Internet DRAFT - draft-ietf-pce-segment-routing-policy-cp

draft-ietf-pce-segment-routing-policy-cp







PCE Working Group                                           M. Koldychev
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                            S. Sivabalan
Expires: 12 August 2024                                Ciena Corporation
                                                                C. Barth
                                                  Juniper Networks, Inc.
                                                                 S. Peng
                                                     Huawei Technologies
                                                              H. Bidgoli
                                                                   Nokia
                                                         9 February 2024


             PCEP Extensions for SR Policy Candidate Paths
              draft-ietf-pce-segment-routing-policy-cp-14

Abstract

   A Segment Routing (SR) Policy is a non-empty set of SR Candidate
   Paths, which share the same <headend, color, endpoint> tuple.  SR
   Policy is modeled in PCEP as an Association of one or more SR
   Candidate Paths.  PCEP extensions are defined to signal additional
   attributes of an SR Policy.  The mechanism is applicable to all SR
   forwarding planes (MPLS, SRv6, etc.).

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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on 12 August 2024.

Copyright Notice

   Copyright (c) 2024 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  SR Policy Identifier  . . . . . . . . . . . . . . . . . .   4
     3.2.  SR Policy Candidate Path Identifier . . . . . . . . . . .   4
     3.3.  SR Policy Candidate Path Attributes . . . . . . . . . . .   4
   4.  SR Policy Association . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Association Parameters  . . . . . . . . . . . . . . . . .   5
     4.2.  Association Information . . . . . . . . . . . . . . . . .   7
       4.2.1.  SR Policy Name TLV  . . . . . . . . . . . . . . . . .   7
       4.2.2.  SR Policy Candidate Path Identifier TLV . . . . . . .   8
       4.2.3.  SR Policy Candidate Path Name TLV . . . . . . . . . .   9
       4.2.4.  SR Policy Candidate Path Preference TLV . . . . . . .  10
   5.  Other Mechanisms  . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  SR Policy Capability TLV  . . . . . . . . . . . . . . . .  10
     5.2.  Computation Priority TLV  . . . . . . . . . . . . . . . .  11
     5.3.  Explicit Null Label Policy (ENLP) TLV . . . . . . . . . .  12
     5.4.  Invalidation TLV  . . . . . . . . . . . . . . . . . . . .  13
     5.5.  Specified-BSID-only . . . . . . . . . . . . . . . . . . .  14
     5.6.  Stateless Operation . . . . . . . . . . . . . . . . . . .  15
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  15
     6.2.  PCEP TLV Type Indicators  . . . . . . . . . . . . . . . .  16
     6.3.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .  16
     6.4.  TE-PATH-BINDING TLV Flag field  . . . . . . . . . . . . .  17
     6.5.  SR Policy Candidate Path Protocol Origin field  . . . . .  17
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Cisco . . . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.2.  Juniper . . . . . . . . . . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19



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   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  20
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     10.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   [RFC8664] specifies extensions that allow PCEP to work with basic SR-
   TE paths.  [RFC8697] introduces a generic mechanism to create a
   grouping of LSPs, called an Association.  [RFC9256] introduces the SR
   Policy construct as a grouping of SR Candidate Paths.

   This document extends [RFC8664] to support signaling SR Policy
   Candidate Paths and their attributes.  SR Policy is modeled in PCEP
   as an Association, where the SR Candidate Paths are the members of
   that Association.  Thus the PCE can take computation and control
   decisions about the Candidate Paths, with the additional knowledge
   that these Candidate Paths belong to the same SR Policy.

2.  Terminology

   The following terminologies are used in this document:

   Endpoint:  The IPv4 or IPv6 endpoint address of the SR Policy in
      question, as described in [RFC9256].

   SRPA:  SR Policy Association.  PCEP ASSOCATION that describes the SR
      Policy.  Depending on discussion context, it refers to a PCEP
      object or to a group of LSPs that belong to the Association.

