PCE Working Group                                             Young Lee
                                                            Dhruv Dhody
Internet Draft                                                   Huawei
Intended Status: Standard
Expires: June 27, 2018                               Daniele Ceccarelli
                                                               Ericsson




                                                      December 27, 2017



      PCEP Extensions for Stitching LSPs in Hierarchical Stateful PCE
                                   Model



                  draft-lee-pce-lsp-stitching-hpce-01.txt


Abstract

   This document extends the Path Communication Element Communication
   Protocol (PCEP) to coordinate an end-to-end inter-domain tunnel
   setup over a multi-domain networks in the context of Hierarchical
   Stateful PCE environments.  This document uses Stitching Label (SL)
   to stich per-domain LSPs.



Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   http://www.ietf.org/ietf/1id-abstracts.txt




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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire June 27, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   warranty as described in the Simplified BSD License.

Table of Contents


   1. Introduction...................................................2
   2. Network Settings and concepts..................................4
      2.1. Stateful H-PCE Stitching Procedure........................6
      2.2. Applicability to ACTN....................................10
   3. Security Considerations.......................................10
   4. IANA Considerations...........................................10
   5. References....................................................11
      5.1. Normative References.....................................11
      5.2. Informative References...................................11
   Appendix A. Contributor Addresses................................14
   Author's Addresses...............................................14

1. Introduction

   In Multiprotocol Label Switching (MPLS) and Generalized MPLS
   (GMPLS), a Traffic Engineering Database (TED) is used in computing
   paths for connection oriented packet services and for circuits. The
   TED contains all relevant information that a Path Computation
   Element (PCE) needs to perform its computations. It is important
   that the TED should be complete and accurate anytime so that the PCE
   can perform path computations.

   In MPLS and GMPLS networks, Interior Gateway routing Protocols
   (IGPs) have been used to create and maintain a copy of the TED at


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   each node. One of the benefits of the PCE architecture [RFC4655] is
   the use of computationally more sophisticated path computation
   algorithms and the realization that these may need enhanced
   processing power not necessarily available at each node
   participating in an IGP.

   [Stateful-PCE] describes a set of extensions to PCEP to provide
   stateful control.  A stateful PCE has access to not only the
   information carried by the network's Interior Gateway Protocol
   (IGP), but also the set of active paths and their reserved resources
   for its computations. PCC can delegate the rights to modify the LSP
   parameters to an Active Stateful PCE.

   [RFC6805] describes a Hierarchical PCE (H-PCE) architecture which
   can be used for computing end-to-end paths for inter-domain MPLS
   Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs).
   Within the Hierarchical PCE (H-PCE) architecture [RFC6805], the
   Parent PCE (P-PCE) is used to compute a multi-domain path based on
   the domain connectivity information.  A Child PCE (C-PCE) may be
   responsible for a single domain or multiple domains, it is used to
   compute the intra-domain path based on its domain topology
   information.

   [Stateful H-PCE] presents general considerations for stateful PCE(s)
   in hierarchical PCE architecture. In particular, the behavior
   changes and additions to the existing stateful PCE mechanisms
   (including PCE-initiated LSP setup and active PCE usage) in the
   context of networks using the H-PCE architecture. Section 3.3.1 of
   [Stateful H-PCE] describe the per domain stitched LSP mode, where
   the individual per domain LSP are stitched together.

   [PCE-CC] introduces the architecture for PCE as a central
   controller, and examines the motivations and applicability for PCEP
   as a southbound interface. Section 2.1.3 describes the approach with
   hierarchical controllers.

   [BRPC-Stitch] describes how inter-domain labels over the inter-
   domain interfaces are determined in the multi-domain BRPC-based PCE
   environments. Further, the document introduces the concept of
   Stitching Label (SL) and Inter-domain Path Setup Type [PST]. This
   document also uses these concepts in the hierarchical Stateful PCE
   model.

   This document extends the Path Communication Element Communication
   Protocol (PCEP) to coordinate an end-to-end tunnel for a virtual
   network over multi-domain networks in the context of Hierarchical
   Stateful PCE environments.


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2. Network Settings and concepts

   This section describes network settings for this draft. Figure 1
   shows the context of Hierarchical Stateful PCE architecture where
   multi-domain LSP stitching is required for an end-to-end tunnel
   associated with a VN member.

