path: root/doc/rfc/rfc9270.txt

Internet Engineering Task Force (IETF)                             J. He
Request for Comments: 9270                                       I. Busi
Updates: 4872, 4873                                  Huawei Technologies
Category: Standards Track                                        J. Ryoo
ISSN: 2070-1721                                                  B. Yoon
                                                                    ETRI
                                                                 P. Park
                                                                      KT
                                                             August 2022


         GMPLS Signaling Extensions for Shared Mesh Protection

Abstract

   ITU-T Recommendation G.808.3 defines the generic aspects of a Shared
   Mesh Protection (SMP) mechanism, where the difference between SMP and
   Shared Mesh Restoration (SMR) is also identified.  ITU-T
   Recommendation G.873.3 defines the protection switching operation and
   associated protocol for SMP at the Optical Data Unit (ODU) layer.
   RFC 7412 provides requirements for any mechanism that would be used
   to implement SMP in a Multi-Protocol Label Switching - Transport
   Profile (MPLS-TP) network.

   This document updates RFCs 4872 and 4873 to provide extensions for
   Generalized Multi-Protocol Label Switching (GMPLS) signaling to
   support the control of the SMP mechanism.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9270.

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Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  SMP Definition
   4.  Operation of SMP with GMPLS Signaling Extensions
   5.  GMPLS Signaling Extensions for SMP
     5.1.  Identifiers
     5.2.  Signaling Primary LSPs
     5.3.  Signaling Secondary LSPs
     5.4.  SMP Preemption Priority
     5.5.  Availability of Shared Resources: The Notify Message
     5.6.  SMP APS Configuration
   6.  Updates to PROTECTION Object
     6.1.  New Protection Type
     6.2.  Updates to Definitions of Notification and Operational Bits
     6.3.  Preemption Priority
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   RFC 4872 [RFC4872] defines extensions for Resource Reservation
   Protocol - Traffic Engineering (RSVP-TE) to support Shared Mesh
   Restoration (SMR) mechanisms.  SMR can be seen as a particular case
   of preplanned Label Switched Path (LSP) rerouting that reduces the
   recovery resource requirements by allowing multiple protecting LSPs
   to share common link and node resources.  The recovery resources for
   the protecting LSPs are pre-reserved during the provisioning phase,
   and explicit restoration signaling is required to activate (i.e.,
   commit resource allocation at the data plane) a specific protecting
   LSP that was instantiated during the provisioning phase.  RFC 4873
   [RFC4873] details the encoding of the last 32-bit Reserved field of
   the PROTECTION object defined in [RFC4872].

   ITU-T Recommendation G.808.3 [G808.3] defines the generic aspects of
   a Shared Mesh Protection (SMP) mechanism, which are not specific to a
   particular network technology in terms of architecture types,
   preemption principle, path monitoring methods, etc.  ITU-T
   Recommendation G.873.3 [G873.3] defines the protection switching
   operation and associated protocol for SMP at the Optical Data Unit
   (ODU) layer.  RFC 7412 [RFC7412] provides requirements for any
   mechanism that would be used to implement SMP in a Multi-Protocol
   Label Switching - Transport Profile (MPLS-TP) network.

   SMP differs from SMR in the activation/protection switching
   operation.  The former activates a protecting LSP via the Automatic
   Protection Switching (APS) protocol in the data plane when the
   working LSP fails, while the latter does it via control plane
   signaling.  It is therefore necessary to distinguish SMP from SMR
   during provisioning so that each node involved behaves appropriately
   in the recovery phase when activation of a protecting LSP is done.
   SMP has advantages with regard to the recovery speed compared with
   SMR.

   This document updates [RFC4872] and [RFC4873] to provide extensions
   for Generalized Multi-Protocol Label Switching (GMPLS) signaling to
   support the control of the SMP mechanism.  Specifically, it

   *  defines a new LSP Protection Type, "Shared Mesh Protection", for
      the LSP Flags field [RFC4872] of the PROTECTION object (see
      Section 6.1),

   *  updates the definitions of the Notification (N) and Operational
      (O) fields [RFC4872] of the PROTECTION object to take the new SMP
      type into account (see Section 6.2), and

   *  updates the definition of the 16-bit Reserved field [RFC4873] of
      the PROTECTION object to allocate 8 bits to signal the SMP
      preemption priority (see Section 6.3).

