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

Abstract

  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
  https://www.rfc-editor.org/info/rfc9357.

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
  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 Revised BSD License text as described in Section 4.e of the
  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
    3.1.  The LSP-EXTENDED-FLAG TLV
    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
  Acknowledgements
  Contributors
  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",
  "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.

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.

3.1.  The LSP-EXTENDED-FLAG TLV

  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
  [PCEP-ENTROPY-LABEL].

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-
  FLAG TLV.

  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
  flags.

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
  [BIND-LABEL-SID].

  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,
             <https://www.rfc-editor.org/info/rfc2119>.

  [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>.

  [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,
             <https://www.rfc-editor.org/info/rfc8126>.

  [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,
             <https://www.rfc-editor.org/info/rfc8231>.

9.2.  Informative References

  [BIND-LABEL-SID]
             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,
             <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
             binding-label-sid-15>.

  [PCEP-ENTROPY-LABEL]
             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-
             pce-entropy-label-position-08>.

  [PCEPS-TLS1.3]
             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,
             <https://datatracker.ietf.org/doc/html/draft-dhody-pce-
             pceps-tls13-01>.

  [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,
             <https://www.rfc-editor.org/info/rfc8253>.

  [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>.

  [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,
             <https://www.rfc-editor.org/info/rfc8623>.

  [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.

Acknowledgements

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

Contributors

  The following people have substantially contributed to this document:

  Dhruv Dhody
  Huawei Technologies
  Email: [email protected]


  Greg Mirsky
  Ericsson
  Email: [email protected]


Author's Address

  Quan Xiong
  ZTE Corporation
  No.6 Huashi Park Rd
  Wuhan
  Hubei, 430223
  China
  Email: [email protected]

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