   Association Parameters:  As described in [RFC8697], refers to the key
      data, that uniquely identifies the Association in the network.

   Association Information:  As described in [RFC8697], refers to the
      non-key information about the Association.

3.  Overview

   The SR Policy is represented by a new type of PCEP Association,
   called the SR Policy Association (SRPA).  The SR Candidate Paths of
   an SR Policy are the PCEP LSPs within the same SRPA.  The subject of
   encoding multiple Segment Lists within an SR Policy Candidate Path is
   described in [I-D.ietf-pce-multipath].






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   The SRPA carries three pieces of information: SR Policy Identifier,
   SR Policy Candidate Path Identifier, and SR Policy Candidate Path
   Attribute(s).

   Additional information is also carried outside of SRPA: Computation
   Priority, Explicit Null Label Policy, Drop upon Invalid behavior, and
   Specified-BSID-only.

3.1.  SR Policy Identifier

   SR Policy Identifier uniquely identifies the SR Policy within the
   network.  SR Policy Identifier MUST be the same for all SR Policy
   Candidate Paths in the same SRPA.  SR Policy Identifier MUST NOT
   change for a given SR Policy Candidate Path during its lifetime.  SR
   Policy Identifier MUST be different for different SRPAs.  SR Policy
   Identifier consist of:

   *  Headend router where the SR Policy originates.

   *  Color of SR Policy.

   *  Endpoint of SR Policy.

3.2.  SR Policy Candidate Path Identifier

   SR Policy Candidate Path Identifier uniquely identifies the SR Policy
   Candidate Path within the context of an SR Policy.  SR Policy
   Candidate Path Identifier MUST NOT change for a given LSP during its
   lifetime.  SR Policy Candidate Path Identifier MUST be different for
   distinct Candidate Paths within the same SRPA.  When these rules are
   not satisfied, the PCEP speaker MUST send a PCErr message with Error-
   Type = 26 "Association Error", Error Value = TBD8 "SR Policy
   Candidate Path Identifier Mismatch".  SR Policy Candidate Path
   Identifier consist of:

   *  Protocol Origin.

   *  Originator.

   *  Discriminator.

3.3.  SR Policy Candidate Path Attributes

   SR Policy Candidate Path Attributes carry non-key information about
   the Candidate Path and MAY change during the lifetime of the LSP.  SR
   Policy Candidate Path Attributes consist of:

   *  Preference.



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   *  Optionally, the SR Policy Candidate Path name.

   *  Optionally, the SR Policy name.

4.  SR Policy Association

   Two ASSOCIATION object types for IPv4 and IPv6 are defined in
   [RFC8697].  The ASSOCIATION object includes "Association Type"
   indicating the type of the association group.  This document adds a
   new Association Type (6) "SR Policy Association".

   This Association Type is dynamic in nature, thus operator-configured
   Association Range MUST NOT be set for this Association type and MUST
   be ignored.

   A PCEP speaker that supports the SRPA MUST send the ASSOC-Type-List
   TLV, defined in [RFC8697] Section 4.1, containing the value (6),
   corresponding to the SRPA Association Type.  Otherwise the PCEP
   speaker MUST assume that the remote PCEP peer does not support SRPA
   and MUST NOT send the SRPA to that remote peer.

   A given LSP MUST belong to at most one SRPA, since an SR Policy
   Candidate Path cannot belong to multiple SR Policies.  If a PCEP
   speaker receives a PCEP message requesting to join more than one SRPA
   for the same LSP, then the PCEP speaker MUST send a PCErr message
   with Error-Type = 26 "Association Error", Error-Value = 7 "Cannot
   join the association group".

4.1.  Association Parameters

   As per [RFC9256], an SR Policy is identified through the tuple
   <headend, color, endpoint>.  The headend is encoded as the
   Association Source in the ASSOCIATION object and the color and
   endpoint are encoded as part of Extended Association ID TLV.

   The Association Parameters (see Section 2) consist of:

   *  Association Type: set to 6 "SR Policy Association".