   Only the generic aspects for signaling SMP are addressed by this
   document.  The technology-specific aspects are expected to be
   addressed by other documents.

   RFC 8776 [RFC8776] defines a collection of common YANG data types for
   Traffic Engineering (TE) configuration and state capabilities.  It
   defines several identities for LSP Protection Types.  As this
   document introduces a new LSP Protection Type, [RFC8776] is expected
   to be updated to support the SMP mechanism specified in this
   document.  [YANG-TE] defines a YANG data model for the provisioning
   and management of TE tunnels, LSPs, and interfaces.  It includes some
   protection and restoration data nodes relevant to this document.
   Management aspects of the SMP mechanism are outside the scope of this
   document, and they are expected to be addressed by other documents.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   In addition, the reader is assumed to be familiar with the
   terminology used in [RFC4872], RFC 4426 [RFC4426], and RFC 6372
   [RFC6372].

3.  SMP Definition

   [G808.3] defines the generic aspects of an SMP mechanism.  [G873.3]
   defines the protection switching operation and associated protocol
   for SMP at the ODU layer.  [RFC7412] provides requirements for any
   mechanism that would be used to implement SMP in an MPLS-TP network.

   The SMP mechanism is based on precomputed protecting LSPs that are
   preconfigured into the network elements.  Preconfiguration here means
   pre-reserving resources for the protecting LSPs without activating a
   particular protecting LSP (e.g., in circuit networks, the cross-
   connects in the intermediate nodes of the protecting LSP are not
   preestablished).  Preconfiguring but not activating protecting LSPs
   allows link and node resources to be shared by the protecting LSPs of
   multiple working LSPs (which are themselves disjoint and thus
   unlikely to fail simultaneously).  Protecting LSPs are activated in
   response to failures of working LSPs or operator commands by means of
   the APS protocol, which operates in the data plane.  The APS protocol
   messages are exchanged along the protecting LSP.  SMP is always
   revertive.

   SMP is very similar to SMR, except that activation in the case of SMR
   is achieved by control plane signaling during the recovery operation,
   while the same is done for SMP by the APS protocol in the data plane.

4.  Operation of SMP with GMPLS Signaling Extensions

   Consider the network topology shown in Figure 1:

                             A---B---C---D
                              \         /
                               E---F---G
                              /         \
                             H---I---J---K

                  Figure 1: An Example of an SMP Topology

   The working LSPs [A,B,C,D] and [H,I,J,K] could be protected by the
   protecting LSPs [A,E,F,G,D] and [H,E,F,G,K], respectively.  Per RFC
   3209 [RFC3209], in order to achieve resource sharing during the
   signaling of these protecting LSPs, they have the same Tunnel
   Endpoint Address (as part of their SESSION object).  However, these
   addresses are not the same in this example.  Similar to SMR, this
   document defines a new LSP Protection Type of the secondary LSP as
   "Shared Mesh Protection" (see Section 6.1) to allow resource sharing
   along nodes E, F, and G.  Examples of shared resources include the
   capacity of a link and the cross-connects in a node.  In this case,
   the protecting LSPs are not merged (which is useful, since the paths
   diverge at G), but the resources along E, F, and G can be shared.

   When a failure, such as Signal Fail (SF) or Signal Degrade (SD),
   occurs on one of the working LSPs (say, working LSP [A,B,C,D]), the
   end node (say, node A) that detects the failure initiates the
   protection switching operation.  End node A will send a protection
   switching request APS message (for example, SF) to its adjacent
   (downstream) intermediate node (say, node E) to activate the
   corresponding protecting LSP and will wait for a confirmation message
   from node E.

   If the protection resource is available, node E will send the
   confirmation APS message to the end node (node A) and forward the
   switching request APS message to its adjacent (downstream) node (say,
   node F).  When the confirmation APS message is received by node A,
   the cross-connection on node A is established.  At this time, traffic
   is bridged to and selected from the protecting LSP at node A.  After
   forwarding the switching request APS message, node E will wait for a
   confirmation APS message from node F, which triggers node E to set up
   the cross-connection for the protecting LSP being activated.

