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PCE Working Group                                                  Q. Wu
Internet-Draft                                                  D. Dhody
Intended status: Standards Track                                  Huawei
Expires: December 29, 2017                                  M. Boucadair
                                                            C. Jacquenet
                                                                  Orange
                                                             J. Tantsura
                                                           June 27, 2017


          PCEP Extensions for Service Function Chaining (SFC)
                  draft-wu-pce-traffic-steering-sfc-12

Abstract

   This document provides an overview of the usage of Path Computation
   Element (PCE) to dynamically structure service function chains.
   Service Function Chaining (SFC) is a technique that is meant to
   facilitate the dynamic enforcement of differentiated traffic
   forwarding policies within a domain.  Service function chains are
   composed of an ordered set of elementary Service Functions (such as
   firewalls, load balancers) that need to be invoked according to the
   design of a given service.  Corresponding traffic is thus forwarded
   along a Service Function Path (SFP) that can be computed by means of
   PCE.

   This document specifies extensions to the Path Computation Element
   Protocol (PCEP) that allow a stateful PCE to compute and instantiate
   Service Function Paths.

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 http://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 December 29, 2017.





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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
   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
   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.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Service Function Paths and PCE  . . . . . . . . . . . . . . .   4
   4.  Overview of PCEP Operation in SFC-Enabled Networks  . . . . .   6
     4.1.  SFP Instantiation . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SFP Withdrawal  . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  SFP Delegation and Cleanup  . . . . . . . . . . . . . . .   7
     4.4.  SFP State Synchronization . . . . . . . . . . . . . . . .   7
     4.5.  SFP Update and Report . . . . . . . . . . . . . . . . . .   7
   5.  Object Formats  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  The LSP Object  . . . . . . . . . . . . . . . . . . . . .   8
       5.2.1.  SFP Identifiers TLV . . . . . . . . . . . . . . . . .   8
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   9
   7.  SFP Instantiation Signaling and Forwarding Considerations . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Service Function Chaining (SFC) enables the creation of composite
   services that consist of an ordered set of Service Functions (SF)
   that must be applied to packets and/or frames and/or flows selected
   as a result of service-inferred traffic classification as described
   in [RFC7665].  A Service Function Path (SFP) is a path along which
   traffic that is bound to a specific service function chain will be



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   forwarded.  Packets typically follow a Service Function Path from a
   classifier through the Service Functions (SF) that need to be invoked
   according to the SFC instructions.  Forwarding decisions are made by
   Service Function Forwarders (SFF) according to such instructions.

   [RFC5440] describes the Path Computation Element Protocol (PCEP) as
   the protocol used by a Path Computation Client (PCC) and a Path
   Control Element (PCE) to exchange information, thereby enabling the
   computation of Multiprotocol Label Switching (MPLS) for Traffic
   Engineering Label Switched Path (TE LSP), in particular.

   [I-D.ietf-pce-stateful-pce] specifies extensions to PCEP to enable a
   stateful control of MPLS TE LSPs.  [I-D.ietf-pce-pce-initiated-lsp]
   provides the extensions needed for stateful PCE-initiated LSP
   instantiation.

   This document specifies PCEP extensions that allow a stateful PCE to
   compute and instantiate traffic-engineered Service Function Paths
   (SFP).

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [RFC2119].

   This document makes use of these acronyms:

   PCC:  Path Computation Client.

   PCE:  Path Computation Element.

   PCEP:  Path Computation Element Protocol.

   PDP:  Policy Decision Point.

   SF:  Service Function.

   SFC:  Service Function Chain.

   SFP:  Service Function Path.

   RSP:  Rendered Service Path.

   SFF:  Service Function Forwarder.

   UNI:  User-Network Interface.




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3.  Service Function Paths and PCE

   Service function chains are constructed as a sequence of SFs, where a
   SF can be virtualized or embedded in a physical network element.  One
   or several SFs may be supported by the same physical network element.
   A SFC creates an abstracted view of a service and specifies the set
   of required SFs as well as the order in which they must be executed.

   When an SFC is created, it is necessary to select the specific
   instances of SFs that will be used.  A service function path for that
   SFC will then be established (notion of rendered service path) or can
   be precomputed, based upon the sequence of SFs that need to be
   invoked by the corresponding traffic, i.e., the traffic that is bound
   to the corresponding SFC.  Note that a SF instance can be serviced by
   one or multiple SFFs.  One or multiple SF instances can be serviced
   by one SFF.  Thus, the instantiation of an SFC results in the
   establishment of a Service Function Path, either in a hop-by-hop
   fashion, or by means of traffic-engineering capabilities.  In the
   latter case, the SFP is precomputed, i.e., an SFP is an instantiation
   of the defined SFC as described in [RFC7665].

