



PCE Working Group                                            A. Raghuram
Internet-Draft                                                A. Goddard
Intended status: Standards Track                                    AT&T
Expires: April 15, 2020                                       J. Karthik
                                                            S. Sivabalan
                                                     Cisco Systems, Inc.
                                                                 M. Negi
                                                     Huawei Technologies
                                                        October 13, 2019


  Ability for a Stateful Path Computation Element (PCE) to request and
             obtain control of a Label Switched Path (LSP)
                 draft-ietf-pce-lsp-control-request-11

Abstract

   A Stateful Path Computation Element (PCE) retains information about
   the placement of Multiprotocol Label Switching (MPLS) Traffic
   Engineering Label Switched Paths (TE LSPs).  When a PCE has stateful
   control over LSPs it may send indications to LSP head-ends to modify
   the attributes (especially the paths) of the LSPs.  A Path
   Computation Client (PCC) that has set up LSPs under local
   configuration may delegate control of those LSPs to a stateful PCE.

   There are use-cases in which a stateful PCE may wish to obtain
   control of locally configured LSPs of which it is aware but that have
   not been delegated to the PCE.

   This document describes an extension to the Path Computation Element
   communication Protocol (PCEP) to enable a PCE to make requests for
   such control.

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 April 15, 2020.

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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  LSP Control Request Flag  . . . . . . . . . . . . . . . . . .   4
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Huawei's Proof of Concept based on ONOS . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  SRP Object Flags  . . . . . . . . . . . . . . . . . . . .   8
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .   8
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .   8
     8.2.  Information and Data Models . . . . . . . . . . . . . . .   8
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .   8
     8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .   8
     8.5.  Requirements On Other Protocols . . . . . . . . . . . . .   9
     8.6.  Impact On Network Operations  . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Stateful Path Computation Element (PCE) communication Protocol (PCEP)
   extensions [RFC8231] specifies a set of extensions to PCEP [RFC5440]
   to enable stateful control of Traffic Engineering Label Switched



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   Paths (TE LSPs) between and across PCEP sessions in compliance with
   [RFC4657].  It includes mechanisms to synchronize LSP state between
   Path Computation Clients (PCCs) and PCEs, delegate control of LSPs to
   PCE, and PCE-control of timing and sequence of path computations
   within and across PCEP sessions.  The stateful PCEP defines the
   following two useful network operations:

   o  Delegation: As per [RFC8051], an operation to grant a PCE
      temporary rights to modify a subset of LSP parameters on one or
      more LSPs of a PCC.  LSPs are delegated from a PCC to a PCE and
      are referred to as "delegated" LSPs.

   o  Revocation: As per [RFC8231], an operation performed by a PCC on a
      previously delegated LSP.  Revocation revokes the rights granted
      to the PCE in the delegation operation.

   For Redundant Stateful PCEs (section 5.7.4. of [RFC8231]), during a
   PCE failure, one of the redundant PCE might want to request to take
   control over an LSP.  The redundant PCEs may use a local policy or a
   proprietary election mechanism to decide which PCE would take
   control.  In this case, a mechanism is needed for a stateful PCE to
   request control of one or more LSPs from a PCC, so that a newly
   elected primary PCE can request to take over control.

   In case of virtualized PCEs (vPCEs) running in virtual network
   function (VNF) mode, as the computation load in the network
   increases, a new instance of vPCE could be instantiated to balance
   the current load.  The PCEs could use a proprietary algorithm to
   decide which LSPs to be assigned to the new vPCE.  Thus, having a
   mechanism for the PCE to request control of some LSPs is needed.

   In some deployments, the operator would like to use stateful PCE for
   global optimization algorithms but would still like to keep the
   control of the LSP at the PCC.  In such cases, a stateful PCE could
   request to take control during the global optimization and return the
   delegation once done.

   Note that [RFC8231] specifies a mechanism for a PCC to delegate an
   orphaned LSP to another PCE.  The mechanism defined in this document
   can be used in conjunction to [RFC8231].  Ultimately, it is the PCC
   that decides which PCE to delegate the orphaned LSP to.

   This specification provides a simple extension: by using it a PCE can
   request control of one or more LSPs from any PCC over the stateful
   PCEP session.  The procedures for granting and relinquishing control
   of the LSPs are specified in accordance with the specification
   [RFC8231] unless explicitly set aside in this document.




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2.  Terminology

   This document uses the following terms defined in [RFC5440]:

     PCC:  Path Computation Client.

     PCE:  Path Computation Element.

     PCEP:  Path Computation Element communication Protocol.

   This document uses the following terms defined in [RFC8231]:

     PCRpt:  Path Computation State Report message.

     PCUpd:  Path Computation Update Request message.

     PLSP-ID:  A PCEP-specific identifier for the LSP.

     SRP:  Stateful PCE Request Parameters.

   Readers of this document are expected to have some familiarity with
   [RFC8231].

