   +-----------------------+

     Figure 1: Relationship between MPLS-TE, Packet-TE and TE topology
                                  models

   Given the guidance for augmentation in [RFC8795], the following
   technology-specific augmentations need to be provided:

   o  A network-type to indicate that the TE topology is an MPLS-TE
      Topology, as follow:

        augment /nw:networks/nw:network/nw:network-types/tet:te-topology
                /tet-pkt:packet:
          +--rw mpls-topology!

   o  TE Label Augmentations as described in Section 3.1.

   Note: TE Bandwidth Augmentations for paths, LSPs and links are
   provided by the ietf-te-topology-packet module, defined in
   [I-D.ietf-teas-yang-l3-te-topo].

3.1.  TE Label Augmentations

   In MPLS-TE, the label allocation is done by NE, information about
   label values availability is not necessary to be provided to the
   controller.  Moreover, MPLS-TE tunnels are currently established
   within a single domain.

   Therefore this document does not define any MPLS-TE technology-
   specific augmentations, of the TE Topology model, for the TE label
   since no TE label related attributes should be instantiated for MPLS-
   TE Topologies.



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   Open issue: shall this module allows the setup of MPLS-TE multi-
   domain tunnels?

3.2.  MPLS-TP Topology

   Multi-Protocol Label Switching - Transport Profile (MPLS-TP) is a
   profile of the MPLS protocol that is used in packet switched
   transport networks and operated in a similar manner to other existing
   transport technologies (e.g., OTN), as described in [RFC5921].

   Therefore YANG model defined in this document can also be applicable
   for MPLS-TP networks.

   However, as described in [RFC5921], MPLS-TP networks support
   bidirectional LSPs and require no ECMP and no PHP.  When reporting
   the topology for an MPLS-TP network, additional information is
   required to indicate whether the network support these MPLS-TP
   characteristics.

   It is worth noting that [RFC8795] is already capable to model TE
   topologies supporting either unidirectional or bidirectional LSPs:
   all bidirectional TE links can support bidirectional LSPs and all the
   links can support unidirectional LSPs and it is always possible to
   associated unidirectional LSPs as long as they belong to the same
   tunnel.

   When setting up bidirectional LSPs (e.g., MPLS-TP LSPs) only
   bidirectional TE Links are selected by path computation.

   In order to allow reporting that ECMP is not affecting forwarding the
   packets of a given LSP, the load-balancing-type attribute reports
   whether a LAG or TE Bundled Link performs load-balancing on a per-
   flow or per-top-label:

       augment /nw:networks/nw:network/nt:link/tet:te:
         +--rw load-balancing-type?   mte-types:load-balancing-type

   When setting up LSPs which do not requires ECMP (e.g., MPLS-TP LSPs)
   only Links that are not part of a LAG or TE Bundle or that performs
   per-top-label load balancing are selected by path computation.

   It is assumed that almost all the MPLS-TE nodes are capable to
   support Ultimate Hop Popping (UHP).  However, if some interfaces are
   not able to support UHP, they can report it in the MPLS-TE topology:

       augment /nw:networks/nw:network/nw:node/nt:termination-point
               /tet:te:
         +--ro uhp-incapable?   empty



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   When setting up LSPs which do not requires PHP (e.g., MPLS-TP LSPs)
   only the interfaces (LTPs) which are capable to support UHP in the
   destination node are selected by path computation.

4.  YANG model for common MPLS-TE Types

   <CODE BEGINS>file "ietf-mpls-te-types@2021-07-12.yang"
   module ietf-mpls-te-types {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-mpls-te-types";

     prefix "mte-types";

     import ietf-routing-types {
       prefix "rt-types";
     }

     organization
       "Internet Engineering Task Force (IETF) TEAS WG";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/teas/>
        WG List:  <mailto:teas@ietf.org>

        Editor: Italo Busi
          <mailto:italo.busi@huawei.com>

        Editor: Haomian Zheng
          <mailto:zhenghaomian@huawei.com>

        Editor: Aihua Guo
          <mailto:aihuaguo.ietf@gmail.com>

        Editor: Xufeng Liu
          <mailto:xufeng.liu.ietf@gmail.com>";

     description
       "This module defines technology-specific MPLS-TE types
        data model.