   The computation, the selection, and the establishment of a traffic-
   engineered SFP can rely upon a set of (service-specific) policies
   (forwarding and routing, QoS, security, etc., or a combination
   thereof).  Stateful PCE with appropriate SFC-aware PCEP extensions
   can be used to compute traffic-engineered SFPs.

























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                       SFC Control Plane
                  +------------------------+
                  |PCE based Controller    |
            I2    | +-------++-------+     |
     +------------- |Policy || TE-DB |     |
     |      I1    | +-------++-------+     <----+
     | +----------|      +-------------+   |    |
     | |SFP       |      |LSP-DB/SFP-DB|   |    |I2
     | |Instan-   |      +-------------+   |    |
     | |tiation   +-----------^------------+    |policy-provisioning
     | |PCEP                  |                 |information/
     | |Signaling          I2 |                 |Carried by NETCONF,
     | |                      |                 |BGP, for example
     | |                      |                 |
     | |                      |                 |
     | |               +------V+           +----+--+
     V V               |       |           |       |
    +-----+  Forwarding|       | Forwarding|       | Forwarding
    | SFC |----------->| SFF-1 | --------->| SFF-2 |----------->
    Classifier         |       |           |       |
    |     |            |       |           |       |
    +-----+            ++-----++           +-----+-+
                        |     |                  |
                     +--+--+ ++----+          +--+--+
                     |SF-1 | |SF-2 |          |SF-3 |
                     |     | |     |          |     |
                     +--+--+ +---+-+          +--+--+
                        |I2      |I2             |I2
                        V        V               V

                   Figure 1: PCE-based SFP instantiation

   In Figure 1, the PCE-based Controller [I-D.ietf-teas-pce-central-
   control] in the SFC Control plane is responsible for computing the
   path for a given service function chain.  This PCE-based controller
   can operate as a stateful PCE ([I-D.draft_ietf-stateful-pce]) that
   will provide a classifier (a headend from a PCE standpoint) with the
   PCEP-formatted information to instantiate a given SFP.  As a
   consequence, the PCE-based controller derives the set of policy-
   provisioning information (namely SFP configuration information and
   traffic classification rules) that will be provided to the various
   elements (Classifier, SFF) involved in the establishment of the SFP.

   By doing so, SFC Classifier can bind a flow to a service function
   chain and forward such flow along the corresponding SFP.  The SFC
   Control Plane [I-D.ietf-sfc-control-plane] is also responsible for
   defining the appropriate policies (traffic classification, forwarding
   and routing, etc.) that will be enforced by SFC Classifiers,SFF Nodes



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   and SF Nodes, as described in [RFC7665].  From that standpoint, the
   SFC Control Plane embeds a Policy Decision Point that is responsible
   for defining the SFC policies.  SFC policies will be provided by the
   PDP and enforced by SFC components like classifiers and SFFs by means
   of policy-provision information.  A protocol like NETCONF, BGP can be
   used to carry such policy-provisioning information.

4.  Overview of PCEP Operation in SFC-Enabled Networks

   A PCEP speaker indicates its ability to support PCE-computed SFP
   paths during the PCEP Initialization phase via a mechanism described
   in Section 5.1.  A PCE may initiate SFPs only for PCCs that
   advertised this capability; a PCC follows the procedures described in
   this document only for sessions where the PCE advertised this
   capability.

   As per Section 5.1 of [I-D.ietf-pce-pce-initiated-lsp], the PCE sends
   a Path Computation LSP Initiate Request (PCInitiate) message to the
   PCC to instantiate or delete a LSP.  The Explicit Route Object (ERO)
   is used to encode either a full sequence of SF instances or a
   specific sequence of SFFs and SFs to establish an SFP.  If the said
   SFFs and SFs are identified with an IP address, the IP sub-object can
   be used as a SF/SFF identification means.  This document makes no
   change to the PCInitiate message format but extends LSP objects
   described in Section 5.2.