   If the protection resource is not available (due to failure or being
   used by higher-priority connections), the switching will not be
   successful; the intermediate node (node E) MUST send a message to
   notify the end node (node A) (see Section 5.5).  If the resource is
   in use by a lower-priority protecting LSP, the lower-priority service
   will be removed, and the intermediate node will then follow the
   procedure as described for the case when the protection resource is
   available for the higher-priority protecting LSP.

   If node E fails to allocate the protection resource, it MUST send a
   message to notify node A (see Section 5.5).  Then, node A will stop
   bridging and selecting traffic to/from the protecting LSP and proceed
   with the procedure of removing the protection allocation according to
   the APS protocol.

5.  GMPLS Signaling Extensions for SMP

   The following subsections detail how LSPs using SMP can be signaled
   in an interoperable fashion using GMPLS RSVP-TE extensions (see RFC
   3473 [RFC3473]).  This signaling enables:

   (1)  the ability to identify a "secondary protecting LSP" (LSP
        [A,E,F,G,D] or LSP [H,E,F,G,K] from Figure 1, here called the
        "secondary LSP") used to recover another "primary working LSP"
        (LSP [A,B,C,D] or LSP [H,I,J,K] from Figure 1, here called the
        "protected LSP"),

   (2)  the ability to associate the secondary LSP with the protected
        LSP,

   (3)  the capability to include information about the resources used
        by the protected LSP while instantiating the secondary LSP,

   (4)  the capability to instantiate several secondary LSPs efficiently
        during the provisioning phase, and

   (5)  the capability to support activation of a secondary LSP via the
        APS protocol in the data plane if a failure occurs.

5.1.  Identifiers

   To simplify association operations, both LSPs (i.e., the protected
   LSP and the secondary LSP) belong to the same session.  Thus, the
   SESSION object MUST be the same for both LSPs.  The LSP ID, however,
   MUST be different to distinguish between the protected LSP and the
   secondary LSP.

   A new LSP Protection Type, "Shared Mesh Protection", is defined (see
   Section 6.1) for the LSP Flags field of the PROTECTION object (see
   [RFC4872]) to set up the two LSPs.  This LSP Protection Type value is
   only applicable to bidirectional LSPs as required in [G808.3].

5.2.  Signaling Primary LSPs

   The PROTECTION object (see [RFC4872]) is included in the Path message
   during signaling of the primary working LSPs, with the LSP Protection
   Type value set to "Shared Mesh Protection".

   Primary working LSPs are signaled by setting in the PROTECTION object
   the S bit to 0, the P bit to 0, and the N bit to 1; and setting in
   the ASSOCIATION object the Association ID to the associated secondary
   protecting LSP_ID.

      |  Note: The N bit is set to indicate that the protection
      |  switching signaling is done via the data plane.

5.3.  Signaling Secondary LSPs

   The PROTECTION object (see [RFC4872]) is included in the Path message
   during signaling of the secondary protecting LSPs, with the LSP
   Protection Type value set to "Shared Mesh Protection".

   Secondary protecting LSPs are signaled by setting in the PROTECTION
   object the S bit, the P bit, and the N bit to 1; and setting in the
   ASSOCIATION object the Association ID to the associated primary
   working LSP_ID, which MUST be known before signaling of the secondary
   LSP.  Moreover, the Path message used to instantiate the secondary
   LSP MUST include at least one PRIMARY_PATH_ROUTE object (see
   [RFC4872]) that further allows for recovery resource sharing at each
   intermediate node along the secondary path.

   With this setting, the resources for the secondary LSP MUST be pre-
   reserved but not committed at the data plane level, meaning that the
   internals of the switch need not be established until explicit action
   is taken to activate this LSP.  Activation of a secondary LSP and
   protection switching to the activated protecting LSP is done using
   the APS protocol in the data plane.

