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SFC                                                          B. Sarikaya
Internet-Draft                                       Denpel Informatique
Intended status: Standards Track                             D. von Hugo
Expires: August 12, 2019                                Deutsche Telekom
                                                            M. Boucadair
                                                                  Orange
                                                        February 8, 2019


      Service Function Chaining: Subscriber and Performance Policy
  Identification Variable-Length Network Service Header (NSH) Context
                                Headers
                   draft-ietf-sfc-serviceid-header-02

Abstract

   This document defines Subscriber and Performance Policy Identifiers
   Network Service Header Variable-Length Context Headers to inform
   Service Functions about subscriber- and service-related information
   for the sake of policy enforcement and appropriate service function
   chaining operations.  The structure of each context header is
   defined, their use and processing instructions by SFC-aware nodes are
   explained.

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 August 12, 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



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   (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.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
   3.  Subscriber Identification NSH Variable-Length Context Header    4
   4.  Performance Policy Identification NSH Variable-Length Context
       Headers . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document discusses how to inform Service Functions (SFs,
   [RFC7665]) about subscriber- and service-related information, when
   required, for the sake of policy enforcement within a single
   administrative domain.  Particularly, subscriber-related information
   may be required to enforce subscriber-specific SFC-based traffic
   policies.  Nevertheless, the information carried in packets may not
   be sufficient to unambiguously identify a subscriber.  This document
   fills this void by specifying a new Network Service Header (NSH)
   [RFC8300] context header to convey and disseminate such information
   within the boundaries of a single administrative domain.

   Also, the enforcement of SFC-based differentiated traffic policies
   may be inferred, for example, by QoS (Quality of Service)
   considerations.  Typically, QoS information may serve as an input to
   the Service Function Path (SFP) for path computation, establishment,
   and selection.  Furthermore, the dynamic structuring of service
   function chains and their subsequent enforcement may be conditioned
   by QoS requirements that will affect SF instance identification,
   location, and sequencing.  Hence, the need to supply a performance
   policy identifier to upstream SFs to appropriately meet the service
   requirements arises.




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   SFs and SF Forwarders (SFFs) involved in a service chain have to
   contribute to the respective service policy (QoS, for example)
   requirements characterized by low transmission delay between each
   other, by exposing a high availability of resources to process
   function tasks, or by redundancy provided by stand-by machines for
   seamless execution continuation in case of failures.  These
   requirements may be satisfied by means of control plane protocols,
   but in some contexts, e.g., in networks where resources are very much
   constrained, carrying QoS-related information directly in packets may
   improve the overall SFC operation instead of relying upon the
   potential complexity or adding overhead introduced by some SFC
   control plane features.  This information is typically included as
   context header in the NSH.

   The context information defined in this document can be applicable in
   the context of mobile networks (typically, in the 3GPP defined (S)Gi
   Interface) [I-D.ietf-sfc-use-case-mobility].  Because of the
   widespread use of private addressing in those networks, if SFs to be
   invoked are located after a NAT function (that can reside in the
   Packet Data Network (PDN) Gateway (PGW) or in a distinct node), the
   identification based on the internal IP address is not possible once
   the NAT has been crossed.  As such, means to allow passing the
   internal information may optimise packet traversal within an SFC-
   enabled mobile network domain.  Furthermore, some SFs that are not
   enabled on the PGW may require a subscriber identifier to properly
   operate.  It is out of scope of this document to include a
   comprehensive list of deployment contexts which may make use of the
   context headers defined in the document.

   This document does not make any assumption about the structure of
   subscriber or performance policy identifiers; each such identifier is
   treated as an opaque value.  The semantics and validation of these
   identifiers are up to the control plane used for SFC.  Expectations
   to SFC control plane protocols are laid down, e.g., in [RFC8459], but
   specifications of SFC control plane functions are also discussed in,
   for example, [I-D.ietf-bess-nsh-bgp-control-plane].  Control plane
   related considerations are out of scope.

   This document assumes the NSH is used exclusively within a single
   administrative domain.

   This document adheres to the architecture defined in [RFC7665].  This
   document assumes the reader is familiar with [RFC8300].








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2.  Conventions and Terminology

   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.