   *  Association Source (IPv4/IPv6): set to the headend IP address.

   *  Association ID (16-bit): set to "1" (this 16-bit field is not
      utilized, just set to a value).

   *  Extended Association ID TLV: encodes the Color and Endpoint of the
      SR Policy.





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   The Association Source MUST be set to the headend value of the SR
   Policy, as defined in [RFC9256] Section 2.1.  If the PCC receives a
   PCInit message with the Association Source set not to the headend IP
   but to some globally unique IP address that the headend owns, then
   the PCC SHOULD accept the PCInit message and create the SRPA with the
   Association Source that was sent in the PCInit message.

   The 16-bit Association ID field in the ASSOCIATION object MUST be set
   to the value of "1".

   The Extended Association ID TLV MUST be included and it MUST be in
   the following format:

       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 = 31           |       Length = 8 or 20        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Color                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           Endpoint                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Extended Association ID TLV format

   Type: Extended Association ID TLV, type = 31.

   Length: Either 8 or 20, depending on whether IPv4 or IPv6 address is
   encoded in the Endpoint.

   Color: SR Policy color value, non-zero as per [RFC9256] Section 2.1.

   Endpoint: can be either IPv4 or IPv6.  This value MAY be different
   from the one contained in the END-POINTS object, or in the LSP-
   IDENTIFIERS TLV.

   If the PCEP speaker receives an SRPA object whose Association
   Parameters do not follow the above specification, then the PCEP
   speaker MUST send PCErr message with Error-Type = 26 "Association
   Error", Error-Value = TBD7 "SR Policy Identifier Mismatch".

   The purpose of choosing the Association Parameters in this way is to
   guarantee that there is no possibility of a race condition when
   multiple PCEP speakers want to create the same SR Policy at the same
   time.  By adhering to this format, all PCEP speakers come up with the
   same Association Parameters independently of each other.  Thus, there
   is no chance that different PCEP speakers will come up with different
   Association Parameters for the same SR Policy.



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   The computed destination of the SR Policy Candidate Path MAY differ
   from the Endpoint contained in the <headend, color, endpoint> tuple.
   An example use case is to terminate the SR Policy before reaching the
   Endpoint and have decapsulated traffic go the rest of the way to the
   Endpoint node using the native IGP path(s).  In this example, the
   destination of the SR Policy Candidate Paths will be some node before
   the Endpoint, but the Endpoint value is still used at the head-end to
   steer traffic with that Endpoint IP into the SR Policy.  Destination
   of the SR Policy Candidate Path is signaled using the END-POINTS
   object and/or LSP-IDENTIFIERS TLV, as per the usual PCEP procedures.
   When neither END-POINTS object nor LSP-IDENTIFIERS TLV is present,
   the PCEP speaker MUST extract the destination from the Endpoint field
   in the SRPA Extended Association ID TLV.

4.2.  Association Information

   The SRPA object contains the following TLVs:

   *  SRPOLICY-POL-NAME TLV: (optional) encodes SR Policy Name string.

   *  SRPOLICY-CPATH-ID TLV: (mandatory) encodes SR Policy Candidate
      Path Identifier.

   *  SRPOLICY-CPATH-NAME TLV: (optional) encodes SR Policy Candidate
      Path string name.

   *  SRPOLICY-CPATH-PREFERENCE TLV: (optional) encodes SR Policy
      Candidate Path preference value.

   Of these new TLVs, SRPOLICY-CPATH-ID TLV is mandatory.  When a
   mandatory TLV is missing from the SRPA object, the PCEP speaker MUST
   send a PCErr message with Error-Type = 6 "Mandatory Object Missing",
   Error-Value = TBD6 "Missing SR Policy Mandatory TLV".

   Unless specifically stated otherwise, the TLVs listed in the
   following sub-sections are assumed to be single instance.  Meaning,
   only one instance of the TLV SHOULD be present in the object and only
   the first instance of the TLV SHOULD be interpreted and subsequent
   instances SHOULD be ignored.

