[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03

PCE Working Group                                           M. Koldychev
Internet-Draft                                              S. Sivabalan
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: January 3, 2020                                        C. Barth
                                                  Juniper Networks, Inc.
                                                                   C. Li
                                                     Huawei Technologies
                                                           July 02, 2019


    PCEP extension to support Segment Routing Policy Candidate Paths
              draft-barth-pce-segment-routing-policy-cp-03

Abstract

   This document introduces a mechanism to specify an Segment Routing
   (SR) policy, as a collection of SR candidate paths.  An SR policy is
   identified by <headend, color, end-point> tuple.  An SR policy can
   contain one or more candidate paths where each candidate path is
   identified in PCEP via an PLSP-ID.  This document proposes extension
   to PCEP to support association among candidate paths of a given SR
   policy.  The mechanism proposed in this document is applicable to
   both MPLS and IPv6 data planes of SR.

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."

   This Internet-Draft will expire on January 3, 2020.



Koldychev, et al.        Expires January 3, 2020                [Page 1]


Internet-Draft                  SR Policy                      July 2019


Copyright Notice

   Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Group Candidate Paths belonging to the same SR policy . .   5
     3.2.  Instantiation of SR policy candidate paths  . . . . . . .   5
     3.3.  Avoid computing lower preference candidate paths  . . . .   5
     3.4.  Minimal signaling overhead  . . . . . . . . . . . . . . .   5
   4.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  SR Policy Association Group . . . . . . . . . . . . . . . . .   7
     5.1.  SR Policy Identifiers TLV . . . . . . . . . . . . . . . .   8
     5.2.  SR Policy Name TLV  . . . . . . . . . . . . . . . . . . .   9
     5.3.  SR Policy Candidate Path Identifiers TLV  . . . . . . . .  10
     5.4.  SR Policy Candidate Path Preference TLV . . . . . . . . .  11
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  PCC Initiated SR Policy with single candidate-path  . . .  11
     6.2.  PCC Initiated SR Policy with multiple candidate-paths . .  12
     6.3.  PCE Initiated SR Policy with single candidate-path  . . .  12
     6.4.  PCE Initiated SR Policy with multiple candidate-paths . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  14
     7.2.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .  14
     7.3.  SRPAG TLVs  . . . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17





Koldychev, et al.        Expires January 3, 2020                [Page 2]


Internet-Draft                  SR Policy                      July 2019


1.  Introduction

   Path Computation Element (PCE) Communication Protocol (PCEP)
   [RFC5440] enables the communication between a Path Computation Client
   (PCC) and a Path Control Element (PCE), or between two PCEs based on
   the PCE architecture [RFC4655].

   PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
   of extensions to PCEP to enable active control of Multiprotocol Label
   Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
   tunnels.  [RFC8281] describes the setup and teardown of PCE-initiated
   LSPs under the active stateful PCE model, without the need for local
   configuration on the PCC, thus allowing for dynamic centralized
   control of a network.

   PCEP Extensions for Segment Routing [I-D.ietf-pce-segment-routing]
   specifies extensions to the Path Computation Element Protocol (PCEP)
   that allow a stateful PCE to compute and initiate Traffic Engineering
   (TE) paths, as well as a PCC to request a path subject to certain
   constraint(s) and optimization criteria in SR networks.

   PCEP Extensions for Establishing Relationships Between Sets of LSPs
   [I-D.ietf-pce-association-group] introduces a generic mechanism to
   create a grouping of LSPs which can then be used to define
   associations between a set of LSPs and a set of attributes (such as
   configuration parameters or behaviors) and is equally applicable to
   stateful PCE (active and passive modes) and stateless PCE.

   Segment Routing Policy for Traffic Engineering
   [I-D.ietf-spring-segment-routing-policy] details the concepts of SR
   Policy and approaches to steering traffic into an SR Policy.

   An SR policy contains one or more candidate paths where one or more
   such paths can be computed via PCE.  This document specifies PCEP
   extensions to signal additional information to map candidate paths to
   their SR policies.  Each candidate path maps to a unique PLSP-ID in
   PCEP.  By associating multiple candidate paths together, a PCE
   becomes aware of the hierarchical structure of an SR policy.  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.  This is accomplished via the use
   of the existing PCEP Association object, by defining a new
   association type specifically for associating SR candidate paths into
   a single SR policy.