   The reader should be familiar with the terms defined in [RFC7665].

3.  Subscriber Identification NSH Variable-Length Context Header

   Subscriber Identifier is defined as an optional variable-length NSH
   context header.  Its structure is shown in Figure 1.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Metadata Class       |      Type     |U|    Length   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                      Subscriber Identifier                    ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 1: Subscriber Identifier Variable-Length Context Header

   The description of the fields is as follows:

   o  Metadata Class: MUST be set to 0x0 [RFC8300].

   o  Type: TBD1 (See Section 5)

   o  Subscriber Identifier: Carries an opaque subscriber identifier.

   The subscriber identifier is used to convey an identifier assigned by
   the service provider to uniquely identify a subscriber.  This
   subscriber identifier can be used by service functions to enforce
   per-subscriber policies.

   The classifier and SFC-aware SFs MAY be instructed via a control
   interface to inject or strip a subscriber identifier context header.
   Also, the data to be injected in such header SHOULD be configured to
   nodes authorized to inject such headers.  Typically, a node can be
   instructed to insert such data following a type/set scheme (e.g.,
   node X should inject subscriber ID type Y).  Other schemes may be
   envisaged.





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   Failures to inject such headers SHOULD be logged locally while a
   notification alarm MAY be sent to a Control Element.  The details of
   sending notification alarms (i.e., the parameters affecting the
   transmission of the notification alarms depend on the information in
   the context header such as frequency, thresholds, and content in the
   alarm (full header, header ID, timestamp), etc.)  SHOULD be
   configurable by the control plane.

   This document adheres to the recommendations in [RFC8300] for
   handling the context headers at both ingress and egress SFC boundary
   nodes.  That is, to strip such context headers.  Revealing any
   personal and subscriber-related information to third parties is
   avoided by design to prevent privacy breaches in terms of user
   tracking.

   SFC-aware SFs and proxies MAY be instructed to strip a subscriber
   identifier context header from the packet or to pass the data to the
   next SF in the service chain after processing the content of the
   context headers.  If no instruction is provided, the default behavior
   for intermediary SFC-aware nodes is to maintain such context headers
   so that the information can be passed to next SFC-aware hops.

   SFC-aware SFs MAY be instructed via the control plane about the
   validation checks to run on the content of these context headers
   (e.g., accept only some lengths) and the behavior to adopt.  For
   example, SFC-aware SFs may be instructed to ignore the context
   header, to remove the context header from the packet, etc.
   Nevertheless, this specification does not require nor preclude such
   additional validation checks.  These validation checks are
   deployment-specific.  If validation checks fail on a subscriber
   identifier context header, an SFC-aware SF MUST ignore that context
   header.  The event SHOULD be logged locally while a notification
   alarm MAY be sent to a Control Element if the SFC-aware SF is
   instructed to do so.

   Multiple subscriber Identifier context TLVs MAY be present in the NSH
   each carrying a distinct opaque value but all pointing to the same
   subscriber.  When multiple subscriber identifier context TLVs are
   present and an SF is instructed to strip the subscriber identifier
   context header, that SF has to remove all subscriber identifier
   context TLVs.

4.  Performance Policy Identification NSH Variable-Length Context
    Headers

   Dedicated service-specific performance identifier is defined to
   differentiate between services requiring specific treatment to
   exhibit a performance characterized by, e.g., ultra-low latency (ULL)



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   or ultra-high reliability (UHR).  Other policies can be considered
   when instantiating a service function chain within an SFC-enabled
   domain.  They are conveyed in the Performance Policy Identifier
   context header.

   The performance policy identifier is inserted in an NSH packet so
   that upstream SFC-aware nodes can make use of the performance
   information for proper distributed SFC path selection, SF instance
   selection, or policy selection at SFs.

   Thus, the performance policy identifier allows for the distributed
   enforcement of a per-service policy such as a service function path
   to only include specific SFs instances.  Details of this process are
   implementation-specific.  For illustration purposes, an SFF may
   retrieve the details of usable SFs based upon the corresponding
   performance policy identifier.  Typical criteria for instantiating
   specific SFs include location, performance, or proximity
   considerations.  For the particular case of UHR services, the stand-
   by operation of back-up capacity or the deployment of multiple SF
   instances may be requested.

