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IGP Extension for Path Computation Element Communication Protocol (PCEP) Security Capability Support in PCE Discovery (PCED)
RFC 9353

Document Type RFC - Proposed Standard (January 2023) IPR
Authors Diego Lopez , Qin Wu , Dhruv Dhody , Qiufang Ma , Daniel King
Last updated 2023-01-13
Replaces draft-wu-lsr-pce-discovery-security-support
RFC stream Internet Engineering Task Force (IETF)
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Reviews
OPSDIR Telechat Review Incomplete, due 2022-10-04
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Acee Lindem
Shepherd write-up Show Last changed 2022-10-10
IESG IESG state RFC 9353 (Proposed Standard)
Action Holders
(None)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD John Scudder
Send notices to Acee Lindem <acee@cisco.com>, pce@ietf.org, lsr@ietf.org
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
RFC 9353


Internet Engineering Task Force (IETF)                          D. Lopez
Request for Comments: 9353                                Telefonica I+D
Updates: 5088, 5089, 8231, 8306                                    Q. Wu
Category: Standards Track                                       D. Dhody
ISSN: 2070-1721                                                    Q. Ma
                                                                  Huawei
                                                                 D. King
                                                      Old Dog Consulting
                                                            January 2023

IGP Extension for Path Computation Element Communication Protocol (PCEP)
          Security Capability Support in PCE Discovery (PCED)

Abstract

   When a Path Computation Element (PCE) is a Label Switching Router
   (LSR) or a server participating in the Interior Gateway Protocol
   (IGP), its presence and path computation capabilities can be
   advertised using IGP flooding.  The IGP extensions for PCE Discovery
   (PCED) (RFCs 5088 and 5089) define a method to advertise path
   computation capabilities using IGP flooding for OSPF and IS-IS,
   respectively.  However, these specifications lack a method to
   advertise Path Computation Element Communication Protocol (PCEP)
   security (e.g., Transport Layer Security (TLS) and TCP Authentication
   Option (TCP-AO)) support capability.

   This document defines capability flag bits for the PCE-CAP-FLAGS sub-
   TLV that can be announced as an attribute in the IGP advertisement to
   distribute PCEP security support information.  In addition, this
   document updates RFCs 5088 and 5089 to allow advertisement of a Key
   ID or KEY-CHAIN-NAME sub-TLV to support TCP-AO security capability.
   This document also updates RFCs 8231 and 8306.

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/rfc9353.

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
   3.  IGP Extension for PCEP Security Capability Support
     3.1.  Use of PCEP Security Capability Support for PCED
     3.2.  KEY-ID Sub-TLV
       3.2.1.  IS-IS
       3.2.2.  OSPF
     3.3.  KEY-CHAIN-NAME Sub-TLV
       3.3.1.  IS-IS
       3.3.2.  OSPF
   4.  Updates to RFCs
   5.  Backward Compatibility Considerations
   6.  Management Considerations
     6.1.  Control of Policy and Functions
     6.2.  Information and Data Model
     6.3.  Liveness Detection and Monitoring
     6.4.  Verification of Correct Operations
     6.5.  Requirements on Other Protocols and Functional Components
     6.6.  Impact on Network Operations
   7.  Security Considerations
   8.  IANA Considerations
     8.1.  PCE Capability Flags
     8.2.  PCED Sub-TLV Type Indicators
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   As described in [RFC5440], privacy and integrity are important issues
   for communication using the Path Computation Element Communication
   Protocol (PCEP); an attacker that intercepts a PCEP message could
   obtain sensitive information related to computed paths and resources.
   Authentication and integrity checks allow the receiver of a PCEP
   message to know that the message genuinely comes from the node that
   purports to have sent it and whether the message has been modified.

   Among the possible solutions mentioned in [RFC5440], Transport Layer
   Security (TLS) [RFC8446] provides support for peer authentication,
   message encryption, and integrity while TCP-AO) [RFC5925] and
   Cryptographic Algorithms for TCP-AO [RFC5926] offer significantly
   improved security for applications using TCP.  As specified in
   Section 4 of [RFC8253], the PCC needs to know whether the PCE server
   supports TLS or TCP-AO as a secure transport in order for a Path
   Computation Client (PCC) to establish a connection with a PCE server
   using TLS or TCP-AO.

   [RFC5088] and [RFC5089] define a method to advertise path computation
   capabilities using IGP flooding for OSPF and IS-IS, respectively.
   However, these specifications lack a method to advertise PCEP
   security (e.g., TLS and TCP-AO) support capability.