   [Editor's Note- Currently it is assumed that each candidate path has
   only one ERO (SID-List) within the scope of this document.  A future




Koldychev, et al.        Expires January 3, 2020                [Page 3]


Internet-Draft                  SR Policy                      July 2019


   update or another document will deal with a way to allow multiple
   ERO/SID-Lists for a candidate path within PCEP.]

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
      [I-D.ietf-spring-segment-routing-policy].

   Association parameters:  As described in
      [I-D.ietf-pce-association-group], the combination of the mandatory
      fields Association type, Association ID and Association Source in
      the ASSOCIATION object uniquely identify the association group.
      If the optional TLVs - Global Association Source or Extended
      Association ID are included, then they MUST be included in
      combination with mandatory fields to uniquely identify the
      association group.

   Association information:  As described in
      [I-D.ietf-pce-association-group], the ASSOCIATION object could
      also include other optional TLVs based on the association types,
      that provides 'information' related to the association type.

   PCC:  Path Computation Client.  Any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   PCEP:  Path Computation Element Protocol.

3.  Motivation

   The new Association Type (SR Policy Association) and the new TLVs for
   the ASSOCIATION object, defined in this document, allow a PCEP peer
   to exchange additional parameters of SR candidate paths and of their
   parent SR policy.  For the SR policy, the parameters are: color and
   endpoint.  For the candidate path, the parameters are: protocol
   origin, originator, discriminator and preference.
   [I-D.ietf-spring-segment-routing-policy] describes the concept of SR
   Policy and these parameters.

   The motivation for signaling these parameters is summarized in the
   following subsections.



Koldychev, et al.        Expires January 3, 2020                [Page 4]


Internet-Draft                  SR Policy                      July 2019


3.1.  Group Candidate Paths belonging to the same SR policy

   Since each candidate path of an SR policy appears as a different LSP
   (identified via a PLSP-ID) in PCEP, it is useful to group together
   all the candidate paths that belong to the same SR policy.
   Furthermore, it is useful for the PCE to have knowledge of the SR
   candidate path parameters such as color, protocol origin,
   discriminator, and preference.

3.2.  Instantiation of SR policy candidate paths

   A PCE may want to instantiate one or more candidate paths on the PCC,
   as specified in [RFC8281].  In this scenario, the PCE needs to signal
   to a PCC <headend, color, end-point, originator, discriminator,
   preference> tuple using which the PCC can instantiate a candidate
   path for the SR policy identified.  Current PCEP standards (as of the
   time of this writing) do not provide a way to signal color and
   preference.  Although end-point can be signaled via the PCEP END-
   POINTS object, this object may not be suitable because the end-point
   to which the path is computed is not required to be the same IPv4/
   IPv6 address as the actual endpoint of the SR policy.  Thus, a
   separate way to specify SR policy's end-point is provided in this
   document.

3.3.  Avoid computing lower preference candidate paths

   When a PCE knows that a given set of candidate paths all belong to
   the same SR policy, then path computation MAY be done on only the
   highest preference candidate-path(s).  Path computation for lower
   preference paths is not necessary if one or two higher preference
   paths are already computed.  Since computing their paths will not
   affect traffic steering, it MAY be postponed until the higher
   preference paths become invalid, thus saving computation resources on
   the PCE.

3.4.  Minimal signaling overhead

   When an SR policy contains multiple candidate paths computed by a
   PCE, such candidate paths can be created, updated and deleted
   independently of each other.  This is achieved by making each
   candidate path correspond to a unique LSP (identified via PLSP-ID).
   For example, if an SR policy has 4 candidate paths, then if the PCE
   wants to update one of those candidate paths, only one set of PCUpd
   and PCRpt messages needs to be exchanged.







Koldychev, et al.        Expires January 3, 2020                [Page 5]


Internet-Draft                  SR Policy                      July 2019


4.  Overview

   As per [I-D.ietf-pce-association-group], LSPs are placed into an
   association group.  In this document, each LSP corresponds to a
   candidate path of an SR policy, and the association group corresponds
   to the SR policy itself.  Segment-lists within a candidate path are
   not represented by different LSPs (and identified via PLSP-IDs).

   [Editor's Note - The subject of encoding multiple segment lists
   within a candidate path is left to a future document and is not
   specified in this document.  It is not a good idea to have each
   segment-list correspond to a different LSP/PLSP-ID, because when the
   PCC wants to get a path, it must know in advance how many multipaths
   (i.e., segment-lists) there will be and create that many LSPs/PLSP-
   IDs.  For example, if the PCC supports 32 multipaths, then it must
   delegate 32 LSPs/PLSP-IDs for every candidate path, which may not be
   scalable.]