                                     +-----------+
                                     +  Parent   +
                                     +   PCE     +
                                     +-----------+
                                   .       .      .
                                 .         .        .
                               .           .          .
                             .             .            .
      Stateful     +-----+  .          +-----+             +-----+
      C-PCE for    + PCE +             + PCE +             + PCE +
      Domain A     +-----+    Domain B +-----+    Domain C +-----+
                      .                    .                   .
                      .                    .                   .
                      .                    .                   .
                      .                    .                   .
                      .                    .                   .
                     ___                  ___                  ___
                    (   )                (   )                (   )
                   (  o  )              (  o  )              ( o--o)
                  (  / \  )            (   |\  )            (  |  | )
       EP1-------(o-o---o-o)==========(o-o-o-o-o)==========(o--o--o-o)--------EP2
                  |( \ / )|            |( \ / )|            |( | / )|
                  |(  o  )|            |(  o  )|            |( o-o )|
                  | (___) |            | (___) |            | (___) |
                  |       |            |       |            |       |
                  |Domain |Inter-domain|Domain |Inter-domain|Domain |
                  |   A   |    A-B     |   B   |    B-C     |   C   |
                  |<----->|<---------->|<----->|<---------->|<------>

                                       E2E Tunnel
                   <------------------------------------------------>



            Figure 1: Multi-domain LSP stitching for an end-to-end tunnel


   The draft provides PCE mechanisms to identify and isolate an end-to-
   end tunnel for a virtual network by concatenating a set of
   LSP/tunnel segments comprising an end-to-end tunnel. From Figure 1,
   there are a set of segments comprising an end-to-end tunnel: Per



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   Domain LSP A, Inter-domain Link A-B, Per Domain LSP B, Inter-domain
   Link B-C, and Per Domain C.

   It is important to realize that this end-to-end tunnel for a virtual
   network should be identifiable from other tunnels in the networks so
   as to guarantee its performance objective associated with this
   particular tunnel. See Section 2.2 for ACTN applicability for
   detailed discussion on this aspect.

   As per [BRPC-Stitch], Stitching Label (SL) is defined as a dedicated
   label that is used to stitch two tunnels (RSVP-TE tunnels or Segment
   Routing paths). This label is exchanged between exit BN(i) and entry
   BN(i+1) via PCEP. In case of H-PCE, the SL is conveyed from entry
   BN(i+1) to the child PCE(i+1) to the parent PCE, and then to child
   PCE(i) to the entry BN(i). The exit BN(i) learns the SL via the per-
   domain LSp setup technique (RSVP-TE, SR, PCECC etc).

   [BRPC-Stitch] define new LSP setup types for BRPC mode, this
   document also uses the same LSP setup type for the Stateful H-PCE
   mode.

      o  TBD1: Inter-Domain Traffic engineering end-to-end path is
   setup using H-PCE method.  This new LSP-TYPE value MUST be set in a
   PCInitiate messages sends by a P-PCE (Parent PCE) to its C-PCE
   (child PCE) of transit and destination domains to initiate a new
   inter-domain LSP tunnel.  In turn, the C-PCE MUST return a Stitching
   Label SL in the RRO of the PCRpt message to P-PCE.



      o  TBD2: Inter-Domain Traffic engineering local path is setup
   using RSVP-TE.  This new LSP-TYPE value MUST be set in the
   PCInitiate message sends by a C-PCE(i) requesting to a PCC of
   domain(i) to initiate a new local LSP tunnel(i) which is part of an
   inter-domain LSP tunnel.  This LSP-TYPE value MUST be used by the C-
   PCE(i) only after receiving a PCInitiate message with an LSP-TYPE
   equal to TBD1 from a P-PCE.  In turn, the PCC of domain(i) MUST
   return a Stitching Label SL in the RRO of the PCRpt message.



      o  TBD3: Inter-Domain Traffic engineering local path is setup
   using Segment Routing (SR).  This new LSP-TYPE value MUST be set in
   the PCInitiate message sends by a C-PCE(i) requesting to a PCC of
   domain(i) to initiate a new Segment Routing path which is part of
   an inter-domain Segment Routing path.  This LSP-TYPE value MUST be
   used by the C-PCE(i) only after receiving a PCInitiate message with


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   an LSP-TYPE equal to TBD1 from a P-PCE.  In turn, the PCC MUST
   return a Stitching Label SL in the RRO of the PCRpt message.