   This document defines capability flag bits for the PCE-CAP-FLAGS sub-
   TLV that can be announced as attributes in the IGP advertisement to
   distribute PCEP security support information.  In addition, this
   document updates [RFC5088] and [RFC5089] to allow advertisement of a
   KeyID or KEY-CHAIN-NAME sub-TLV to support TCP-AO security
   capability.

   IANA created a top-level registry titled "Path Computation Element
   (PCE) Capability Flags" per [RFC5088].  This document updates
   [RFC5088] and moves it to follow the heading of the "Interior Gateway
   Protocol (IGP) Parameters" registry.  [RFC5089] states that the IS-IS
   PCE-CAP-FLAGS sub-TLV uses the same registry as OSPF.  This document
   updates [RFC5089] to refer to the new IGP registry.  Further, this
   document updates [RFC8231] where it references the registry location
   as the "Open Shortest Path First v2 (OSPFv2) Parameters" registry to
   the "Interior Gateway Protocol (IGP) Parameters" registry.  This
   document also updates [RFC8306] by changing the term "OSPF PCE
   Capability Flag" to read as "Path Computation Element (PCE)
   Capability Flags" and to note the corresponding registry now exists
   in the "Interior Gateway Protocol (IGP) Parameters" registry.

      |  Note that [RFC5557] uses the term "OSPF registry" instead of
      |  the "IGP registry", whereas [RFC8623] and [RFC9168] use the
      |  term "OSPF Parameters" instead of "IGP Parameters".

      |  Note that the PCEP Open message exchange is another way to
      |  discover PCE capabilities information; however, in this
      |  instance, the TCP-security-related key parameters need to be
      |  known before the PCEP session is established and the PCEP Open
      |  messages are exchanged.  Thus, the IGP advertisement and
      |  flooding mechanisms need to be leveraged for PCE discovery and
      |  capabilities advertisement.

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.

3.  IGP Extension for PCEP Security Capability Support

   [RFC5088] defines a PCE Discovery (PCED) TLV carried in an OSPF
   Router Information Link State Advertisement (LSA) as defined in
   [RFC7770] to facilitate PCED using OSPF.  This document defines two
   capability flag bits in the OSPF PCE Capability Flags to indicate
   TCP-AO support [RFC5925] [RFC5926] and PCEP over TLS support
   [RFC8253], respectively.

   Similarly, [RFC5089] defines the PCED sub-TLV for use in PCED using
   IS-IS.  This document will use the same flag for the OSPF PCE
   Capability Flags sub-TLV to allow IS-IS to indicate TCP-AO support
   and PCEP over TLS support, respectively.

   The IANA assignments for shared OSPF and IS-IS Security Capability
   Flags are documented in Section 8.1 of this document.

3.1.  Use of PCEP Security Capability Support for PCED

   TCP-AO and PCEP over TLS support flag bits are advertised using IGP
   flooding.

   *  PCE supports TCP-AO: IGP advertisement SHOULD include a TCP-AO
      support flag bit.

   *  PCE supports TLS: IGP advertisement SHOULD include PCEP over TLS
      support flag bit.

   If the PCE supports multiple security mechanisms, it SHOULD include
   all corresponding flag bits in its IGP advertisement.

   A client's configuration MAY indicate that support for a given
   security capability is required.  If a client is configured to
   require that its PCE server supports TCP-AO, the client MUST verify
   that the TCP-AO flag bit in the PCE-CAP-FLAGS sub-TLV for a given
   server is set before it opens a connection to that server.
   Similarly, if the client is configured to require that its PCE server
   supports TLS, the client MUST verify that the PCEP over TLS support
   flag bit in the PCE-CAP-FLAGS sub-TLV for a given server is set
   before it opens a connection to that server.

3.2.  KEY-ID Sub-TLV

   The KEY-ID sub-TLV specifies an identifier that can be used by the
   PCC to identify the TCP-AO key (referred to as "KeyID" in [RFC5925]).

3.2.1.  IS-IS

   The KEY-ID sub-TLV MAY be present in the PCED sub-TLV carried within
   the IS-IS Router CAPABILITY TLV when the capability flag bit of the
   PCE-CAP-FLAGS sub-TLV in IS-IS is set to indicate TCP-AO support.

   The KEY-ID sub-TLV has the following format:

   Type:  6

   Length:  1

   KeyID:  The one-octet KeyID as per [RFC5925] to uniquely identify the
      Master Key Tuple (MKT).

3.2.2.  OSPF

   Similarly, this sub-TLV MAY be present in the PCED TLV carried within
   the OSPF Router Information LSA when the capability flag bit of the
   PCE-CAP-FLAGS sub-TLV in OSPF is set to indicate TCP-AO support.