4.2.1.  SR Policy Name TLV

   The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPA object.








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       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       SR Policy Name                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: The SRPOLICY-POL-NAME TLV format

   Type: 56 for "SRPOLICY-POL-NAME" TLV.

   Length: indicates the length of the value portion of the TLV in
   octets and MUST be greater than 0.  The TLV MUST be zero-padded so
   that the TLV is 4-octet aligned.

   SR Policy Name: SR Policy name, as defined in [RFC9256].  It SHOULD
   be a string of printable ASCII characters, without a NULL terminator.

4.2.2.  SR Policy Candidate Path Identifier TLV

   The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPA object.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Proto. Origin |                      MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Originator ASN                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                       Originator Address                      |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Discriminator                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: The SRPOLICY-CPATH-ID TLV format

   Type: 57 for "SRPOLICY-CPATH-ID" TLV.

   Length: 28.




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   Protocol Origin: 8-bit value that encodes the protocol origin, as
   specified in Section 6.5.  Note that in PCInit messages, the Protocol
   Origin is always set to "PCEP".

   Originator ASN: Represented as 4 byte number, part of the originator
   identifier, as specified in [RFC9256] Section 2.4.  When sending
   PCInit, the PCE is acting as the originator and therefore SHOULD set
   this to an ASN that it belongs to.

   Originator Address: Represented as 128 bit value where IPv4 address
   are encoded in lowest 32 bits, part of the originator identifier, as
   specified in [RFC9256] Section 2.4.  When sending PCInit, the PCE is
   acting as the originator and therefore SHOULD set this to an address
   that it owns.

   Discriminator: 32-bit value that encodes the Discriminator of the
   Candidate Path.  This is the field that mainly distinguishes
   different SR Candidate Paths, coming from the same originator.  It is
   allowed to be any number in the 32-bit range.

4.2.3.  SR Policy Candidate Path Name TLV

   The SRPOLICY-CPATH-NAME TLV is an optional TLV for the SRPA object.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                 SR Policy Candidate Path Name                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 4: The SRPOLICY-CPATH-NAME TLV format

   Type: 58 for "SRPOLICY-CPATH-NAME" TLV.

   Length: indicates the length of the value portion of the TLV in
   octets and MUST be greater than 0.  The TLV MUST be zero-padded so
   that the TLV is 4-octet aligned.

   SR Policy Candidate Path Name: SR Policy Candidate Path Name, as
   defined in [RFC9256].  It SHOULD be a string of printable ASCII
   characters, without a NULL terminator.






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4.2.4.  SR Policy Candidate Path Preference TLV

   The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPA
   object.  If the TLV is absent, then default Preference value is 100,
   as per Section 2.7 of [RFC9256].

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Preference                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 5: The SRPOLICY-CPATH-PREFERENCE TLV format

   Type: 59 for "SRPOLICY-CPATH-PREFERENCE" TLV.

   Length: 4.

   Preference: Numerical preference of the Candidate Path.

5.  Other Mechanisms

   This section describes mechanisms that are standardized for SR
   Policies in [RFC9256], but do not make use of the SRPA for signaling
   in PCEP.  Since SRPA is not used, there needs to be a separate
   capability negotiation.

   Unless specifically stated otherwise, the TLVs listed in the
   following sub-sections are assumed to be single instance.  Meaning,
   only one instance of the TLV SHOULD be present in the object and only
   the first instance of the TLV SHOULD be interpreted and subsequent
   instances SHOULD be ignored.

5.1.  SR Policy Capability TLV

   The SRPOLICY-CAPABILITY TLV is an optional TLV for the OPEN object.
   It is used at session establishment time to learn the other PCEP
   peer's capabilities with respect to SR Policy.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                   |L|S|I|E|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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                Figure 6: The SRPOLICY-CAPABILITY TLV format

   Type: TBD4 for "SRPOLICY-CAPABILITY TLV.