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  LSP Control Request Flag

   The Stateful PCE Request Parameters (SRP) object is defined in
   Section 7.2 of [RFC8231] and it includes a Flags field.

   A new flag, the "LSP-Control Request Flag" (C) - TBD, is introduced
   in the SRP object.  On a PCUpd message, a PCE sets the C Flag to 1 to
   indicate that it wishes to gain control of LSPs.  The LSPs are
   identified by the PLSP-ID in the LSP object following the SRP object.
   A PLSP-ID of value other than 0 and 0xFFFFF is used to identify the
   LSP for which the PCE requests control.  The PLSP-ID value of 0
   indicates that the PCE is requesting control of all LSPs originating
   from the PCC that it wishes to delegate.  The C Flag has no meaning
   in other PCEP messages that carry SRP objects and for which the C
   flag MUST be set to 0 on transmission and MUST be ignored on receipt.





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4.  Operation

   During normal operation, a PCC that wishes to delegate the control of
   an LSP sets the D Flag (delegate, Section 7.3 of [RFC8231]) to 1 in
   all PCRpt messages pertaining to the LSP.  The PCE confirms the
   delegation by setting D Flag to 1 in all PCUpd messages pertaining to
   the LSP.  The PCC revokes the control of the LSP from the PCE by
   setting D Flag to 0 in PCRpt messages pertaining to the LSP.  If the
   PCE wishes to relinquish the control of the LSP, it sets D Flag to 0
   in all PCUpd messages pertaining to the LSP.

   If a PCE wishes to gain control over an LSP, it sends a PCUpd message
   with C Flag set to 1 in SRP object.  The LSP for which the PCE
   requests control is identified by the PLSP-ID in the associated LSP
   object.  The PLSP-ID of 0 indicates that the PCE wants control over
   all LSPs originating from the PCC.  An implementation of this feature
   needs to make sure to check for the LSP control feature (C flag set
   to 1) before any check for PLSP-ID (as prescribed in [RFC8231]).  The
   D Flag and C Flag are mutually exclusive in a PCUpd message.  The PCE
   MUST NOT send a control request for the LSP which is already
   delegated to the PCE, i.e. if the D Flag is set in the PCUpd message,
   then the C Flag MUST NOT be set.  If a PCC receives a PCUpd message
   with D Flag set in the LSP object (i.e.  LSP is already delegated)
   and the C Flag is also set (i.e.  PCE is making a control request),
   the PCC MUST ignore the C Flag.  A PCC can decide to delegate the
   control of the LSP at its own discretion.  If the PCC grants or
   denies the control, it sends a PCRpt message with D Flag set to 1 and
   0 respectively in accordance with stateful PCEP [RFC8231].  If the
   PCC does not grant the control, it MAY choose to not respond, and the
   PCE MAY choose to retry requesting the control preferably using
   exponentially increasing timer.  Note that, if the PCUpd message with
   C Flag set is received for a currently non-delegated LSP (for which
   the PCE is requesting delegation), this MUST NOT trigger the error
   handling as specified in [RFC8231] (a PCErr with Error-type=19
   (Invalid Operation) and error-value 1 (Attempted LSP Update Request
   for a non-delegated LSP)).

   As per [RFC8231], a PCC cannot delegate an LSP to more than one PCE
   at any time.  If a PCE requests control of an LSP that has already
   been delegated by the PCC to another PCE, the PCC MAY ignore the
   request, or MAY revoke the delegation to the first PCE before
   delegating it to the second.  This choice is a matter of local
   policy.

   It should be noted that a legacy implementation of PCC that does not
   support this extension would receive an LSP control request: PCUpd
   message with C flag set and D flag (delegate) unset, it would ignore
   the C flag and trigger the error condition for the D flag as



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   specified in [RFC8231] (a PCErr with Error-type=19 (Invalid
   Operation) and error-value 1 (Attempted LSP Update Request for a non-
   delegated LSP)).  Further, in case of PLSP-ID of 0, the error
   condition as specified in [RFC8231] (a PCErr with Error-type=19
   (Invalid Operation) and error-value 3 (Attempted LSP Update Request
   for an LSP identified by an unknown PSP-ID)) would be triggered.

   [RFC8281] describes the setup, maintenance and teardown of PCE-
   initiated LSPs under the stateful PCE model.  It also specifies how a
   PCE may obtain control over an orphaned LSP that was PCE-initiated.
   A PCE implementation can apply the mechanism described in this
   document in conjunction with those in [RFC8281].

5.  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".