   After protection switching completes, the protecting LSP MUST be
   signaled by setting the S bit to 0 and the O bit to 1 in the
   PROTECTION object.  At this point, the link and node resources MUST
   be allocated for this LSP, which becomes a primary LSP (ready to
   carry traffic).  The formerly working LSP MAY be signaled with the A
   bit set in the ADMIN_STATUS object (see [RFC3473]).

   Support for extra traffic in SMP is left for further study.
   Therefore, mechanisms to set up LSPs for extra traffic are outside
   the scope of this document.

5.4.  SMP Preemption Priority

   The SMP preemption priority of a protecting LSP is used by the APS
   protocol to resolve competition for shared resources among multiple
   protecting LSPs and is indicated in the Preemption Priority field of
   the PROTECTION object in the Path message of the protecting LSP.

   The Setup and Holding priorities in the SESSION_ATTRIBUTE object can
   be used by GMPLS to control LSP preemption, but they are not used by
   the APS to resolve competition among multiple protecting LSPs.  This
   avoids the need to define a complex policy for defining Setup and
   Holding priorities when used for both GMPLS control plane LSP
   preemption and SMP shared resource competition resolution.

   When an intermediate node on the protecting LSP receives the Path
   message, the priority value in the Preemption Priority field MUST be
   stored for that protecting LSP.  When resource competition among
   multiple protecting LSPs occurs, the APS protocol will use their
   priority values to resolve this competition.  A lower value has a
   higher priority.

   In SMP, a preempted LSP MUST NOT be terminated even after its
   resources have been deallocated.  Once the working LSP and the
   protecting LSP are configured or preconfigured, the end node MUST
   keep refreshing both working and protecting LSPs, regardless of
   failure or preemption status.

5.5.  Availability of Shared Resources: The Notify Message

   When a lower-priority protecting LSP is preempted, the intermediate
   node that performed the preemption MUST send a Notify message with
   error code "Notify Error" (25) (see [RFC4872]) and error sub-code
   "Shared resources unavailable" (17) to the end nodes of that
   protecting LSP.  Upon receipt of this Notify message, the end node
   MUST stop sending and selecting traffic to/from its protecting LSP
   and try switching the traffic to another protecting LSP, if
   available.

   When a protecting LSP occupies the shared resources and they become
   unavailable, the same Notify message MUST be generated by the
   intermediate node to all the end nodes of the protecting LSPs that
   have lower SMP preemption priorities than the one that has occupied
   the shared resources.  If the shared resources become unavailable due
   to a failure in the shared resources, the same Notify message MUST be
   generated by the intermediate node to all the end nodes of the
   protecting LSPs that have been configured to use the shared
   resources.  In the case of a failure of the working LSP, these end
   nodes MUST avoid trying to switch traffic to these protecting LSPs
   that have been configured to use the shared resources and try
   switching the traffic to other protecting LSPs, if available.

   When the shared resources become available, a Notify message with
   error code "Notify Error" (25) and error sub-code "Shared resources
   available" (18) MUST be generated by the intermediate node.  The
   recipients of this Notify message are the end nodes of the lower-
   priority protecting LSPs that have been preempted and/or all the end
   nodes of the protecting LSPs that have lower SMP preemption
   priorities than the one that does not need the shared resources
   anymore.  Upon receipt of this Notify message, the end node is
   allowed to reinitiate the protection switching operation as described
   in Section 4, if it still needs the protection resource.

5.6.  SMP APS Configuration

   SMP relies on APS protocol messages being exchanged between the nodes
   along the path to activate a protecting LSP.

   In order to allow the exchange of APS protocol messages, an APS
   channel has to be configured between adjacent nodes along the path of
   the protecting LSP.  This is done by means other than GMPLS
   signaling, before any protecting LSP has been set up.  Therefore,
   there are likely additional requirements for APS configuration that
   are outside the scope of this document.

   Depending on the APS protocol message format, the APS protocol may
   use different identifiers than GMPLS signaling to identify the
   protecting LSP.

   Since the APS protocol is left for further study per [G808.3], it can
   be assumed that the APS message format and identifiers are technology
   specific and/or vendor specific.  Therefore, additional requirements
   for APS configuration are outside the scope of this document.