   The format of the KEY-ID sub-TLV is as follows:

                        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 = 6         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    KeyID      |                 Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  6

   Length:  4

   KeyID:  The one octet KeyID as per [RFC5925] to uniquely identify the
      MKT.

   Reserved:  MUST be set to zero while sending and ignored on receipt.

3.3.  KEY-CHAIN-NAME Sub-TLV

   The KEY-CHAIN-NAME sub-TLV specifies a key chain name that can be
   used by the PCC to identify the key chain.  The key chain name could
   be manually configured via command-line interface (CLI) or installed
   in the YANG datastore (see [RFC8177]) at the PCC.

3.3.1.  IS-IS

   The KEY-CHAIN-NAME sub-TLV MAY be present in the PCED sub-TLV carried
   within the IS-IS Router CAPABILITY TLV when the capability flag bit
   of the PCE-CAP-FLAGS sub-TLV in IS-IS is set to indicate TCP-AO
   support.

   The KEY-CHAIN-NAME sub-TLV has the following format:

   Type:  7

   Length:  Variable, encodes the length of the value field.

   Key Chain Name:  The Key Chain Name contains a string of 1 to 255
      octets to be used to identify the key chain.  It MUST be encoded
      using UTF-8.  A receiving entity MUST NOT interpret invalid UTF-8
      sequences and ignore them.  This field is not NULL terminated.
      UTF-8 "Shortest Form" encoding is REQUIRED to guard against the
      technical issues outlined in [UTR36].

3.3.2.  OSPF

   Similarly, this sub-TLV MAY be present in the PCED TLV carried within
   the OSPF Router Information LSA when the capability flag bit of the
   PCE-CAP-FLAGS sub-TLV in OSPF is set to indicate TCP-AO support.  The
   sub-TLV MUST be zero-padded so that the sub-TLV is 4-octet aligned.

   The format of KEY-CHAIN-NAME sub-TLV is as follows:

                        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 = 7         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Key Chain Name                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  7

   Length:  Variable, padding is not included in the Length field.

   Key Chain Name:  The Key Chain Name contains a string of 1 to 255
      octets to be used to identify the key chain.  It MUST be encoded
      using UTF-8.  A receiving entity MUST NOT interpret invalid UTF-8
      sequences and ignore them.  This field is not NULL terminated.
      UTF-8 "Shortest Form" encoding is REQUIRED to guard against the
      technical issues outlined in [UTR36].  The sub-TLV MUST be zero-
      padded so that the sub-TLV is 4-octet aligned.

4.  Updates to RFCs

   Section 4 of [RFC5088] states that no new sub-TLVs will be added to
   the PCED TLV and no new PCE information will be carried in the Router
   Information LSA.  This document updates [RFC5088] by allowing the two
   sub-TLVs defined in this document to be carried in the PCED TLV
   advertised in the Router Information LSA.

   Section 4 of [RFC5089] states that no new sub-TLVs will be added to
   the PCED TLV and no new PCE information will be carried in the Router
   CAPABILITY TLV.  This document updates [RFC5089] by allowing the two
   sub-TLVs defined in this document to be carried in the PCED TLV
   advertised in the Router CAPABILITY TLV.

   This introduction of additional sub-TLVs should be viewed as an
   exception to the policies in [RFC5088] and [RFC5089], which is
   justified by the requirement to discover the PCEP security support
   prior to establishing a PCEP session.  The restrictions defined in
   [RFC5088] and [RFC5089] should still be considered to be in place.
   If new advertisements are required in the future, alternative
   mechanisms such as using [RFC6823] or [LSR-OSPF-TRANSPORT-INSTANCE]
   should be considered.

   The registry for the PCE Capability Flags assigned in Section 8.3 of
   [RFC5557], Section 8.1 of [RFC8231], Section 6.9 of [RFC8306],
   Section 11.1 of [RFC8623], and Section 10.5 of [RFC9168] has changed
   to the IGP Parameters "Path Computation Element (PCE) Capability
   Flags" registry created in this document.

5.  Backward Compatibility Considerations

   An LSR that does not support the IGP PCE capability bits specified in
   this document silently ignores those bits.

   An LSR that does not support the KEY-ID and KEY-CHAIN-NAME sub-TLVs
   specified in this document silently ignores those sub-TLVs.

   IGP extensions defined in this document do not introduce any new
   interoperability issues.

6.  Management Considerations

   Manageability considerations for PCED are addressed in Section 4.10
   of [RFC4674], Section 9 of [RFC5088], and Section 9 of [RFC5089].