5.1.  Huawei's Proof of Concept based on ONOS

   The PCE function was developed in the ONOS open source platform.
   This extension was implemented on a private version as a proof of
   concept to enable multi-instance support.

   o  Organization: Huawei

   o  Implementation: Huawei's PoC based on ONOS




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   o  Description: PCEP as a southbound plugin was added to ONOS.  To
      support multi-instance ONOS deployment in a cluster, this
      extension in PCEP is used.  Refer
      https://wiki.onosproject.org/display/ONOS/PCEP+Protocol

   o  Maturity Level: Prototype

   o  Coverage: Full

   o  Contact: satishk@huawei.com

6.  Security Considerations

   The security considerations listed in [RFC8231] and [RFC8281] apply
   to this document as well.  However, this document also introduces a
   new attack vector.  An attacker may flood the PCC with request to
   delegate all of its LSPs at a rate which exceeds the PCC's ability to
   process them, either by spoofing messages or by compromising the PCE
   itself.  The PCC SHOULD be configured with a threshold rate for the
   delegation requests received from the PCE.  If the threshold is
   reached, it is RECOMMENDED to log the issue.

   A PCC is the ultimate arbiter of delegation.  As per [RFC8231], a
   local policy at PCC is used to influence the delegation.  A PCC can
   also revoke the delegation at any time.  A PCC need not blindly trust
   the control requests and SHOULD take local policy and other factors
   into consideration before honoring the request.

   Note that, a PCE may not be sure if a PCC supports this feature.  A
   PCE would try sending a control request to a 'legacy' PCC, which
   would in turn respond with an error as described in Section 4.  So a
   PCE would learn this fact only when it wants to take control over an
   LSP.  A PCE might also be susceptible to a downgrade attacks by
   falsifying the error condition.

   As per [RFC8231], it is RECOMMENDED that these PCEP extensions only
   be activated on authenticated and encrypted sessions across PCEs and
   PCCs belonging to the same administrative authority, using Transport
   Layer Security (TLS) [RFC8253], as per the recommendations and best
   current practices in BCP 195 [RFC7525] (unless explicitly excluded in
   [RFC8253]).

7.  IANA Considerations








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7.1.  SRP Object Flags

   IANA maintains a registry called the "Path Computation Element
   Protocol (PCEP) Numbers" registry.  It contains a subregistry called
   the "SRP Object Flag Field" registry.  This document requests IANA to
   allocate following code point in the "SRP Object Flag Field"
   subregistry.

           Bit            Description              Reference
           TBD            LSP-Control Request Flag This document

8.  Manageability Considerations

   All manageability requirements and considerations listed in [RFC5440]
   and [RFC8231] apply to PCEP protocol extensions defined in this
   document.  In addition, requirements and considerations listed in
   this section apply.

8.1.  Control of Function and Policy

   A PCC implementation SHOULD allow the operator to configure the
   policy based on which it honors the request to control the LSPs.
   This includes the handling of the case where an LSP control request
   is received for an LSP that is currently delegated to some other PCE.
   A PCC implementation SHOULD also allow the operator to configure the
   threshold rate based on which it accepts the delegation requests from
   the PCE.  Further, the operator MAY be allowed to trigger the LSP
   control request for a particular LSP at the PCE.  A PCE
   implementation SHOULD also allow the operator to configure an
   exponentially increasing timer to retry the control requests for
   which the PCE did not get a response.

8.2.  Information and Data Models

   The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
   include mechanism to trigger the LSP control request.

8.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

8.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440] and [RFC8231].



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8.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.

8.6.  Impact On Network Operations

   Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP
   extensions defined in this document.  Further, the mechanism
   described in this document can help the operator to request control
   of the LSPs at a particular PCE.

9.  Acknowledgements

   Thanks to Jonathan Hardwick to remind the authors to not use
   suggested values in IANA section.

   Thanks to Adrian Farrel, Haomian Zheng and Tomonori Takeda for their
   valuable comments.

   Thanks to Shawn M.  Emery for security directorate's review.

   Thanks to Francesca Palombini for GENART review.

   Thanks to Benjamin Kaduk, Martin Vigoureux, Alvaro Retana, and Barry
   Leiba for IESG reviews.

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>.







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   [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>.

10.2.  Informative References

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [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>.

   [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>.

   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/info/rfc8051>.

   [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-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", draft-ietf-pce-pcep-
              yang-12 (work in progress), July 2019.





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Appendix A.  Contributor Addresses

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

   EMail: dhruv.ietf@gmail.com


   Jon Parker
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   EMail: jdparker@cisco.com


   Chaitanya Yadlapalli
   AT&T
   200 S Laurel Aevenue
   Middletown NJ 07748
   USA

   EMail: cy098d@att.com

Authors' Addresses

   Aswatnarayan Raghuram
   AT&T
   200 S Laurel Aevenue
   Middletown, NJ  07748
   USA

   EMail: ar2521@att.com


   Al Goddard
   AT&T
   200 S Laurel Aevenue
   Middletown, NJ  07748
   USA

   EMail: ag6941@att.com





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   Jay Karthik
   Cisco Systems, Inc.
   125 High Street
   Boston, Massachusetts  02110
   USA

   EMail: jakarthi@cisco.com


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

   EMail: msiva@cisco.com


   Mahendra Singh Negi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: mahend.ietf@gmail.com


























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