   [Editor's Note - This draft authors plan to discuss with authors of
   [BRPC-Stitch] to simplify this, as any new path setup type like
   PCECC would require another path-setup type to be defined here.]

   Thus, these LSP-TYPE value MUST be set in PCEP messages sends by a
   Parent PCE to child PCE as well as between child PCE and the PCCs
   when SL is used.



               2.1. Stateful H-PCE Stitching Procedure

   Taking the sample hierarchical domain topology example from
   [RFC6805] as the reference topology for the entirety of this
   document.

         -----------------------------------------------------------------
        |   Domain 5                                                      |
        |                              -----                              |
        |                             |PCE 5|                             |
        |                              -----                              |
        |                                                                 |
        |    ----------------     ----------------     ----------------   |
        |   | Domain 1       |   | Domain 2       |   | Domain 3       |  |
        |   |                |   |                |   |                |  |
        |   |        -----   |   |        -----   |   |        -----   |  |
        |   |       |PCE 1|  |   |       |PCE 2|  |   |       |PCE 3|  |  |
        |   |        -----   |   |        -----   |   |        -----   |  |
        |   |                |   |                |   |                |  |
        |   |            ----|   |----        ----|   |----            |  |
        |   |           |BN11+---+BN21|      |BN23+---+BN31|           |  |
        |   |   -        ----|   |----        ----|   |----        -   |  |
        |   |  |S|           |   |                |   |           |D|  |  |
        |   |   -        ----|   |----        ----|   |----        -   |  |
        |   |           |BN12+---+BN22|      |BN24+---+BN32|           |  |
        |   |            ----|   |----        ----|   |----            |  |
        |   |                |   |                |   |                |  |
        |   |         ----   |   |                |   |   ----         |  |
        |   |        |BN13|  |   |                |   |  |BN33|        |  |
        |    -----------+----     ----------------     ----+-----------   |
        |                \                                /               |
        |                 \       ----------------       /                |
        |                  \     |                |     /                 |
        |                   \    |----        ----|    /                  |
        |                    ----+BN41|      |BN42+----                   |


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        |                        |----        ----|                       |
        |                        |                |                       |
        |                        |        -----   |                       |
        |                        |       |PCE 4|  |                       |
        |                        |        -----   |                       |
        |                        |                |                       |
        |                        | Domain 4       |                       |
        |                         ----------------                        |
        |                                                                 |
         -----------------------------------------------------------------


   Section 3.3.1 of [Stateful H-PCE] describes the per-domain stitched
   LSP mode and list all the steps needed. To support SL based
   stitching, the steps are modified as follows -

   Using the reference architecture described in Figure above:

   (1)  The P-PCE (PCE5) is requested to initiate a LSP.

   Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to
   determine the end to end path, which are broken into per-domain LSPs
   say -



      o  S-BN41

      o  BN41-BN33

      o  BN33-D



   For LSP (BN33-D)



   (2)  The P-PCE (PCE5) sends the initiate request to the child PCE
   (PCE3) via PCInitiate message for LSP (BN33-D) with ERO=(BN33..D)
   and LSP-TYPE=TBD1.

   (3)  The PCE3 further propagates the initiate message to BN33 with
   the ERO and LSP-TYPE=TBD2/TBD3 based on setup type.

   (4)  BN33 initiates the setup of the LSP as per the path and reports
   to the PCE3 the LSP status ("GOING-UP").


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   (5)  The PCE3 further reports the status of the LSP to the P-PCE
   (PCE5).

   (6)  The node BN33 notifies the LSP state to PCE3 when the state is
   "UP" it also carry the stitching label (SL33) in RRO as
   (SL33,BN33..D).

   (7)  The PCE3 further reports the status of the LSP to the P-PCE
   (PCE5) as well as carry the stitching label (SL33) in RRO as
   (SL33,BN33..D).



   For LSP (BN41-BN33)



   (8)  The P-PCE (PCE5) sends the initiate request to the child PCE
   (PCE4) via PCInitiate message for LSP (BN41-BN33) with
   ERO=(BN41..BN42,SL33,BN33) and LSP-TYPE=TBD1.