   Editor's note: In case a PCE-Initiated signaling mechanism is used to
   set up the service function path, does the classifier / PCE-Initiated
   signaling protocol need to understand whether an IP address is
   assigned to a SFF or a SF, or the signaling protocol is only used to
   signal IP addresses for SFs?

   To prevent multiple classifiers assign the same SFP ID to one Service
   Function Path(SFP ID assignment conflict),in this document, we assume
   SFP ID can be predetermined and assigned by stateful PCE when
   stateful PCE can be used to compute traffic-engineered SFPs.

4.1.  SFP Instantiation

   The instantiation of a SFP is the same as defined in Section 5.3 of
   [I-D.ietf-pce-pce-initiated-lsp].  Rules for processing and error
   codes remain unchanged.

4.2.  SFP Withdrawal

   The withdrawal of an SFP is the same as defined in Section 5.4 of
   [I-D.ietf-pce-pce-initiated-lsp]: the PCE sends an LSP Initiate
   Message with an LSP object carrying the PLSP-ID of the SFP and the



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   SFP Identifier to be removed, as well as an SRP object with the R
   flag set (LSP-REMOVE as per Section 5.2 of
   [I-D.ietf-pce-pce-initiated-lsp]).  Rules for processing and error
   codes remain unchanged.

4.3.  SFP Delegation and Cleanup

   SFP delegation and cleanup operations are similar to those defined in
   Section 6 of [I-D.ietf-pce-pce-initiated-lsp].  Rules for processing
   and error codes remain unchanged.

4.4.  SFP State Synchronization

   State Synchronization operations described in Section 5.4 of
   [I-D.ietf-pce-stateful-pce] can be applied to SFP state maintenance
   as well.

4.5.  SFP Update and Report

   A PCE can send an SFP Update request to a PCC to update one or more
   attributes of an SFP and to re-signal the SFP with the updated
   attributes.  A PCC can send an SFP state report to a PCE, and which
   contains the SFP State information.  The mechanism is described in
   [I-D.ietf-pce-stateful-pce] and can be applied to SFPs as well.

5.  Object Formats

5.1.  The OPEN Object

   The optional TLV shown in Figure 2 is defined for use in the OPEN
   Object to indicate the PCEP speaker's Service Function Chaining
   capability.

   The SFC-PCE-CAPABILITY TLV is an optional TLV to be carried in the
   OPEN Object to advertise the SFC capability during the PCEP session.

    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=TBD           |            length=4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Reserved           |             Flags             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       SFC-PCE-CAPABILITY TLV Format

   The code point for the TLV type is to be defined by IANA (see
   Section 9).  The TLV length is 4 octets.



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   As per [I-D.ietf-pce-stateful-pce], a PCEP speaker advertises the
   capability of instantiating PCE-initiated LSPs via the Stateful PCE
   Capability TLV (LSP-INSTANTIATION-CAPABILITY bit) carried in an Open
   message.  The inclusion of the SFC-PCE-CAPABILITY TLV in an OPEN
   object indicates that the sender is SFC-capable.  Both mechanisms
   indicate the SFP instantiation capability of the PCEP speaker.

5.2.  The LSP Object

   The LSP object is defined in [I-D.ietf-pce-pce-initiated-lsp] and
   included here for reference (Figure 3).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                PLSP-ID                | Flags |F|C|  O|A|R|S|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                        TLVs                                 //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             LSP Object Format

   A new flag, called the SFC flag (F-bit), is introduced.  The F-bit
   set to "1" indicates that this LSP is actually an SFP.  The C flag
   will also be set to indicate it was created via a PCInitiate message.

5.2.1.  SFP Identifiers TLV

   As described in section 4, SFP ID is predetermined and assigned by
   stateful PCE.  The SFP Identifiers TLV MUST be included in the LSP
   object for SFPs.  The SFP Identifier TLV is used by the classifier to
   select the SFP along which some traffic will be forwarded, according
   to the traffic classification rules applied by the classifier
   [RFC7665].  The SFP Identifier is part of the SFC metadata carried in
   packets and is used by the SFF to invoke service functions and
   identify the next SFF.

   The format of the SFP Identifier TLV is shown in Figure 4.












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      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path ID                      | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Service Path ID (SPI): 24 bits
      Service Index (SI): 8 bits

                                 Figure 4

   SPI: identifies a service path.  The same ID is used by the
   participating nodes for path setup/selection.  An administrator can
   use the SPI for reporting and troubleshooting packets along a
   specific path.  SPI along with PLSP-ID is used by PCEP to identify
   the Service Path.