   A new Association Type is defined in this document, based on the
   generic ASSOCIATION object.  Association type = TBD1 "SR Policy
   Association Type" for SR Policy Association Group (SRPAG).

   The SRPAG Association is only meant to be used for SR LSPs and with
   PCEP peers which advertise SR capability.

   An Association object of SRPAG group contains TLVs that carry
   Association Information.  The association information can be
   subdivided into three parts: Policy identifiers, Candidate path
   identifiers, and Candidate path attributes.

   Policy Identifiers uniquely identify the SR policy to which a given
   LSP belongs, within the context of the head-end.  Policy Identifiers
   MUST be the same for all candidate paths in the same SRPAG.  Policy
   Identifiers MUST NOT change for a given LSP during its lifetime.
   Policy Identifiers MUST be different for different SRPAG
   associations.  When these rules are not satisfied, the PCE MUST send
   a PCErr message with Error Code = 26 "Association Error", Error Type
   = TBD6 "Conflicting SRPAG TLV".  Policy Identifiers consist of:

   o  Color of SR policy.

   o  End-point of SR policy.

   o  Optionally, the policy name.

   Candidate Path Identifiers uniquely identify the SR candidate path
   within the context of an SR policy.  Candidate path Identifiers MUST
   NOT change for a given LSP during its lifetime.  Candidate path



Koldychev, et al.        Expires January 3, 2020                [Page 6]


Internet-Draft                  SR Policy                      July 2019


   Identifiers MUST be different for different LSPs within the same
   SRPAG.  When these rules are not satisfied, the PCE MUST send a PCErr
   message with Error Code = 26 "Association Error", Error Type = TBD6
   "Conflicting SRPAG TLV".  Candidate path Identifiers consist of:

   o  Protocol Origin of candidate path.

   o  Originator of candidate path.

   o  Discriminator of candidate path.

   Candidate Path Attributes MUST NOT be used to identify the candidate
   path.  Candidate path attributes carry additional information about
   the candidate path and MAY change during the lifetime of the LSP.
   Candidate path Attributes consist of:

   o  Preference of candidate path.

   As described in [RFC8231], an LSP is uniquely identified in PCEP via
   PLSP-ID.

   A mapping between the Association Parameters (see Section 2) and
   Policy Identifiers (the Color and End-point) needs to be maintained.
   The mapping is left up to the implementation.  An implementation MAY
   choose Association Parameters in such a way that every possible Color
   and End-point maps to a unique value of Association Parameters, which
   may require the use of Extended Association ID TLV.  Alternatively,
   an implementation MAY implement a lookup table to generate
   Association Parameters incrementally as new Color and End-point
   values are created, which may not require the use of Extended
   Association ID TLV.

   As per the processing rules specified in section 5.4 of
   [I-D.ietf-pce-association-group], if a PCEP speaker does not support
   the SRPAG association type, it MUST return a PCErr message with
   Error-Type 26 (Early allocation by IANA) "Association Error" and
   Error-Value 1 "Association-type is not supported".  Please note that
   the corresponding PCEP session is not reset.

5.  SR Policy Association Group

   Two ASSOCIATION object types for IPv4 and IPv6 are defined in
   [I-D.ietf-pce-association-group].  The ASSOCIATION object includes
   "Association type" indicating the type of the association group.
   This document adds a new Association type.

   Association type = TBD1 "SR Policy Association Type" for SR Policy
   Association Group (SRPAG).



Koldychev, et al.        Expires January 3, 2020                [Page 7]


Internet-Draft                  SR Policy                      July 2019


   The operator configured Association Range SHOULD NOT be set for this
   association type and MUST be ignored.

   SRPAG MUST carry additional TLVs to communicate Association
   Information.  This document specifies four new TLVs to carry
   Association Information: SRPOLICY-POL-ID TLV, SRPOLICY-POL-NAME TLV,
   SRPOLICY-CPATH-ID TLV, SRPOLICY-CPATH-PREFERENCE TLV.  These four
   TLVs encode the Policy Identifiers, Policy name, Candidate path
   Identifiers and Candidate path Preference, respectively.  When any of
   the mandatory TLVs are missing from the SRPAG association object, the
   PCE MUST send a PCErr message with Error Code = 26 "Association
   Error", Error Type = TBD7 "Missing mandatory SRPAG TLV".