   Performance Policy Identifier is defined as optional variable length
   context header.  Its structure is shown in Figure 2.

   Similar control plane considerations as those discussed in Section 3
   are to be followed.

   Multiple performance policy identifier context headers MAY be present
   in the NSH; each carrying a distinct opaque value but all are
   pointing to policies that need to be enforced for a flow.  It is up
   to the control plane to ensure that these policies are not
   conflicting.  When such conflict is detected by an SFC-aware node,
   the default behavior of the node is to discard the packet and send a
   notification alarm to a Control Element.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Metadata Class       |      Type     |U|    Length   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                     Performance Policy Identifier                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 2: Performance Policy Identifier Variable-Length Context
                                  Header

   The description of the fields is as follows:



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   o  Metadata Class: MUST be set to 0x0 [RFC8300].

   o  Type: TBD2 (See Section 5)

   o  Performance Policy Identifier: Represents an opaque value pointing
      to specific performance policy to be enforced.  The structure and
      semantic of this field is deployment-specific.

5.  IANA Considerations

   This document requests IANA to assign the following types from the
   "NSH IETF- Assigned Optional Variable-Length Metadata Types" (0x0000
   IETF Base NSH MD Class) registry available at:
   https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable-
   length-metadata-types.

        +-------+-------------------------------+----------------+
        | Value | Description                   | Reference      |
        +-------+-------------------------------+----------------+
        | TBD1  | Subscriber Identifier         | [ThisDocument] |
        | TBD2  | Performance Policy Identifier | [ThisDocument] |
        +-------+-------------------------------+----------------+

6.  Security Considerations

   Data plane SFC-related security considerations, including privacy,
   are discussed in [RFC7665] and [RFC8300].

   Nodes that are involved in an SFC-enabled domain are assumed to be
   trusted ([RFC8300]).  Means to check that only authorized nodes are
   solicited when a packet is crossing an SFC-enabled domain are out of
   scope of this document.

   A misbehaving node within from the SFC-enabled domain may alter the
   content of Subscriber and Performance Policy TLVs which may lead to
   service disruption.  Such attach is not unique to the TLVs documents
   defined in the document; measures discussed in [RFC8300] are to be
   followed.  Also, integrity checks offered by the transport
   encapsulation can be used to detect anomalies.

   An SF maintaining logs for operational reasons MUST NOT log the
   content of Subscriber and Performance Policy context headers received
   in NSH packets if the SF does not use the content of that header for
   its operation.







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7.  Acknowledgements

   Comments from Joel Halpern on a previous version and by Carlos
   Bernardos are appreciated.

   Contributions and review by Christian Jacquenet, Danny Lachos,
   Debashish Purkayastha, Christian Esteve Rothenberg, and Kyle Larose
   are thankfully acknowledged.

8.  Change Log

   o  submitted version -00 as a working group draft after adoption

   o  submitted version -01 for editorial improvements

   o  submitted version -02 with these changes: fixed the abbreviated
      title, corrected typos, editorial improvements, rename policy
      identifier as performance policy identifier

9.  References

9.1.  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>.

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

   [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>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

9.2.  Informative References

   [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-05 (work in progress), January 2019.



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   [I-D.ietf-sfc-use-case-mobility]
              Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and
              J. Uttaro, "Service Function Chaining Use Cases in Mobile
              Networks", draft-ietf-sfc-use-case-mobility-09 (work in
              progress), January 2019.

   [RFC8459]  Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
              "Hierarchical Service Function Chaining (hSFC)", RFC 8459,
              DOI 10.17487/RFC8459, September 2018,
              <https://www.rfc-editor.org/info/rfc8459>.

Authors' Addresses

   Behcet Sarikaya
   Denpel Informatique

   Email: sarikaya@ieee.org


   Dirk von Hugo
   Deutsche Telekom
   Deutsche-Telekom-Allee 7
   D-64295 Darmstadt
   Germany

   Email: Dirk.von-Hugo@telekom.de


   Mohamed Boucadair
   Orange
   Rennes 3500
   France

   Email: mohamed.boucadair@orange.com

















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