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PCE Working Group                                           S. Sivabalan
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                              S. Previdi
Expires: October 25, 2015                            Cisco Systems, Inc.
                                                             J. Tantsura
                                                             J. Hardwick
                                                     Metaswitch Networks
                                                              M. Nanduri
                                                   Microsoft Corporation
                                                          April 23, 2015

        Carrying Binding Label/Segment-ID in PCE-based Networks.


   It is possible to associate a binding label to RSVP-TE signaled
   Traffic Engineering Label Switching Path or binding Segment-ID (SID)
   to Segment Routed Traffic Engineering path.  Such a binding label/SID
   can be used by an upstream node for steering traffic into the
   appropriate TE path to enforce TE policies.  This document proposes
   an approach for reporting binding label/SID to Path Computation
   Element (PCE) for supporting PCE-based Traffic Engineering policies.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 25, 2015.

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Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.  Path Binding TLV  . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   A PCE can compute Traffic Engineering paths (TE paths) through a
   network that are subject to various constraints.  Currently, TE paths
   are either set up using the RSVP-TE signaling protocol or Segment
   Routed (SR).  We refer to such paths as RSVP-TE paths and SR-TE paths
   respectively in this document.

   Similar to assigning label to a Forwarding Equivalence Class (FEC)
   via Label Distribution Protocol (LDP), a binding label can be
   assigned to a RSVP-TE LSP.  If the topmost label of an incoming
   packet is the binding label, the packet is steered onto the RSVP-TE
   LSP.  As such, any upstream node can use binding labels to steer the
   packets that it originates to appropriate TE LSPs to enforce TE
   policy.  Similarly, a binding SID (see
   [I-D.ietf-isis-segment-routing-extensions] and
   [I-D.ietf-ospf-segment-routing-extensions]) can be used to enforce TE
   policy with SR-TE path.  Note that if an SR-TE path is represented as
   a forwarding-adjacency, then the corresponding adjacency SID can be
   used as the binding SID.  In such case, the path is advertised using
   the routing protocols as described in [RFC5440].  The binding SID
   provides an alternate mechanism without additional overhead on
   routing protocols.

   [RFC5440] describes the Path Computation Element Protocol (PCEP) for
   communication between a Path Computation Client (PCC) and a PCE or
   between a pair of PCEs.[I-D.ietf-pce-stateful-pce] specifies
   extension to PCEP that allows a PCC to delegate its LSPs to a PCE.
   The PCE can then update the state of LSPs delegated to it.
   [I-D.ietf-pce-pce-initiated-lsp] specifies a mechanism allowing a PCE
   to dynamically instantiate an LSP on a PCC by sending the path and
   characteristics of the LSP.  The PCEP extension to setup and maintain
   SR-TE paths is specified in [I-D.ietf-pce-segment-routing].

   Binding label/SID has local significance to the ingress node of the
   corresponding TE path.  When a stateful PCE is deployed for setting
   up TE paths, it may be desirable to report the binding label or SID
   to the PCE for the purpose of enforcing end-to-end TE policy.  A
   sample Data Center (DC) use-case is illustrated in the following
   diagram.  In the MPLS DC network, an SR LSP (without traffic
   engineering) is established using a prefix SID advertised by BGP (see
   [I-D.keyupate-idr-bgp-prefix-sid]).  In IP/MPLS WAN, an SR-TE LSP is
   setup using the PCE.  The list of SIDs of the SR-TE LSP is {A, B, C,
   D}.  The gateway node 1 (which is the PCC) allocates a binding SID X
   and reports it to the PCE.  In order for the access node to steer the
   traffic over the SR-TE LSP, the PCE passes the SID stack {Y, X} where
   Y is the prefix SID of the gateway node-1 to the access node.  In the
   absence of the binding SID X, the PCE should pass the SID stack {Y,

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   A, B, C, D} to the access node.  This example also illustrates the
   additional benefit of using the binding SID to reduce the number of
   SIDs imposed on the access nodes with a limited forwarding capacity.

              SID stack
              {Y, X}              +-----+
       _ _ _ _ _ _ _ _ _ _ _ _ _ _| PCE |
      |                           +-----+
      |                              ^
      |                              | Binding
      |           .-----.            | SID (X)     .-----.
      |          (       )           |            (       )
      V       .--(         )--.      |        .--(         )--.
   +------+  (                 )  +-------+  (                 )  +-------+
   |Access|_(  MPLS DC Network  )_|Gateway|_(    IP/MPLS WAN    )_|Gateway|
   | Node | (  ==============>  ) |Node-1 | ( ================> ) |Node-2 |
   +------+  (     SR path     )  +-------+  (    SR-TE path   )  +-------+
              '--(         )--'    Prefix     '--(         )--'
                  (       )        SID of         (       )
                   '-----'         Node-1          '-----'
                                   is Y            SIDs for SR-TE LSP:
                                                   {A, B, C, D}

                Figure 1: A sample Use-case of Binding SID

   In this document, we introduce a new OPTIONAL TLV that a PCC can use
   in order to report the binding label associated with a TE LSP.  This
   TLV is intended for TE LSPs established using RSVP-TE, SR, or any
   other future method.  Also, in the case of SR-TE LSPs, the TLV can
   carry an MPLS label binding (for SR-TE path with MPLS data-plane) or
   a binding SID (e.g., IPv6 address for SR-TE paths with IPv6 data-
   plane).  However, use of this TLV for non-MPLS label binding will be
   described in separate document(s).