   (9)  The PCE4 further propagates the initiate message to BN41 with
   the ERO and LSP-TYPE=TBD2/TBD3 based on setup type. In case of
   RSVP_TE, the node BN41 encode the stitching label SL33 as part of
   the ERO to make sure the node BN42 uses the label SL33 towards node
   BN33. In case of SR, the label SL33 is part of the label stack
   pushed at node BN41.



   (10) BN41 initiates the setup of the LSP as per the path and reports
   to the PCE4 the LSP status ("GOING-UP").



   (11) The PCE4 further reports the status of the LSP to the P-PCE
   (PCE5).



   (l2) The node BN41 notifies the LSP state to PCE4 when the state is
   "UP" it also carry the stitching label (SL41) in RRO as
   (SL41,BN41..BN33).




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   (13) The PCE4 further reports the status of the LSP to the P-PCE
   (PCE5) as well as carry the stitching label (SL41) in RRO as
   (SL41,BN41..BN33).



   For LSP (S-BN41)



   (14)  The P-PCE (PCE5) sends the initiate request to the child PCE
   (PCE1) via PCInitiate message for LSP (S-BN41) with
   ERO=(S..BN13,SL41,BN41).



   (15)  The PCE1 further propagates the initiate message to node S
   with the ERO. In case of RSVP_TE, the node S encode the stitching
   label SL41 as part of the ERO to make sure the node BN13 uses the
   label SL41 towards node BN41. In case of SR, the label SL41 is part
   of the label stack pushed at node S.



   (16)  S initiates the setup of the LSP as per the path and reports
   to the PCE1 the LSP status ("GOING-UP").



   (17)  The PCE1 further reports the status of the LSP to the P-PCE
   (PCE5).



   (18)  The node S notifies the LSP state to PCE1 when the state
   is"UP".



   (19)  The PCE1 further reports the status of the LSP to the P-PCE
   (PCE5).



   In this way, per-domain LSP are stitched together using the
   stitching label (SL). The per-domain LSP MUST be setup from the
   destination domain towards the source domain one after the other.


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   Once the per-domain LSP is setup, the entry BN chooses a free label
   for the Stitching Label SL and add a new entry in its MPLS LFIB with
   this SL label. The SL from the destination domain is propagated to
   adjacent transit domain, towards the source domain at each step.
   This happens through the entry BN to C-PCE to the P-PCE and vice-
   versa. In case of RSVP-TE, the entry BN further propagates the SL
   label to the exit BN via RSVP-TE. In case of SR, the SL label is
   pushed as part of the SR label stack.



2.2. Applicability to ACTN

   [ACTN] describes framework for Abstraction and Control of TE
   Networks (ACTN), where each Physical Network Controller (PNC) is
   equivalent to C-PCE and P-PCE is the Multi-Domain Service
   Coordinator (MDSC).  The Per domain stitched LSP as per the
   Hierarchical PCE architecture described in Section 3.3.1 and Section
   4.1 of [Stateful H-PCE] is well suited for ACTN.

   The stitching label (SL) mechanism as described in this document is
   well suited for ACTN when per domain LSP needs to be stitched to
   form an E2E tunnel or a VN Member. It is to be noted that certain
   VNs require isolation from other clients. The stitching label
   mechanism described in this document can be applicable to the VN
   isolation use-case by uniquely identifying the concatenated
   stitching labels across multi-domain only to a certain VN member or
   an E2E tunnel.




3. Security Considerations

   Procedures and protocol extensions defined in this document do not
   effect the overall PCEP security model.  See [RFC5440], [I-D.ietf-
   pce-pceps]. It is suggested that any mechanism used for securing the
   transmission of other PCEP message be applied here as well.  As a
   general precaution, it is RECOMMENDED that these PCEP extensions
   only be activated on authenticated and encrypted sessions belonging
   to the same administrative authority.

4. IANA Considerations

   This document requests IANA actions to allocate code points for the
   protocol elements defined in this document.



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5. References

               5.1. Normative References

   [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
             Computation Element (PCE)-Based Architecture", RFC 4655,
             August 2006.

   [RFC4674] Le Roux, J., Ed., "Requirements for Path Computation
             Element (PCE) Discovery", RFC 4674, October 2006.

   [RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
             Zhang, "OSPF Protocol Extensions for Path Computation
             Element (PCE) Discovery", RFC 5088, January 2008.