        Copyright (c) 2021 IETF Trust and the persons identified
        as authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with
        or without modification, is permitted pursuant to, and
        subject to the license terms contained in, the Simplified
        BSD License set forth in Section 4.c of the IETF Trust's
        Legal Provisions Relating to IETF Documents
        (http://trustee.ietf.org/license-info).



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        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2021-07-12 {
       description
         "Initial Version";
       reference
         "draft-busizheng-teas-yang-te-mpls-topology";
     }

     /*
     * Typedefs
     */

     typedef load-balancing-type {
       type enumeration {
         enum per-flow {
           description
             "The load-balancing algorithm ensures that packets
              characterized as the same flow (e.g. based on IP 5-tuple)
              that egress on a LAG or a bundled TE link are forwarded
              on the same component link.

              Packets for different flows within the same LSP can be
              forwarded on different component links.";
         }
         enum per-top-label {
           description
             "The load-balancing algorithm ensures incoming MPLS
              packets with the same top MPLS label and that egress on
              on a LAG or bundled TE link are forwarded on the same
              component link.

              Packets for different flows within the same LSP are
              forwarded on the same component link.";
         }
       }
       description
         "The type of load balancing used on bundled links.";
     }  // typedef load-balancing-type

     /*
     * Groupings
     */

     grouping te-mpls-label-hop {
       description
         "MPLS-TE Label Hop.";



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       leaf mpls-label {
         type rt-types:mpls-label;
         description
           "MPLS Label.";
       }
     }  // grouping te-mpls-label-hop
   }
   <CODE ENDS>

                    Figure 2: MPLS-TE Types YANG model

5.  YANG model for MPLS-TE Topology

5.1.  YANG Tree

   Figure 3 below shows the tree diagram of the YANG model defined in
   module ietf-te-mpls-topology.yang.

   module: ietf-te-mpls-topology

     augment /nw:networks/nw:network/nw:network-types/tet:te-topology
               /tet-pkt:packet:
       +--rw mpls-topology!
     augment /nw:networks/nw:network/nt:link/tet:te:
       +--rw load-balancing-type?   mte-types:load-balancing-type
     augment /nw:networks/nw:network/nw:node/nt:termination-point
               /tet:te:
       +--ro uhp-incapable?   empty

                   Figure 3: MPLS-TE topology YANG tree

5.2.  YANG Code

   <CODE BEGINS>file "ietf-te-mpls-topology@2021-07-12.yang"
   module ietf-te-mpls-topology {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-te-mpls-topology";

     prefix "tet-mpls";

     import ietf-network {
       prefix "nw";
     }

     import ietf-network-topology {
       prefix "nt";
     }




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     import ietf-te-topology {
       prefix "tet";
     }

     import ietf-te-topology-packet {
       prefix "tet-pkt";
     }

     import ietf-mpls-te-types {
       prefix "mte-types";
     }

     organization
       "Internet Engineering Task Force (IETF) TEAS WG";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/teas/>
        WG List:  <mailto:teas@ietf.org>

        Editor: Italo Busi
          <mailto:italo.busi@huawei.com>

        Editor: Haomian Zheng
          <mailto:zhenghaomian@huawei.com>

        Editor: Aihua Guo
          <mailto:aihuaguo.ietf@gmail.com>

        Editor: Xufeng Liu
          <mailto:xufeng.liu.ietf@gmail.com>";

     description
       "This module defines technology-specific MPLS-TE topology
        data model.