   A given LSP MUST belong to at most one SRPAG, since a candidate path
   cannot belong to multiple SR policies.  If a PCEP speaker receives a
   PCEP message with more than one SRPAG for an LSP, then the PCEP
   speaker MUST send a PCErr message with Error-Type 26 "Association
   Error" and Error-Value TBD8 "Multiple SRPAG for one LSP".  If the
   message is a PCRpt message, then the PCEP speaker MUST close the PCEP
   connection.  Closing the PCEP connection is necessary because
   ignoring PCRpt messages may lead to inconsistent LSP DB state between
   the two PCEP peers.

   If the PCEP speaker receives the SRPAG association when the SR
   capability (as per [I-D.ietf-pce-segment-routing] or
   [I-D.negi-pce-segment-routing-ipv6]) was not exchanged, the PCEP
   speaker MUST send a PCErr message with Error-Type 26 "Association
   Error" and Error-Value TBD9 "Use of SRPAG without SR capability
   exchange".  If the Path Setup Type (PST) of the LSP in SRPAG is not
   set to SR or SRv6, then the PCEP speaker MUST send a PCErr message
   with Error-Type 26 "Association Error" and Error-Value TBD10 "non-SR
   LSP in SRPAG".

5.1.  SR Policy Identifiers TLV

   The SRPOLICY-POL-ID TLV is a mandatory TLV for the SRPAG Association.
   Only one SRPOLICY-POL-ID TLV can be carried and only the first
   occurrence is processed and any others MUST be ignored.













Koldychev, et al.        Expires January 3, 2020                [Page 8]


Internet-Draft                  SR Policy                      July 2019


       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Color                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           End-point                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: The SRPOLICY-POL-ID TLV format

   Type: TBD2 for "SRPOLICY-POL-ID" TLV.

   Length: 8 or 20, depending on length of End-point (IPv4 or IPv6)

   Color: any unsigned 32-bit number.

   End-point: can be either IPv4 or IPv6, depending on whether the
   policy endpoint has IPv4 or IPv6 address.  This value may be
   different from the one contained in the END-POINTS object, or in the
   LSP IDENTIFIERS TLV of the LSP object.  Endpoint is meant to strictly
   correspond to the endpoint of the SR policy, as it is defined in
   [I-D.ietf-spring-segment-routing-policy].

5.2.  SR Policy Name TLV

   The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPAG
   Association.  At most one SRPOLICY-POL-NAME TLV can be carried and
   only the first occurrence is processed and any others MUST be
   ignored.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Policy Name                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: The SRPOLICY-POL-NAME TLV format

   Type: TBD3 for "SRPOLICY-POL-NAME" TLV.






Koldychev, et al.        Expires January 3, 2020                [Page 9]


Internet-Draft                  SR Policy                      July 2019


   Length: indicates the total length 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.

   Policy Name: Policy name, as defined in
   [I-D.ietf-spring-segment-routing-policy].  It SHOULD be a string of
   printable ASCII characters, without a NULL terminator.

5.3.  SR Policy Candidate Path Identifiers TLV

   The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPAG
   Association.  Only one SRPOLICY-CPATH-ID TLV can be carried and only
   the first occurrence is processed and any others MUST be ignored.

       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 |                    Reserved                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Originator ASN                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                       Originator Address                      |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Discriminator                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: The SRPOLICY-CPATH-ID TLV format

   Type: TBD4 for "SRPOLICY-CPATH-ID" TLV.

   Length: 28.

   Protocol Origin: 8-bit value that encodes the protocol origin, as
   specified in [I-D.ietf-spring-segment-routing-policy] Section 2.3.

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

   Originator ASN: Represented as 4 byte number, part of the originator
   identifier, as specified in [I-D.ietf-spring-segment-routing-policy]
   Section 2.4.






Koldychev, et al.        Expires January 3, 2020               [Page 10]


Internet-Draft                  SR Policy                      July 2019


   Originator Address: Represented as 128 bit value where IPv4 address
   are encoded in lowest 32 bits, part of the originator identifier, as
   specified in [I-D.ietf-spring-segment-routing-policy] Section 2.4.

   Discriminator: 32-bit value that encodes the Discriminator of the
   candidate path.

5.4.  SR Policy Candidate Path Preference TLV

   The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPAG
   Association.  Only one SRPOLICY-CPATH-PREFERENCE TLV can be carried
   and only the first occurrence is processed and any others MUST be
   ignored.