   [RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
             Zhang, "IS-IS Protocol Extensions for Path Computation
             Element (PCE) Discovery", RFC 5089, January 2008.

   [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
             OSPF Opaque LSA Option", RFC 5250, July 2008.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
             Engineering", RFC 5305, October 2008.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
             Element (PCE) Communication Protocol (PCEP)", RFC 5440,
             March 2009.



               5.2. Informative References

   [JMS]    Java Message Service, Version 1.1, April 2002, Sun
             Microsystems.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic
             Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
             September 2003.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4203, October 2005.




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   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
             Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [BGP-LS] Gredler, H., Medved, J., Previdi, S., Farrel, A., and
             S.Ray, "North-Bound Distribution of Link-State and TE
             information using BGP", draft-ietf-idr-ls-distribution,
             work in progress.

   [S-PCE-GMPLS] X. Zhang, et. al, "Path Computation Element (PCE)
             Protocol Extensions for Stateful PCE Usage in GMPLS-
             controlled Networks", draft-ietf-pce-pcep-stateful-pce-
             gmpls, work in progress.

   [RFC7399] A. Farrel and D. king, "Unanswered Questions in the Path
             Computation Element Architecture", RFC 7399, October 2015.

   [RFC7449]  Y. Lee, G. Bernstein, "Path Computation Element
             Communication Protocol (PCEP) Requirements for Wavelength
             Switched Optical Network (WSON) Routing and Wavelength
             Assignment", RFC 7449, February 2015.

   [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
             Reflection: An Alternative to Full Mesh Internal BGP
             (IBGP)", RFC 4456, April 2006.

   [RFC6163]  Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS
             and PCE Control of Wavelength Switched Optical Networks",
             RFC 6163,

   [G.680] ITU-T Recommendation G.680, Physical transfer functions of
             optical network elements, July 2007.

   [ACTN-Frame] D.Ceccarelli, and Y. Lee (Editors), "Framework for
             Abstraction and Control of TE Networks", draft-ietf-teas-
             actn-framework, work in progress.

   [RFC6805] A. Farrel and D. King, "The Application of the Path
             Computation Element Architecture to the Determination of a
             Sequence of Domains in MPLS and GMPLS", RFC 6805, November
             2012.

   [PCEP-LS-Arch] Y. Lee, D. Dhody and D. Ceccarelli, "Architecture and
             Requirement for Distribution of Link-State and TE
             Information via PCEP", draft-leedhody-teas-pcep-ls, work
             in progress.




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   [PCEP-LS] D. Dhody, Y. Lee and D. Ceccarelli "PCEP Extension for
             Distribution of Link-State and TE Information.", work in
             progress, September 21, 2015[Stateful-PCE] Crabbe, E.,
             Minei, I., Medved, J., and R. Varga, "PCEP Extensions for
             Stateful PCE", draft-ietf-pce-stateful-pce, work in
             progress.

   [PCE-Initiated] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga,
             "PCEP Extensions for PCE-initiated LSP Setup in a Stateful
             PCE Model", draft-ietf-pce-pce-initiated-lsp, work in
             progress.

   [Stateful H-PCE] D. Dhody, Y. Lee and D. Ceccarelli, "Hierarchical
             Stateful Path Computation Element (PCE)", draft-ietf-pce-
             stateful-hpce, work-in-progress.

   [FlexOSPF] X. Zhang, H. Zheng, R. Casellas, O. Gonzalez de Dios, D.
             Ceccarelli, "GMPLS OSPF Extensions in support of Flexi-
             grid DWDM networks", draft-ietf-ccamp-flexible-grid-ospf-
             ext-05, work in progress.

   [PST] Sivabalan, S., Medved, J., Minei, I., Crabbe, E., Varga,
             R., Tantsura, J., and J. Hardwick, "Conveying path setup
             type in PCEP messages", draft-ietf-pce-lsp-setup-type-03
             work in progress.
























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Appendix A. Contributor Addresses



Author's Addresses


   Young Lee
   Huawei Technologies
   5340 Legacy Drive, Building 3
   Plano, TX 75023, USA

   Email: leeyoung@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka 560066
   India
   Email: dhruv.ietf@gmail.com



   Daniele Ceccarelli
   Ericsson
   Torshamnsgatan,48
   Stockholm
   Sweden

   Email: daniele.ceccarelli@ericsson.com














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