6.1.  Control of Policy and Functions

   A PCE implementation SHOULD allow the following parameters to be
   configured on the PCE:

   *  support for TCP-AO

   *  the KeyID used by TCP-AO

   *  Key Chain Name

   *  support for TLS

6.2.  Information and Data Model

   The YANG module for PCEP [PCE-PCEP-YANG] supports PCEP security
   parameters (key, key chain, and TLS).

6.3.  Liveness Detection and Monitoring

   Normal operations of the IGP meet the requirements for liveness
   detection and monitoring.

6.4.  Verification of Correct Operations

   The correlation of PCEP security information advertised against
   information received can be achieved by comparing the information in
   the PCED sub-TLV received by the PCC with that stored at the PCE
   using the PCEP YANG.

6.5.  Requirements on Other Protocols and Functional Components

   There are no new requirements on other protocols.

6.6.  Impact on Network Operations

   Frequent changes in PCEP security information advertised in the PCED
   sub-TLV may have a significant impact on IGP and might destabilize
   the operation of the network by causing the PCCs to reconnect
   sessions with PCEs.  Section 4.10.4 of [RFC4674], Section 9.6 of
   [RFC5088], and Section 9.6 of [RFC5089] list techniques that are
   applicable to this document as well.

7.  Security Considerations

   Security considerations as specified by [RFC5088] and [RFC5089] are
   applicable to this document.

   As described in Section 10.2 of [RFC5440], a PCEP speaker MUST
   support TCP MD5 [RFC2385], so no capability advertisement is needed
   to indicate support.  However, as noted in [RFC6952], TCP MD5 has
   been obsoleted by TCP-AO [RFC5925] because of security concerns.
   TCP-AO is not widely implemented; therefore, it is RECOMMENDED that
   PCEP be secured using TLS per [RFC8253] (which updates [RFC5440]).
   An implementation SHOULD offer at least one of the two security
   capabilities defined in this document.

   The information related to PCEP security is sensitive and due care
   needs to be taken by the operator.  This document defines new
   capability bits that are susceptible to a downgrade attack by setting
   them to zero.  The content of the Key-ID or KEY-CHAIN-NAME sub-TLV
   can be altered to enable an on-path attack.  Thus, before advertising
   the PCEP security parameters by using the mechanism described in this
   document, the IGP MUST be known to provide authentication and
   integrity for the PCED TLV using the mechanisms defined in [RFC5304],
   [RFC5310], or [RFC5709].

   Moreover, as stated in the security considerations of [RFC5088] and
   [RFC5089], there are no mechanisms defined in OSPF or IS-IS to
   protect the confidentiality of the PCED TLV.  For this reason, the
   operator must ensure that no private data is carried in the TLV.  For
   example, the operator must ensure that KeyIDs or key chain names do
   not reveal sensitive information about the network.

8.  IANA Considerations

8.1.  PCE Capability Flags

   IANA has moved the "Path Computation Element (PCE) Capability Flags"
   registry from the "Open Shortest Path First v2 (OSPFv2) Parameters"
   grouping to the "Interior Gateway Protocol (IGP) Parameters"
   grouping.

   IANA has made the following additional assignments from the "Path
   Computation Element (PCE) Capability Flags" registry:

               +=====+========================+===========+
               | Bit | Capability Description | Reference |
               +=====+========================+===========+
               | 17  | TCP-AO Support         | RFC 9353  |
               +-----+------------------------+-----------+
               | 18  | PCEP over TLS support  | RFC 9353  |
               +-----+------------------------+-----------+

                 Table 1: Path Computation Element (PCE)
                      Capability Flags Registrations

   The grouping is located at: <https://www.iana.org/assignments/igp-
   parameters/>.

8.2.  PCED Sub-TLV Type Indicators

   The PCED sub-TLVs are defined in [RFC5088] and [RFC5089], but a
   corresponding IANA registry was not created.  IANA has created a new
   registry called "PCE Discovery (PCED) Sub-TLV Type Indicators" under
   the "Interior Gateway Protocol (IGP) Parameters" registry.  The
   registration policy for this registry is "Standards Action"
   [RFC8126].  Values in this registry come from the range 0-65535.

