RFC 9357

Internet Engineering Task Force (IETF)                          Q. Xiong
Request for Comments: 9357                               ZTE Corporation
Category: Standards Track                                  February 2023
ISSN: 2070-1721

    Label Switched Path (LSP) Object Flag Extension for Stateful PCE


   RFC 8231 describes a set of extensions to the Path Computation
   Element Communication Protocol (PCEP) to enable stateful control of
   MPLS-TE and GMPLS Label Switched Paths (LSPs) via PCEP.  One of the
   extensions is the LSP object, which includes a Flag field with a
   length of 12 bits.  However, all bits of the Flag field have already
   been assigned.

   This document defines a new LSP-EXTENDED-FLAG TLV for the LSP object
   for an extended Flag field.

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

Copyright Notice

   Copyright (c) 2023 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
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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in this Document
     2.1.  Terminology
     2.2.  Requirements Language
   3.  PCEP Extension
     3.2.  Processing
   4.  Advice for Specification of New Flags
   5.  Backward Compatibility
   6.  IANA Considerations
     6.1.  LSP Object
       6.1.1.  PCEP TLV Type Indicators
       6.1.2.  LSP Extended Flags Field
   7.  Management Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Appendix A.  Working Group Discussion

   Author's Address

1.  Introduction

   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP), which is used between a PCE and a Path Computation
   Client (PCC) (or other PCE) to enable computation of Multi-protocol
   Label Switching for Traffic Engineering (MPLS-TE) Label Switched
   Paths (LSPs).

   PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
   of extensions to PCEP to enable active control of MPLS-TE and
   Generalized MPLS (GMPLS) tunnels.  One of the extensions is the LSP
   object, which contains a Flag field; bits in the Flag field are used
   to indicate delegation, synchronization, removal, etc.

   As defined in [RFC8231], the length of the Flag field is 12 bits, and
   all of the bits have already been defined as shown in Table 1.  This
   document extends the Flag field of the LSP object for other use by
   defining a new LSP-EXTENDED-FLAG TLV for an extended Flag field in
   the LSP object (see Section 3.1).

             | Bit | Description          | Reference        |
             | 0   | PCE-allocation       | [BIND-LABEL-SID] |
             | 1   | ERO-compression      | [RFC8623]        |
             | 2   | Fragmentation        | [RFC8623]        |
             | 3   | P2MP                 | [RFC8623]        |
             | 4   | Create               | [RFC8281]        |
             | 5-7 | Operational (3 bits) | [RFC8281]        |
             | 8   | Administrative       | [RFC8281]        |
             | 9   | Remove               | [RFC8281]        |
             | 10  | SYNC                 | [RFC8281]        |
             | 11  | Delegate             | [RFC8281]        |

                       Table 1: LSP Object Flag Field

2.  Conventions Used in this Document

2.1.  Terminology

   The terminology is defined in [RFC5440] and [RFC8231].

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

3.  PCEP Extension

   The LSP object is defined in Section 7.3 of [RFC8231].  This document
   defines a new LSP-EXTENDED-FLAG TLV for an extended Flag field in the
   LSP object.


   The format of the LSP-EXTENDED-FLAG TLV shown in Figure 1 follows the
   format of all PCEP TLVs, as defined in [RFC5440].

      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
     |           Type=64             |           Length              |
     |                                                               |
     //                 LSP Extended Flags                          //
     |                                                               |

                   Figure 1: LSP-EXTENDED-FLAG TLV Format

   Type (16 bits):  64

   Length (16 bits):  This indicates the length of the value portion in
      bytes.  It MUST be in multiples of 4 and greater than 0.

   LSP Extended Flags:  This contains an array of units of 32-bit flags
      numbered from the most significant as bit zero, where each bit
      represents one LSP flag (for operation, feature, or state).  The
      LSP Extended Flags field SHOULD use the minimal amount of space
      needed to encode the flag bits.  Currently, no bits are assigned.
      Unassigned bits MUST be set to zero on transmission and MUST be
      ignored on receipt.

   As an example of usage of the LSP-EXTENDED-FLAG TLV, the E-flag is
   requested for entropy label configuration, as proposed in

3.2.  Processing

   The LSP Extended Flags field is an array of units of 32 flags that
   are allocated starting from the most significant bit.  The bits of
   the LSP Extended Flags field will be assigned by future documents.
   This document does not define any flags.  Flags that an
   implementation is not supporting MUST be set to zero on transmission.
   Implementations that do not understand any particular flag MUST
   ignore the flag.

   Note that PCEP peers MUST handle varying lengths of the LSP-EXTENDED-

   If a PCEP speaker receives the LSP-EXTENDED-FLAG TLV of a length more
   than it currently supports or understands, it MUST ignore the bits
   beyond that length.

   If a PCEP speaker receives the LSP-EXTENDED-FLAG TLV of a length less
   than the one supported by the implementation, it MUST act as if the
   bits beyond the length were not set.

4.  Advice for Specification of New Flags

   Following the model provided in Section 3.1 of [RFC8786], we provide
   the following advice for new specifications that define additional
   flags.  Each such specification is expected to describe the
   interaction between these new flags and any existing flags.  In
   particular, new specifications are expected to explain how to handle
   the cases when both new and preexisting flags are set.  They are also
   expected to discuss any security implications of the additional flags
   (if any) and their interactions with existing flags.