   Length: 4.

   P-Flag: PCEP speaker supports the COMPUTATION-PRIORITY TLV with SR
   Policy, see Section 5.2.

   E-Flag: PCEP speaker supports the ENLP TLV with SR Policy, see
   Section 5.3.

   I-Flag: PCEP speaker supports INVALIDATION TLV with SR Policy, see
   Section 5.4.

   S-Flag: PCEP speaker supports "Specified-BSID-only" behavior with SR
   Policy, see Section 5.5.

   L-Flag: PCEP speaker supports stateless (PCReq/PCRep) operations with
   SR Policy, see Section 5.6.

5.2.  Computation Priority TLV

   The COMPUTATION-PRIORITY TLV is an optional TLV for the LSP object.
   It is used to signal the numerical computation priority, as specified
   in Section 2.12 of [RFC9256].  If the TLV is absent from the LSP
   object, a default Priority value of 128 is used.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Priority    |                     MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7: The COMPUTATION-PRIORITY TLV format

   Type: TBD1 for "COMPUTATION-PRIORITY" TLV.

   Length: 4.

   Priority: Numerical priority with which this LSP is to be recomputed
   by the PCE upon topology change.







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5.3.  Explicit Null Label Policy (ENLP) TLV

   To steer an unlabeled IP packet into an SR policy, it is necessary to
   create a label stack for that packet, and push one or more labels
   onto that stack.  The Explicit NULL Label Policy (ENLP) TLV is an
   optional TLV used to indicate whether an Explicit NULL Label
   [RFC3032] must be pushed on an unlabeled IP packet before any other
   labels.  The contents of this TLV are used by the SRPM as described
   in section 4.1 of [RFC9256].  If an ENLP TLV is not present, the
   decision of whether to push an Explicit NULL label on a given packet
   is a matter of local configuration.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    ENLP        |                     MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: The Explicit Null Label Policy (ENLP) TLV format

   Type: TBD2 for "ENLP" TLV.

   Length: 4.

   ENLP (Explicit NULL Label Policy): Indicates whether Explicit NULL
   labels are to be pushed on unlabeled IP packets that are being
   steered into a given SR policy.  This field has one of the following
   values:

   *  0: Reserved.

   *  1: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet,
      but do not push an IPv6 Explicit NULL label on an unlabeled IPv6
      packet.

   *  2: Push an IPv6 Explicit NULL label on an unlabeled IPv6 packet,
      but do not push an IPv4 Explicit NULL label on an unlabeled IPv4
      packet.

   *  3: Push an IPv4 Explicit NULL label on an unlabeled IPv4 packet,
      and push an IPv6 Explicit NULL label on an unlabeled IPv6 packet.

   *  4: Do not push an Explicit NULL label.

   *  5 - 255: Reserved.




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   The ENLP reserved values may be used for future extensions and
   implementations SHOULD ignore the ENLP TLV with these values.  The
   behavior signaled in this TLV MAY be overridden by local
   configuration.  The section 4.1 of [RFC9256] describes the behavior
   on the headend for the handling of the explicit null label.

5.4.  Invalidation TLV

   The INVALIDATION TLV is an optional TLV for the LSP object.  It is
   used to control traffic steering into the LSP during the time when
   the LSP is operationally down/invalid.  In the context of SR Policy,
   this TLV facilitates the "Drop upon invalid" behavior, specified in
   Section 8.2 of [RFC9256].  Normally, if the LSP is down/invalid then
   it stops attracting traffic and traffic that is originally destined
   for that LSP is redirected somewhere else, such as via IGP or via
   another LSP.  The "Drop upon invalid" behavior specifies that the LSP
   keeps attracting traffic and the traffic has to be dropped at the
   head-end.  Such an LSP is said to be "in drop state".  While in the
   drop state, the LSP operational state is "UP", as indicated by the
   O-flag in the LSP object.  However the ERO object MAY be empty, if no
   valid path has been computed.