2.  Terminology

   The following terminologies are used in this document:

   LER:  Label Edge Router.

   LSP:  Label Switched Path.

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   LSR:  Label Switching Router.

   PCC:  Path Computation Client.

   PCE:  Path Computation Element

   PCEP:  Path Computation Element Protocol.

   SID:  Segment ID.

   SR:  Segment Routing.

   TLV:  Type, Length, and Value.

3.  Path Binding TLV

   The new optional TLV is called "TE-PATH-BINDING TLV" whose format is
   shown in the diagram below is defined to carry binding label or SID
   for a TE path.  This TLV is associated with the LSP object specified
   in ([I-D.ietf-pce-stateful-pce]).  The type of this TLV is to be
   allocated by IANA.

       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            |
      |        Binding Type (BT)      |          Binding Value        |
      ~            Binding Value (continued) (variable length)        ~

                       Figure 2: TE-PATH-BINDING TLV

   TE-PATH-BINDING TLV is a generic TLV such that it is able to carry
   MPLS label binding as well as other types of future bindings (e.g.,
   IPv6 SR path).  The one octet Binding Type (BT) field identifies the
   type of binding included in the TLV.  This document specifies the
   following BT value:

   o  BT = 0: MPLS label (default).

4.  Operation

   The binding value is allocated by PCC and reported to PCE via PCRpt
   message.  If a PCE does not recognize the TE-PATH-BINDING TLV, it

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   MUST ignore the TLV in accordance with ([RFC5440]).  If a PCE
   recognizes the TLV but does not support the TLV, it MUST send PCErr
   with Error-Type = 2 (Capability not supported).

   If a TE-PATH-BINDING TLV is absent in PCRpt message, PCE MUST assume
   that the corresponding LSP does not have any binding.  If there are
   more than one PATH-BINDING TLVs, only the first TLV MUST be processed
   and the rest MUST be silently ignored.  If PCE recognizes an invalid
   binding value (e.g., label value from the reserved label space when
   MPLS label binding is used), it MUST send the PCE error message with
   Error-Type = 10 ("Reception of an invalid object") and Error Value =
   TBD ("Bad label value") as specified in

   If a PCC receives TE-PATH-BINDING TLV in any message, it MUST close
   the corresponding PCEP session with the reason "Reception of a
   malformed PCEP message" according ([RFC5440]).  Similarly, if a PCE
   receives a TE-PATH-BINDING TLV in any message other than a PCRpt or
   if the TE-PATH-BINDING TLV is associated with any object other than
   LSP object, the PCE MUST close the corresponding PCEP session with
   the reason "Reception of a malformed PCEP message" according

   If a PCC wants to withdraw or modify a previously reported binding
   value, it MUST send a PCRpt message without any TE-PATH-BINDING TLV
   and with the TE-PATH-BINDING TLV containing the new binding value

5.  Security Considerations

   No additional security measure is required.

6.  IANA Considerations

   IANA is requested to allocate a new TLV type (recommended value is
   31)for TE-PATH-BINDING TLV specified in this document.

   This document requests that a registry is created to manage the value
   of the Binding Type field in the TE-PATH-BINDING TLV.

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      Value   Description           Reference

        0     MPLS Label            This document

7.  Acknowledgements

8.  Normative References

              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
              Extensions for Segment Routing",
              draft-ietf-isis-segment-routing-extensions-03 (work in
              progress), October 2014.

              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing",
              draft-ietf-ospf-segment-routing-extensions-04 (work in
              progress), February 2015.

              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-04 (work in
              progress), April 2015.

              Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
              Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick,
              "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-03 (work in progress),
              April 2015.

              Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
              Extensions for Stateful PCE",
              draft-ietf-pce-stateful-pce-11 (work in progress),
              April 2015.

              Patel, K., Ray, S., Previdi, S., and C. Filsfils, "Segment
              Routing Prefix SID extensions for BGP",
              draft-keyupate-idr-bgp-prefix-sid-01 (work in progress),
              April 2015.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.

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

Authors' Addresses

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

   Email: msiva@cisco.com

   Clarence Filsfils
   Cisco Systems, Inc.
   Pegasus Parc
   De kleetlaan 6a, DIEGEM  BRABANT 1831

   Email: cfilsfil@cisco.com

   Stefano Previdi
   Cisco Systems, Inc.
   Via Del Serafico, 200
   Rome, Rome  00142

   Email: sprevidi@cisco.com

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   Jeff Tantsura
   300 Holger Way
   San Jose, CA  95134

   Email: jeff.tantsura@ericsson.com

   Jonathan Hardwick
   Metaswitch Networks
   100 Church Street
   Enfield, Middlesex

   Email: Jonathan.Hardwick@metaswitch.com

   Mohan Nanduri
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052

   Email: mnanduri@microsoft.com

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