5.  Backward Compatibility

   The LSP-EXTENDED-FLAG TLV defined in this document does not introduce
   any backward compatibility issues.  An implementation that does not
   understand or support the LSP-EXTENDED-FLAG TLV MUST ignore the TLV,
   as per [RFC5440].  Future documents that define bits in the LSP-
   EXTENDED-FLAG TLV are expected to also define the error handling
   required for cases in which the LSP-EXTENDED-FLAG TLV is missing when
   it MUST be present.

   Further, any additional bits in the LSP-EXTENDED-FLAG TLV that are
   not understood by an implementation MUST be ignored.  It is expected
   that future documents that define bits in the LSP-EXTENDED-FLAG TLV
   will take that into consideration.

6.  IANA Considerations

6.1.  LSP Object

6.1.1.  PCEP TLV Type Indicators

   IANA has allocated the following TLV Type Indicator value within the
   "PCEP TLV Type Indicators" registry of the "Path Computation Element
   Protocol (PCEP) Numbers" registry:

                 | Value | Description       | Reference |
                 | 64    | LSP-EXTENDED-FLAG | RFC 9357  |

                                  Table 2

6.1.2.  LSP Extended Flags Field

   IANA has created the "LSP-EXTENDED-FLAG TLV Flag Field" registry
   within the "Path Computation Element Protocol (PCEP) Numbers"
   registry to manage the LSP Extended Flags field of the LSP-EXTENDED-
   FLAG TLV.  New values are assigned by Standards Action [RFC8126].
   Each bit should be tracked with the following qualities:

   *  Bit number (counting from bit 0 as the most significant bit)

   *  Capability Description

   *  Reference

   No values are currently defined.  Bits 0-31 are initially marked as
   "Unassigned".  Bits with a higher ordinal than 31 will be added to
   the registry in future documents if necessary.

7.  Management Considerations

   Implementations receiving set LSP Extended Flags that they do not
   recognize MAY log this.  That could be helpful for diagnosing
   backward compatibility issues with future features that utilize those

8.  Security Considerations

   [RFC8231] sets out security considerations for PCEP when used for
   communication with a stateful PCE.  This document does not change
   those considerations.  For LSP object processing, see [RFC8231].

   The flags for the LSP object and their associated security
   considerations are specified in [RFC8231], [RFC8281], [RFC8623], and

   This document provides for the future addition of flags in the LSP
   object.  Any future document that specifies new flags must also
   discuss any associated security implications.  No additional security
   issues are raised in this document beyond those that exist in the
   referenced documents.  Note that [RFC8231] recommends that the
   stateful PCEP extension be authenticated and encrypted using
   Transport Layer Security (TLS) [RFC8253] [PCEPS-TLS1.3], as per the
   recommendations and best current practices in [RFC9325].  Assuming
   that the recommendation is followed, then the flags will be protected
   by TLS.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

   [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>.

   [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,

9.2.  Informative References

              Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
              and C. Li, Ed., "Carrying Binding Label/Segment Identifier
              (SID) in PCE-based Networks.", Work in Progress, Internet-
              Draft, draft-ietf-pce-binding-label-sid-15, 20 March 2022,

              Xiong, Q., Peng, S., and F. Qin, "PCEP Extension for SR-
              MPLS Entropy Label Position", Work in Progress, Internet-
              Draft, draft-peng-pce-entropy-label-position-08, 29 August
              2022, <https://datatracker.ietf.org/doc/html/draft-peng-

              Dhody, D., Turner, S., and R. Housley, "PCEPS with TLS
              1.3", Work in Progress, Internet-Draft, draft-dhody-pce-
              pceps-tls13-01, 20 October 2022,

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,

   [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,

   [RFC8623]  Palle, U., Dhody, D., Tanaka, Y., and V. Beeram, "Stateful
              Path Computation Element (PCE) Protocol Extensions for
              Usage with Point-to-Multipoint TE Label Switched Paths
              (LSPs)", RFC 8623, DOI 10.17487/RFC8623, June 2019,

   [RFC8786]  Farrel, A., "Updated Rules for Processing Stateful PCE
              Request Parameters Flags", RFC 8786, DOI 10.17487/RFC8786,
              May 2020, <https://www.rfc-editor.org/info/rfc8786>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.

Appendix A.  Working Group Discussion

   The working group discussed the idea of a fixed length (with 32 bits)
   for the LSP-EXTENDED-FLAG TLV.  Though 32 bits would be sufficient
   for quite a while, the use of variable length with a multiple of 32
   bits allows for future extensibility where we would never run out of
   flags and there would not be a need to define yet another TLV in the
   future.  Further, note that [RFC5088] and [RFC5089] use the same
   approach for the PCE-CAP-FLAGS sub-TLV and are found to be useful.


   The authors would like to thank Loa Andersson, Adrian Farrel, Aijun
   Wang, and Gyan Mishra for their reviews, suggestions, and comments
   for this document.


   The following people have substantially contributed to this document:

   Dhruv Dhody
   Huawei Technologies
   Email: dhruv.ietf@gmail.com

   Greg Mirsky
   Email: gregimirsky@gmail.com

Author's Address

   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Hubei, 430223
   Email: xiong.quan@zte.com.cn