   The INVALIDATION TLV is used in both directions between PCEP peers:

   *  PCE -> PCC: PCE specifies to the PCC under what conditions the LSP
      should enter the drop state.

   *  PCC -> PCE: PCC reports under what conditions the LSP will enter
      the drop state and the PCC also reports whether the LSP is
      currently in the drop state and if so, for what reason.

   Reasons for entering the drop state are represented by a set of
   flags.

                               0 1 2 3 4 5 6 7
                              +-+-+-+-+-+-+-+-+
                              |       |V|P|F|G|
                              +-+-+-+-+-+-+-+-+

                    Figure 9: Invalidation Reasons Flags

   *  G: Generic - does not fit into any other categories below.

   *  F: First-hop resolution failure - head-end first hop resolution
      has failed.

   *  P: Path computation failure - no path was computed for the LSP.




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   *  V: Verification failure - OAM/PM/BFD path verification has
      indicated a breakage.

       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              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Inval Reason  |   Drop Upon   |              MBZ              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 10: The INVALIDATION TLV format

   Type: TBD3 for "INVALIDATION" TLV.

   Length: 4.

   Inval Reason: contains "Invalidation Reasons Flags" which encode the
   reason(s) why the LSP is currently invalidated.  This field can be
   set to non-zero values only by the PCC, it MUST be set to 0 by the
   PCE and ignored by the PCC.

   Drop Upon: contains "Invalidation Reasons Flags" for conditions that
   SHOULD cause the LSP to enter drop state.  This field can be set to
   non-zero values by both PCC and PCE.  When the G-flag is set, this
   indicates that the LSP is to go into Drop upon invalid state for any
   reason.  I.e., when the PCE does not wish to distinguish any reason
   for LSP invalidation and just simply wants it to always go into drop
   state whenever the LSP is down.  Note that when the G-flag is set,
   the values of the other flags are irrelevant.

   Note that out of all the "Invalidation Reasons Flags", only the
   G-flag (Generic) MUST be supported.  The other flags can simply be
   ignored if they are not supported by the PCEP speaker.  For example,
   suppose the PCC only supports P-flag and G-flag.  When this PCC
   receives this TLV with Drop Upon set to 0x6 (P,F), then the PCC
   responds with Drop Upon = 0x4 (P).  When this PCC receives this TLV
   with Drop Upon set to 0x7 (P,F,G), then the PCC responds with Drop
   Upon = 0x5 (P,G).

5.5.  Specified-BSID-only

   Specified-BSID-only functionality is defined in Section 6.2.3 of
   [RFC9256].  When specified-BSID-only is enabled for a particular
   binding SID, it means that the given binding SID is required to be
   allocated and programmed for the LSP to be operationally up.  If the
   binding SID cannot be allocated or programmed for some reason, then
   the LSP must stay down.



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   To signal specified-BSID-only, a new bit: S (Specified-BSID-only) is
   allocated in the "TE-PATH-BINDING TLV Flag field" of the TE-PATH-
   BINDING TLV.  When this bit is set for a particular BSID, it means
   that the BSID follows the Specified-BSID-only behavior.  It is
   possible to have a mix of BSIDs for the same LSP: some with S=1 and
   some with S=0.

5.6.  Stateless Operation

   [RFC8231] Section 5.8.2, allows delegation of an LSP in operationally
   down state, but at the same time mandates the use of PCReq before
   sending PCRpt.  This document modifies the procedure of [RFC8231]
   Section 5.8.2, for SR Policies we make sending of PCReq before PCRpt
   OPTIONAL.  Thus, when a PCC wants to delegate an SR Policy LSP, it
   MAY proceed directly to sending PCRpt, without first sending PCReq
   and waiting for PCRep.  This has the advantage of reducing the number
   of PCEP messages and simplifying the implementation.