   SI: provides location within the service path.

6.  Backward Compatibility

   The SFP instantiation capability defined as a PCEP extension and
   documented in this draft MUST NOT be used if PCCs or the PCE did not
   advertise their stateful SFP instantiation capability,Section 5.1.
   If this is not the case and stateful operations on SFPs are
   attempted, then a PCErr message with error-type 19 (Invalid
   Operation) and error-value TBD needs to be generated.

   [Editor's note: more information on exact error value is needed]

7.  SFP Instantiation Signaling and Forwarding Considerations

   The PCE-initiated SFP instantiation signaling described in this
   document is exchanged between PCE server and SFC Classifier and does
   not assume any specific mechanism to exchange SFP
   information(e.g.,path identification information,metadata
   [I-D.ietf-sfc-nsh]) between SFFs or between SFF and SF, or between
   the controller and SFF and establish SFP in the data plane throughout
   a SFC domain.  For example, such mechanism can rely upon the use of
   the SFC Encapsulation defined in [I-D.ietf-sfc-nsh] to exchange SFP
   information between SFFs or rely upon the use of BGP Control plane
   defined in [I-D.ietf-bess-nsh-bgp-control-plane] to exchange SFP
   information between the Controller and SFF.

   Likewise, [I-D.ietf-teas-pce-central-control] can use the signaling
   mechanism described in this draft to enforce SFC-inferred traffic
   engineering policies and provide load balancing between service
   function nodes.  The approach that relies upon the Segment Routing
   technique [I-D.ietf-pce-segment-routing] can also take advantage of



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   the signaling mechanism described in this document to support Service
   Path instantiation, which does not require any additional specific
   extension to the Segment Routing machinery.

8.  Security Considerations

   The security considerations described in [RFC5440] and
   [I-D.ietf-pce-pce-initiated-lsp] are applicable to this
   specification.  This document does not raise any additional security
   issue.

9.  IANA Considerations

   IANA is requested to allocate a new code point in the PCEP TLV Type
   Indicators registry, as follows:

      Value   Meaning                      Reference
      ------- ---------------------------- --------------
      TBD     SFC-PCE-CAPABILITY           This document

10.  Acknowledgements

   Many thanks to Ron Parker, Hao Wang, Dave Dolson, Jing Huang, and
   Joel M.  Halpern for the discussion about the content for the
   document.

11.  References

11.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [I-D.ietf-pce-stateful-pce]
              Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
              Extensions for Stateful PCE", draft-ietf-pce-stateful-
              pce-21 (work in progress), June 2017.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.







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   [I-D.ietf-pce-pce-initiated-lsp]
              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-10 (work in
              progress), June 2017.

   [I-D.ietf-teas-pce-central-control]
              Farrel, A., Zhao, Q., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and PCEP in a Network with
              Central Control", draft-ietf-teas-pce-central-control-03
              (work in progress), June 2017.

11.2.  Informative References

   [RFC2753]  Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
              for Policy-based Admission Control", RFC 2753,
              DOI 10.17487/RFC2753, January 2000,
              <http://www.rfc-editor.org/info/rfc2753>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <http://www.rfc-editor.org/info/rfc7665>.

   [RFC5394]  Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
              "Policy-Enabled Path Computation Framework", RFC 5394,
              DOI 10.17487/RFC5394, December 2008,
              <http://www.rfc-editor.org/info/rfc5394>.

   [I-D.ietf-sfc-control-plane]
              Boucadair, M., "Service Function Chaining (SFC) Control
              Plane Components & Requirements", draft-ietf-sfc-control-
              plane-08 (work in progress), October 2016.

   [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-09 (work in progress),
              April 2017.

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-12 (work in progress), February 2017.

   [I-D.ietf-bess-nsh-bgp-control-plane]
              Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
              Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess-
              nsh-bgp-control-plane-00 (work in progress), March 2017.



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Authors' Addresses

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: bill.wu@huawei.com


   Dhruv Dhody
   Huawei
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.ietf@gmail.com


   Mohamed Boucadair
   Orange
   Rennes 35000
   France

   EMail: mohamed.boucadair@orange.com


   Christian Jacquenet
   Orange
   Rennes
   France

   EMail: christian.jacquenet@orange.com


   Jeff Tantsura
   2330 Central Expressway
   Santa Clara, CA  95050
   US

   EMail: jefftant.ietf@gmail.com









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