       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 4: The SRPOLICY-CPATH-PREFERENCE TLV format

   Type: TBD5 for "SRPOLICY-CPATH-PREFERENCE" TLV.

   Length: 4.

   Preference: Numerical preference of the candidate path, as specified
   in [I-D.ietf-spring-segment-routing-policy] Section 2.7.

   If the TLV is missing, a default preference of 100 as specified in
   [I-D.ietf-spring-segment-routing-policy] is used.

6.  Examples

6.1.  PCC Initiated SR Policy with single candidate-path

   PCReq and PCRep messages are exchanged in the following sequence:

   1.  PCC sends PCReq message to the PCE, encoding the SRPAG
       ASSOCIATION object and TLVs in the PCReq message.

   2.  PCE returns the path in PCRep message, and echoes back the SRPAG
       object that was used in the computation.

   PCRpt and PCUpd messages are exchanged in the following sequence:




Koldychev, et al.        Expires January 3, 2020               [Page 11]


Internet-Draft                  SR Policy                      July 2019


   1.  PCC sends PCRpt message to the PCE, including the LSP object and
       the SRPAG ASSOCIATION object.

   2.  PCE computes path, possibly making use of the Association
       Information from the SRPAG ASSOCIATION object.

   3.  PCE updates the SR policy candidate path's ERO using PCUpd
       message.

6.2.  PCC Initiated SR Policy with multiple candidate-paths

   PCReq and PCRep messages are exchanged using the sequence specified
   in section 6.1 with individual query for each candidate-path.

   PCRpt and PCUpd messages are exchanged in the following sequence:

   1.  Step 1: For each candidate path of the SR policy, the PCC
       generates a different PLSP-ID and symbolic-name and sends
       multiple PCRpt messages (or one message with multiple LSP
       objects) to the PCE.  Each LSP object is followed by SRPAG
       ASSOCIATION object with identical Color and Endpoint values.

   2.  Step 2: PCE takes into account that all the LSPs belong to the
       same SR policy.  PCE prioritizes computation for the highest
       preference LSP and sends PCUpd message(s) back to the PCC.

   3.  Step 3: If a new candidate path is added on the PCC by the
       operator, then a new PLSP-ID and symbolic name is generated for
       that candidate path and a new PCRpt is sent to the PCE.

   4.  Step 4: If an existing candidate path is removed from the PCC by
       the operator, then that PLSP-ID is deleted from the PCE by
       sending PCRpt with the R-flag in the LSP object set.

6.3.  PCE Initiated SR Policy with single candidate-path

   A candidate-path is created using the following steps:

   1.  PCE sends PCInitiate message, as usual containing the SRPAG
       Association object.  PCE needs to generate a symbolic-name for
       this LSP that will not clash with other symbolic names on the
       same PCC.

   2.  PCC uses the color, endpoint and preference from the SRPAG object
       to create a new candidate path.  If no SR policy exists to hold
       the candidate path, then a new SR policy is created to hold the
       new candidate-path.  The Originator of the candidate path is set




Koldychev, et al.        Expires January 3, 2020               [Page 12]


Internet-Draft                  SR Policy                      July 2019


       to be the address of the PCE that is sending the PCInitiate
       message.

   3.  PCC allocates a locally unique PLSP-ID for the newly created
       candidate path.  This PLSP-ID is sent to the PCE in the PCRpt
       message.

   A candidate-path is deleted using the following steps:

   1.  PCE sends PCInitiate message, setting the R-flag in the LSP
       object.

   2.  PCC uses the PLSP-ID from the LSP object to find the candidate
       path and delete it.  If this is the last candidate path under the
       SR policy, then the containing SR policy is deleted as well.

6.4.  PCE Initiated SR Policy with multiple candidate-paths

   A candidate-path is created using the following steps:

   1.  PCE sends a separate PCInitiate message for every candidate path
       that it wants to create, or it sends multiple LSP objects within
       a single PCInitiate message.  Each candidate-path must get a
       unique symbolic-name generated on the PCE.  SRPAG object is sent
       for every LSP in the PCInitiate message.

   2.  PCC creates multiple candidate paths under the same SR policy,
       identified by Color and Endpoint.  PCC generates a unique PLSP-ID
       for every candidate path.

   3.  PCC allocates a locally unique PLSP-ID for each newly created
       candidate path.  This PLSP-ID is sent to the PCE in the PCRpt
       message.