   Furthermore, a PCEP speaker is not required to support PCReq/PCRep at
   all for SR Policies.  The PCEP speaker can indicate support for
   PCReq/PCRep via the "L-Flag" in the SRPOLICY-CAPABILITY TLV (See
   Section 5.1).  When this flag is cleared, or when the SRPOLICY-
   CAPABILITY TLV is absent, the given peer SHOULD NOT be sent PCReq/
   PCRep messages for SR Policy LSPs.  Conversely when this flag is set,
   the peer can receive and process PCReq/PCRep messages for SR Policy
   LSPs.

   The above applies only to SR Policy LSPs and does not affect other
   LSP types, such as RSVP-TE LSPs.  For other LSP types, [RFC8231]
   Section 5.8.2 continues to apply.

6.  IANA Considerations

6.1.  Association Type

   This document defines a new association type: SR Policy Association.
   IANA is requested to make the following codepoint assignment in the
   "ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
   Computation Element Protocol (PCEP) Numbers" registry:

   +-----------+-------------------------------------------+-----------+
   | Type      | Name                                      | Reference |
   +-----------+-------------------------------------------+-----------+
   | 6         | SR Policy Association                     | This.I-D  |
   +-----------+-------------------------------------------+-----------+






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6.2.  PCEP TLV Type Indicators

   This document defines four new TLVs for carrying additional
   information about SR Policy and SR Candidate Paths.  IANA is
   requested to make the assignment of a new value for the existing
   "PCEP TLV Type Indicators" registry as follows:

   +-----------+-------------------------------------------+-----------+
   | Value     | Description                               | Reference |
   +-----------+-------------------------------------------+-----------+
   | 56        | SRPOLICY-POL-NAME                         | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | 57        | SRPOLICY-CPATH-ID                         | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | 58        | SRPOLICY-CPATH-NAME                       | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | 59        | SRPOLICY-CPATH-PREFERENCE                 | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | TBD1      | COMPUTATION-PRIORITY                      | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | TBD2      | EXPLICIT-NULL-LABEL-POLICY                | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | TBD3      | INVALIDATION                              | This.I-D  |
   +-----------+-------------------------------------------+-----------+
   | TBD4      | SRPOLICY-CAPABILITY                       | This.I-D  |
   +-----------+-------------------------------------------+-----------+

6.3.  PCEP Errors

   This document defines one new Error-Value within the "Mandatory
   Object Missing" Error-Type and two new Error-Values within the
   "Association Error" Error-Type.  IANA is requested to allocate new
   error values within the "PCEP-ERROR Object Error Types and Values"
   sub-registry of the PCEP Numbers registry, as follows:

















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   +------------+------------------+-----------------------+-----------+
   | Error-Type | Meaning          | Error-value           | Reference |
   +------------+------------------+-----------------------+-----------+
   | 6          | Mandatory Object |                       | [RFC5440] |
   |            | Missing          |                       |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | TBD6: Missing SR      | This.I-D  |
   |            |                  | Policy Mandatory TLV  |           |
   +------------+------------------+-----------------------+-----------+
   | 26         | Association      |                       | [RFC8697] |
   |            | Error            |                       |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | TBD7: SR Policy       | This.I-D  |
   |            |                  | Identifers Mismatch   |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | TBD8: SR Policy       | This.I-D  |
   |            |                  | Candidate Path        |           |
   |            |                  | Identifier Mismatch   |           |
   +------------+------------------+-----------------------+-----------+

6.4.  TE-PATH-BINDING TLV Flag field

   IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV
   Flag field" sub-registry of the PCEP Numbers registry, as follows:

   +------------+------------------------------------------+-----------+
   | Bit position | Description                            | Reference |
   +--------------+----------------------------------------+-----------+
   | TBD9         | S (Specified-BSID-only)                | This.I-D  |
   +--------------+----------------------------------------+-----------+