        Copyright (c) 2021 IETF Trust and the persons identified
        as authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with
        or without modification, is permitted pursuant to, and
        subject to the license terms contained in, the Simplified
        BSD License set forth in Section 4.c of the IETF Trust's
        Legal Provisions Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2021-07-12 {



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       description
         "Initial Version";
       reference
         "draft-busizheng-teas-yang-te-mpls-topology";
     }

     /*
      * Augmentations
      */

     augment "/nw:networks/nw:network/nw:network-types/"
           + "tet:te-topology/tet-pkt:packet" {
       description
         "Augment network types to include MPLS-TE Topology Type";
       container mpls-topology {
         presence
           "Indicates an MPLS-TE Topology Type.";
         description
           "Its presence indicates an MPLS-TE Topology";
       }
     }

     augment "/nw:networks/nw:network/nt:link/tet:te" {
       when "../../nw:network-types/tet:te-topology/"
          + "tet-pkt:packet/tet-mpls:mpls-topology"  {
         description
           "Augment MPLS-TE Topology.";
       }
       description
         "Augment TE Link.";

       leaf load-balancing-type {
         type mte-types:load-balancing-type;
         default 'per-flow';
         description
           "Indicates the type of load-balancing (per-flow or per-LSP)
            performed by the bundled TE Link.

            This leaf is not present when the TE Link is not bundled.";
       }  // leaf load-balancing-type
     }

     augment "/nw:networks/nw:network/nw:node/nt:termination-point/"
           + "tet:te" {
       when "../../../nw:network-types/tet:te-topology/"
          + "tet-pkt:packet/tet-mpls:mpls-topology" {
         description "Augment MPLS-TE Topology.";
       }



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       description "Augment LTP.";

       leaf uhp-incapable {
         type empty;
         config false;
         description
           "When present, indicates that the LTP is not capable to
            support Ultimate Hop Popping (UHP).";
       }   // leaf uhp-incapable
     }
   }
   <CODE ENDS>

                  Figure 4: MPLS-TE topology YANG module

6.  Security Considerations

   To be added.

7.  IANA Considerations

   To be added.

8.  References

8.1.  Normative References

   [I-D.ietf-teas-yang-l3-te-topo]
              Liu, X., Bryskin, I., Beeram, V. P., Saad, T., Shah, H.,
              and O. G. D. Dios, "YANG Data Model for Layer 3 TE
              Topologies", draft-ietf-teas-yang-l3-te-topo-11 (work in
              progress), July 2021.

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

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

   [RFC8795]  Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Gonzalez de Dios, "YANG Data Model for Traffic
              Engineering (TE) Topologies", RFC 8795,
              DOI 10.17487/RFC8795, August 2020,
              <https://www.rfc-editor.org/info/rfc8795>.




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8.2.  Informative References

   [I-D.ietf-teas-yang-te-mpls]
              Saad, T., Gandhi, R., Liu, X., Beeram, V. P., and I.
              Bryskin, "A YANG Data Model for MPLS Traffic Engineering
              Tunnels", draft-ietf-teas-yang-te-mpls-03 (work in
              progress), March 2020.

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
              <https://www.rfc-editor.org/info/rfc5921>.

Acknowledgments

   The authors would also like to thank Tarek Saad, Vishnu Pavan Beeram,
   Rakesh Gandhi, Xufeng Liu, Igor Bryskin for their input on how to
   support MPLS-TP features (bidirectional LSPs, no ECMP, no PHP) using
   a common MPLS-TE topology model.

   We thank Loa Andersson and Igor Bryskin for providing useful
   suggestions for this draft.

   This document was prepared using kramdown.

   Previous versions of this document was prepared using 2-Word-
   v2.0.template.dot.

Authors' Addresses

   Italo Busi
   Huawei Technologies

   Email: italo.busi@huawei.com


   Haomian Zheng
   Huawei Technologies

   Email: zhenghaomian@huawei.com


   Aihua Guo
   Futurewei Inc.

   Email: aihuaguo.ietf@gmail.com





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   Xufeng Liu
   Volta Networks

   Email: xufeng.liu.ietf@gmail.com















































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