6.  Updates to PROTECTION Object

   GMPLS extension requirements for SMP introduce several updates to the
   PROTECTION object (see [RFC4872]), as detailed below.

6.1.  New Protection Type

   A new LSP Protection Type, "Shared Mesh Protection", is added in the
   PROTECTION object.  This LSP Protection Type value is only applicable
   to bidirectional LSPs.

   LSP (Protection Type) Flags:

      0x20: Shared Mesh Protection

   The rules defined in Section 14.2 of [RFC4872] ensure that all the
   nodes along an SMP LSP are SMP aware.  Therefore, there are no
   backward-compatibility issues.

6.2.  Updates to Definitions of Notification and Operational Bits

   The definitions of the N and O bits in Section 14.1 of [RFC4872] are
   replaced as follows:

   Notification (N): 1 bit

      When set to 1, this bit indicates that the control plane message
      exchange is only used for notification during protection
      switching.  When set to 0 (default), it indicates that the control
      plane message exchanges are used for purposes of protection
      switching.  The N bit is only applicable when the LSP Protection
      Type Flag is set to 0x04 (1:N Protection with Extra-Traffic), 0x08
      (1+1 Unidirectional Protection), 0x10 (1+1 Bidirectional
      Protection), or 0x20 (Shared Mesh Protection).  The N bit MUST be
      set to 0 in any other case.  If 0x20 (SMP), the N bit MUST be set
      to 1.

   Operational (O): 1 bit

      When set to 1, this bit indicates that the protecting LSP is
      carrying traffic after protection switching.  The O bit is only
      applicable when (1) the P bit is set to 1 and (2) the LSP
      Protection Type Flag is set to 0x04 (1:N Protection with Extra-
      Traffic), 0x08 (1+1 Unidirectional Protection), 0x10 (1+1
      Bidirectional Protection), or 0x20 (Shared Mesh Protection).  The
      O bit MUST be set to 0 in any other case.

6.3.  Preemption Priority

   [RFC4872] reserved a 32-bit field in the PROTECTION object header.
   Subsequently, [RFC4873] allocated several bits from that field and
   left the remainder of the bits reserved.  This specification further
   allocates the Preemption Priority field from the remaining formerly
   reserved bits.  The 32-bit field in the PROTECTION object as defined
   in [RFC4872] and modified by [RFC4873] is updated by this document as
   follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |I|R|   Reserved    | Seg.Flags |   Reserved    | Preempt Prio  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Preemption Priority (Preempt Prio): 8 bits

      This field indicates the SMP preemption priority of a protecting
      LSP, when the LSP Protection Type field indicates "Shared Mesh
      Protection".  The SMP preemption priority value is configured at
      the end nodes of the protecting LSP by a network operator.  A
      lower value has a higher priority.  The decision regarding how
      many priority levels should be implemented in an SMP network is
      left to network operators.

   See [RFC4873] for the definitions of the other fields.

7.  IANA Considerations

   IANA maintains a group of registries called "Resource Reservation
   Protocol (RSVP) Parameters", which includes the "Error Codes and
   Globally-Defined Error Value Sub-Codes" registry.  IANA has added the
   following values to the "Sub-Codes - 25 Notify Error" subregistry,
   which lists error value sub-codes that may be used with error code
   25.  IANA has allocated the following error value sub-codes (Table 1)
   for use with this error code as described in this document.

           +=======+==============================+===========+
           | Value | Description                  | Reference |
           +=======+==============================+===========+
           | 17    | Shared resources unavailable | RFC 9270  |
           +-------+------------------------------+-----------+
           | 18    | Shared resources available   | RFC 9270  |
           +-------+------------------------------+-----------+

                       Table 1: New Error Sub-Codes

8.  Security Considerations

   Since this document makes use of the exchange of RSVP messages that
   include a Notify message, the security threats discussed in [RFC4872]
   also apply to this document.