6.5.  SR Policy Candidate Path Protocol Origin field

   This document requests IANA to maintain a new registry under "Segment
   Routing Parameters" registry group.  New values are to be assigned by
   "Standards Action" [RFC8126].  The new registry is called "SR Policy
   Protocol Origin".  The registry contains the following codepoints,
   with initial values, to be assigned by IANA with the reference set to
   this document:












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   +------------+------------------------------------------------------+
   | Value        | Description                                        |
   +--------------+----------------------------------------------------+
   | 0            | Reserved (not to be used)                          |
   +--------------+----------------------------------------------------+
   | 1-9          | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 10           | PCEP                                               |
   +--------------+----------------------------------------------------+
   | 11-19        | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 20           | BGP SR Policy                                      |
   +--------------+----------------------------------------------------+
   | 21-29        | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 30           | Configuration (CLI, YANG model via NETCONF, etc.)  |
   +--------------+----------------------------------------------------+
   | 31-250       | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 251 - 255    | Private Use (not to be assigned by IANA)           |
   +--------------+----------------------------------------------------+

7.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to RFC 7942.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".





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7.1.  Cisco

   *  Organization: Cisco Systems

   *  Implementation: IOS-XR PCC and PCE.

   *  Description: All features supported except Computation Priority,
      Explicit NULL and Invalidation Drop.

   *  Maturity Level: Production.

   *  Coverage: Full.

   *  Contact: mkoldych@cisco.com

7.2.  Juniper

   *  Organization: Juniper Networks

   *  Implementation: PCC and PCE.

   *  Description: Everything in -05 except SR Policy Name TLV and SR
      Policy Candidate Path Name TLV.

   *  Maturity Level: Production.

   *  Coverage: Partial.

   *  Contact: cbarth@juniper.net

8.  Security Considerations

   This document defines one new type for ASSOCIATION object, which does
   not add any new security concerns beyond those discussed in
   [RFC5440], [RFC8231], [RFC8664] and [RFC8697] in itself.

   The information carried in the SRPA object, as per this document is
   related to SR Policy.  It often reflects information that can also be
   derived from the SR Database, but association provides a much easier
   grouping of related LSPs and messages.  The SRPA could provide an
   adversary with the opportunity to eavesdrop on the relationship
   between the LSPs.  Thus securing the PCEP session using Transport
   Layer Security (TLS) [RFC8253], as per the recommendations and best
   current practices in [RFC7525], is RECOMMENDED.







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9.  Acknowledgement

   Would like to thank Stephane Litkowski, Boris Khasanov, Abdul Rehman,
   Alex Tokar, Praveen Kumar and Tom Petch for review and suggestions.

10.  References

10.1.  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>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

   [RFC8697]  Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships between Sets of Label Switched Paths
              (LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
              <https://www.rfc-editor.org/info/rfc8697>.






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   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

10.2.  Informative References

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", RFC 7525, DOI 10.17487/RFC7525, May 2015,
              <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [I-D.ietf-pce-multipath]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
              Extensions for Signaling Multipath Information", Work in
              Progress, Internet-Draft, draft-ietf-pce-multipath-10, 16
              January 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-pce-multipath-10>.

Appendix A.  Contributors

















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   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   Email: dhruv.ietf@gmail.com

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing, 10095
   China

   Email: chengli13@huawei.com

   Samuel Sidor
   Cisco Systems, Inc.
   Eurovea Central 3.
   Pribinova 10
   811 09 Bratislava
   Slovakia

   Email: ssidor@cisco.com

Authors' Addresses

   Mike Koldychev
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata Ontario K2K 3E8
   Canada
   Email: mkoldych@proton.me


   Siva Sivabalan
   Ciena Corporation
   385 Terry Fox Dr.
   Kanata Ontario K2K 0L1
   Canada
   Email: ssivabal@ciena.com


   Colby Barth
   Juniper Networks, Inc.
   Email: cbarth@juniper.net





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   Shuping Peng
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: pengshuping@huawei.com


   Hooman Bidgoli
   Nokia
   Email: hooman.bidgoli@nokia.com







































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