   A candidate path is deleted using the following steps:

   1.  PCE sends PCInitiate message, setting the R-flag in the LSP
       object.

   2.  PCC uses the PLSP-ID from the LSP object to find the candidate
       path and delete it.

7.  IANA Considerations








Koldychev, et al.        Expires January 3, 2020               [Page 13]


Internet-Draft                  SR Policy                      July 2019


7.1.  Association Type

   This document defines a new association type: SR Policy Association
   Group (SRPAG).  IANA is requested to make the assignment of a new
   value for the sub-registry "ASSOCIATION Type Field" (request to be
   created in [I-D.ietf-pce-association-group]), as follows:

   +----------------------+-------------------------+------------------+
   | Association Type     | Association Name        | Reference        |
   | Value                |                         |                  |
   +----------------------+-------------------------+------------------+
   | TBD1                 | SR Policy Association   | This document    |
   +----------------------+-------------------------+------------------+

7.2.  PCEP Errors

   This document defines three 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:

   +-------+----------+-----------------------------+------------------+
   | Error | Error    | Meaning                     | Reference        |
   | Type  | Value    |                             |                  |
   +-------+----------+-----------------------------+------------------+
   | 29    | TBD6     | Conflicting SRPAG TLV       | This document    |
   +-------+----------+-----------------------------+------------------+
   | 29    | TBD7     | Missing mandatory SRPAG TLV | This document    |
   +-------+----------+-----------------------------+------------------+
   | 29    | TBD8     | Multiple SRPAG for one LSP  | This document    |
   +-------+----------+-----------------------------+------------------+
   | 29    | TBD9     | Use of SRPAG without SR     | This document    |
   |       |          | capability exchange         |                  |
   +-------+----------+-----------------------------+------------------+
   | 29    | TBD10    | non-SR LSP in SRPAG         | This document    |
   +-------+----------+-----------------------------+------------------+


7.3.  SRPAG TLVs

   This document defines three 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:







Koldychev, et al.        Expires January 3, 2020               [Page 14]


Internet-Draft                  SR Policy                      July 2019


   +------------+-----------------------------------+------------------+
   | TLV Type   | TLV Name                          | Reference        |
   | Value      |                                   |                  |
   +------------+-----------------------------------+------------------+
   | TBD2       | SRPOLICY-POL-ID                   | This document    |
   +------------+-----------------------------------+------------------+
   | TBD3       | SRPOLICY-POL-NAME                 | This document    |
   +------------+-----------------------------------+------------------+
   | TBD4       | SRPOLICY-CPATH-ID                 | This document    |
   +------------+-----------------------------------+------------------+
   | TBD5       | SRPOLICY-CPATH-PREFERENCE         | This document    |
   +------------+-----------------------------------+------------------+

8.  Security Considerations

   This document defines one new type for association, which do not add
   any new security concerns beyond those discussed in [RFC5440],
   [RFC8231], [I-D.ietf-pce-segment-routing],
   [I-D.negi-pce-segment-routing-ipv6] and
   [I-D.ietf-pce-association-group] in itself.

   The information carried in the SRPAG Association 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 SRPAG
   association could provides 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.

9.  Acknowledgement

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>.





Koldychev, et al.        Expires January 3, 2020               [Page 15]


Internet-Draft                  SR Policy                      July 2019


   [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>.

   [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>.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-03 (work in progress), May 2019.

   [I-D.ietf-pce-association-group]
              Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "PCEP Extensions for
              Establishing Relationships Between Sets of LSPs", draft-
              ietf-pce-association-group-09 (work in progress), April
              2019.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-16 (work in progress),
              March 2019.

10.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.




Koldychev, et al.        Expires January 3, 2020               [Page 16]


Internet-Draft                  SR Policy                      July 2019


   [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.negi-pce-segment-routing-ipv6]
              Negi, M., Li, C., Sivabalan, S., and P. Kaladharan, "PCEP
              Extensions for Segment Routing leveraging the IPv6 data
              plane", draft-negi-pce-segment-routing-ipv6-04 (work in
              progress), February 2019.

Appendix A.  Contributors

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

   Email: dhruv.ietf@gmail.com

Authors' Addresses

   Mike Koldychev
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   Email: mkoldych@cisco.com


   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   Email: msiva@cisco.com


   Colby Barth
   Juniper Networks, Inc.

   Email: cbarth@juniper.net





Koldychev, et al.        Expires January 3, 2020               [Page 17]


Internet-Draft                  SR Policy                      July 2019


   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: chengli13@huawei.com












































Koldychev, et al.        Expires January 3, 2020               [Page 18]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/