   This registry is initially populated as follows:

             +=======+=================+====================+
             | Value | Description     | Reference          |
             +=======+=================+====================+
             | 0     | Reserved        | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 1     | PCE-ADDRESS     | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 2     | PATH-SCOPE      | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 3     | PCE-DOMAIN      | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 4     | NEIG-PCE-DOMAIN | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 5     | PCE-CAP-FLAGS   | RFC 9353, RFC 5088 |
             +-------+-----------------+--------------------+
             | 6     | KEY-ID          | RFC 9353           |
             +-------+-----------------+--------------------+
             | 7     | KEY-CHAIN-NAME  | RFC 9353           |
             +-------+-----------------+--------------------+

                Table 2: Initial Contents of the PCED Sub-
                       TLV Type Indicators Registry

   This registry is used by both the OSPF PCED TLV and the IS-IS PCED
   sub-TLV.

   This grouping is located at: <https://www.iana.org/assignments/igp-
   parameters/>.

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>.

   [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>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <https://www.rfc-editor.org/info/rfc5304>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC5557]  Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
              Computation Element Communication Protocol (PCEP)
              Requirements and Protocol Extensions in Support of Global
              Concurrent Optimization", RFC 5557, DOI 10.17487/RFC5557,
              July 2009, <https://www.rfc-editor.org/info/rfc5557>.

   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, DOI 10.17487/RFC5709, October
              2009, <https://www.rfc-editor.org/info/rfc5709>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.

   [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>.

   [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>.

   [RFC8306]  Zhao, Q., Dhody, D., Ed., Palleti, R., and D. King,
              "Extensions to the Path Computation Element Communication
              Protocol (PCEP) for Point-to-Multipoint Traffic
              Engineering Label Switched Paths", RFC 8306,
              DOI 10.17487/RFC8306, November 2017,
              <https://www.rfc-editor.org/info/rfc8306>.

   [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>.

   [RFC9168]  Dhody, D., Farrel, A., and Z. Li, "Path Computation
              Element Communication Protocol (PCEP) Extension for Flow
              Specification", RFC 9168, DOI 10.17487/RFC9168, January
              2022, <https://www.rfc-editor.org/info/rfc9168>.

9.2.  Informative References

   [LSR-OSPF-TRANSPORT-INSTANCE]
              Lindem, A., Qu, Y., Roy, A., and S. Mirtorabi, "OSPF-GT
              (Generalized Transport)", Work in Progress, Internet-
              Draft, draft-ietf-lsr-ospf-transport-instance-04, 3
              January 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-lsr-ospf-transport-instance-04>.

   [PCE-PCEP-YANG]
              Dhody, D., Ed., Beeram, V., Hardwick, J., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-20, 23 October
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-pcep-yang-20>.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC4674]  Le Roux, J.L., Ed., "Requirements for Path Computation
              Element (PCE) Discovery", RFC 4674, DOI 10.17487/RFC4674,
              October 2006, <https://www.rfc-editor.org/info/rfc4674>.

   [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>.

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,
              <https://www.rfc-editor.org/info/rfc5926>.

   [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", RFC 6823,
              DOI 10.17487/RFC6823, December 2012,
              <https://www.rfc-editor.org/info/rfc6823>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [UTR36]    Davis, M., Ed. and M. Suignard, Ed., "Unicode Security
              Considerations", Unicode Technical Report #36, August
              2010, <https://www.unicode.org/unicode/reports/tr36/>.

Acknowledgments

   The authors of this document would like to thank Acee Lindem, Julien
   Meuric, Les Ginsberg, Ketan Talaulikar, Tom Petch, Aijun Wang, and
   Adrian Farrel for the review and comments.

   The authors would also like to give special thanks to Michale Wang
   for his major contributions to the initial draft version.

   Thanks to John Scudder for providing an excellent AD review.  Thanks
   to Carlos Pignataro, Yaron Sheffer, Ron Bonica, and Will (Shucheng)
   LIU for directorate reviews.

   Thanks to Lars Eggert, Robert Wilton, Roman Danyliw, Éric Vyncke,
   Paul Wouters, Murray Kucherawy, and Warren Kumari for IESG reviews.

Authors' Addresses

   Diego R. Lopez
   Telefonica I+D
   Spain
   Email: diego.r.lopez@telefonica.com

   Qin Wu
   Huawei Technologies
   Yuhua District
   101 Software Avenue
   Nanjing
   Jiangsu, 210012
   China
   Email: bill.wu@huawei.com

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore 560037
   Karnataka
   India
   Email: dhruv.ietf@gmail.com

   Qiufang Ma
   Huawei Technologies
   Yuhua District
   101 Software Avenue
   Nanjing
   Jiangsu, 210012
   China
   Email: maqiufang1@huawei.com

   Daniel King
   Old Dog Consulting
   United Kingdom
   Email: daniel@olddog.co.uk