   Additionally, it may be possible to cause disruption to traffic on
   one protecting LSP by targeting a link used by the primary LSP of
   another, higher-priority LSP somewhere completely different in the
   network.  For example, in Figure 1, assume that the preemption
   priority of LSP [A,E,F,G,D] is higher than that of LSP [H,E,F,G,K]
   and the protecting LSP [H,E,F,G,K] is being used to transport
   traffic.  If link B-C is attacked, traffic on LSP [H,E,F,G,K] can be
   disrupted.  For this reason, it is important not only to use security
   mechanisms as discussed in [RFC4872] but also to acknowledge that
   detailed knowledge of a network's topology, including routes and
   priorities of LSPs, can help an attacker better target or improve the
   efficacy of an attack.

9.  References

9.1.  Normative References

   [G808.3]   International Telecommunication Union, "Generic protection
              switching - Shared mesh protection", ITU-T Recommendation
              G.808.3, October 2012,
              <https://www.itu.int/rec/T-REC-G.808.3>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              DOI 10.17487/RFC3473, January 2003,
              <https://www.rfc-editor.org/info/rfc3473>.

   [RFC4426]  Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
              Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery Functional Specification", RFC 4426,
              DOI 10.17487/RFC4426, March 2006,
              <https://www.rfc-editor.org/info/rfc4426>.

   [RFC4872]  Lang, J P., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
              Ed., "RSVP-TE Extensions in Support of End-to-End
              Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
              <https://www.rfc-editor.org/info/rfc4872>.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
              May 2007, <https://www.rfc-editor.org/info/rfc4873>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [G873.3]   International Telecommunication Union, "Optical transport
              network - Shared mesh protection", ITU-T Recommendation
              G.873.3, September 2017,
              <https://www.itu.int/rec/T-REC-G.873.3-201709-I/en>.

   [RFC6372]  Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              DOI 10.17487/RFC6372, September 2011,
              <https://www.rfc-editor.org/info/rfc6372>.

   [RFC7412]  Weingarten, Y., Aldrin, S., Pan, P., Ryoo, J., and G.
              Mirsky, "Requirements for MPLS Transport Profile (MPLS-TP)
              Shared Mesh Protection", RFC 7412, DOI 10.17487/RFC7412,
              December 2014, <https://www.rfc-editor.org/info/rfc7412>.

   [RFC8776]  Saad, T., Gandhi, R., Liu, X., Beeram, V., and I. Bryskin,
              "Common YANG Data Types for Traffic Engineering",
              RFC 8776, DOI 10.17487/RFC8776, June 2020,
              <https://www.rfc-editor.org/info/rfc8776>.

   [YANG-TE]  Saad, T., Gandhi, R., Liu, X., Beeram, V.P., Bryskin, I.,
              and O. Gonzalez de Dios, "A YANG Data Model for Traffic
              Engineering Tunnels, Label Switched Paths and Interfaces",
              Work in Progress, Internet-Draft, draft-ietf-teas-yang-te-
              30, 11 July 2022, <https://datatracker.ietf.org/doc/html/
              draft-ietf-teas-yang-te-30>.

Acknowledgements

   The authors would like to thank Adrian Farrel, Vishnu Pavan Beeram,
   Tom Petch, Ines Robles, John Scudder, Dale Worley, Dan Romascanu,
   Éric Vyncke, Roman Danyliw, Paul Wouters, Lars Eggert, Francesca
   Palombini, and Robert Wilton for their valuable comments and
   suggestions on this document.

Contributors

   The following person contributed significantly to the content of this
   document and should be considered a coauthor.

   Yuji Tochio
   Fujitsu
   Email: tochio@fujitsu.com


Authors' Addresses

   Jia He
   Huawei Technologies
   F3-1B, R&D Center, Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen
   China
   Email: hejia@huawei.com


   Italo Busi
   Huawei Technologies
   Email: italo.busi@huawei.com


   Jeong-dong Ryoo
   ETRI
   218 Gajeongno
   Yuseong-gu
   Daejeon
   34129
   South Korea
   Phone: +82-42-860-5384
   Email: ryoo@etri.re.kr


   Bin Yeong Yoon
   ETRI
   Email: byyun@etri.re.kr


   Peter Park
   KT
   Email: peter.park@kt.com